Laser interferometer

Abstract

This invention provides a laser interferometer that can suppress the reduction in demodulation accuracy even when subjected to external interference such as temperature changes. The laser interferometer includes: a laser source that emits laser light; an optical modulator that includes a vibrating element driven by a drive signal and superimposes the modulated signal onto the laser light; a light-receiving element that receives a laser light containing a sampled signal superimposed by reflection from an object and a laser light containing the modulated signal, and outputs a received light signal; a calculation unit that performs calculations on the received light signal based on a reference signal; and a signal generation unit that outputs a drive signal and a reference signal. The calculation unit includes: a preprocessing unit that outputs a preprocessed signal containing a frequency modulation component based on the reference signal; a demodulation processing unit that demodulates the sampled signal from the preprocessed signal based on the reference signal; and a correction processing unit that outputs a correction signal based on an output signal corresponding to the drive of the vibrating element. The signal generation unit corrects the drive signal and the reference signal based on the correction signal.

Description

Technical Field

[0001] This invention relates to laser interferometers. Background Technology

[0002] Patent Document 1 discloses a laser vibrator (laser interferometer) that irradiates an object with laser light and measures the vibration velocity based on the scattered laser light subjected to Doppler frequency shift. In this laser vibrator, the Doppler signal contained in the scattered laser light is extracted using optical heterodyne interferometry.

[0003] Furthermore, in the laser vibrator described in Patent Document 1, piezoelectric elements or quartz oscillators are used, and the frequency is shifted by irradiating these vibrating elements with laser light. The Doppler signal is demodulated from the scattered laser light by using a laser light containing a modulated signal with such a shifted frequency as a reference light. Moreover, the vibration velocity of an object can be measured based on the obtained Doppler signal.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2007-285898

[0005] For example, in the case of a quartz oscillator, its mechanical resonant frequency varies with the ambient temperature. Therefore, when using a quartz oscillator to shift the frequency of a laser to generate a modulation signal, the modulation signal changes with temperature. Consequently, the signal-to-noise ratio (S / N ratio) of the modulation signal decreases, leading to a reduction in the demodulation accuracy of the Doppler signal. Therefore, realizing a laser interferometer that can suppress the reduction in demodulation accuracy even when subjected to external interference such as temperature changes has become a challenge. Summary of the Invention

[0006] The laser interferometer described in the application example of the present invention is characterized by comprising: a laser source that emits laser light; an optical modulator that includes a vibrating element driven by a drive signal and uses the vibrating element to overlap the modulation signal with the laser light; a light-receiving element that receives the laser light including a sampled signal that is superimposed by reflection from an object and the laser light including the modulation signal, and outputs a light-receiving signal; an arithmetic unit that performs arithmetic on the light-receiving signal according to a reference signal; and a signal generation unit that outputs the drive signal and the reference signal. The arithmetic unit includes: a preprocessing unit that performs preprocessing to extract a frequency modulation component from the light-receiving signal according to the reference signal and outputs a preprocessed signal including the frequency modulation component; a demodulation processing unit that demodulates the sampled signal from the preprocessed signal according to the reference signal; and a correction processing unit that outputs a correction signal according to an output signal output corresponding to the drive of the vibrating element. The signal generation unit corrects the drive signal and the reference signal according to the correction signal. Attached Figure Description

[0007] Figure 1This is a functional block diagram illustrating the laser interferometer according to the first embodiment.

[0008] Figure 2 It means Figure 1 A schematic diagram of the sensor head.

[0009] Figure 3 It means Figure 2 A three-dimensional view of the first configuration example of an optical modulator.

[0010] Figure 4 This is a top view showing a portion of a second configuration example of an optical modulator.

[0011] Figure 5 This is a top view showing a third configuration example of an optical modulator.

[0012] Figure 6 This indicates that in the incident light K i A conceptual diagram illustrating the generation of multiple diffracted beams when incident from a direction perpendicular to the surface of the vibrating element.

[0013] Figure 7 This explains the composition of the incident light K. i A conceptual diagram of an optical modulator whose direction of travel forms an angle of 180° with the direction of travel of the reference light L2.

[0014] Figure 8 This explains the composition of the incident light K. i A conceptual diagram of an optical modulator whose direction of travel forms an angle of 180° with the direction of travel of the reference light L2.

[0015] Figure 9 This explains the composition of the incident light K. i A conceptual diagram of an optical modulator whose direction of travel forms an angle of 180° with the direction of travel of the reference light L2.

[0016] Figure 10 It is a detailed representation Figure 1 The diagram of the arithmetic unit in the function block diagram.

[0017] Figure 11 It means Figure 10 The flowchart shows an example of a method for setting the phase quantity using the phase quantity setting unit.

[0018] Figure 12 It means according to Figure 11 The illustrated process includes examples of waveforms of the preprocessed signal S(t) before laser interferometer calibration, the phase information after demodulation by the demodulation processing unit (phase information before expansion), and the phase information after phase expansion processing by the signal output unit (phase information after expansion).

[0019] Figure 13 It means according to Figure 11 The illustrated process includes examples of waveforms of the preprocessed signal S(t) after correction by the laser interferometer, the phase information after demodulation by the demodulation processing unit (phase information before expansion), and the phase information after phase expansion processing by the signal output unit (phase information after expansion).

[0020] Figure 14 It is a detailed representation Figure 1 The diagram shows the correction processing unit in the functional block diagram.

[0021] Figure 15 This is a diagram illustrating an example of a circuit that acquires the output signal Sm from an optical modulator.

[0022] Figure 16 This is a functional block diagram illustrating the laser interferometer involved in the second embodiment.

[0023] Figure 17 It is a detailed representation Figure 16 The diagram shows the arithmetic unit and signal generation unit in the functional block diagram.

[0024] Figure 18 This is a schematic diagram showing the configuration of the optical system involved in the first variation.

[0025] Figure 19 This is a schematic diagram showing the configuration of the optical system involved in the second variation.

[0026] Figure 20 This is a schematic diagram showing the optical system involved in the third variation.

[0027] Figure 21 This is a schematic diagram showing the optical system involved in the fourth variation.

[0028] Explanation of reference numerals in the attached figures

[0029] 1…Laser interferometer, 1a…Laser interferometer, 2…Laser source, 3…Collimating lens, 4…Optical splitter, 6…1 / 2 wavelength plate, 7…1 / 4 wavelength plate, 8…1 / 4 wavelength plate, 9…Analyzer, 10…Light receiving element, 12…Optical modulator, 14…Object, 18…Optical path, 20…Optical path, 22…Optical path, 24…Optical path, 30…Vibrating element, 30A…Vibrating element, 30B…Vibrating element, 31…Substrate, 32…Groove, 33…Pad, 34…Diffraction grating, 35…Pad, 36…Vibration direction, 37…Mirror, 45…Circuit element, 50…Optical system, 50A…Optical system, 50B…Optical system, 50C…Optical system, 50D…Optical system, 51…Sensor head, 5 2…Arithmetic unit, 53…Preprocessing unit, 55…Demodulation processing unit, 57…Quadrature signal generation unit, 59…Main body unit, 61…Signal generation unit, 61a…Signal generation unit, 62…Correction processing unit, 62a…Correction processing unit, 64…Current shunt monitor, 120…Optical modulation oscillator, 301…First electrode, 302…Second electrode, 303…Diffraction grating mounting unit, 305…Piezoelectric substrate, 306…Comb-shaped electrode, 307…Ground electrode, 311…Surface, 312…Back side, 531…Current-to-voltage converter, 532…ADC, 533…ADC, 534…First bandpass filter, 535…Second bandpass filter, 536…First delay adjuster, 538…Multiplier, 539…Third… Bandpass filter, 540… First AGC section, 541… Second AGC section, 542… Adder, 543… ADC, 551… Multiplier, 552… Multiplier, 553… Inverting amplifier, 555… First low-pass filter, 556… Second low-pass filter, 557… Divider, 558… Arctangent operator, 559… Signal output section, 571… Fourth bandpass filter, 572… Hilbert transform filter, 573… Second delay adjuster, 574… Reference signal phase operator, 577… Absolute value operator, 578… Third low-pass filter, 579… Phase setting section, 580… Adder, 581… Cosine generator, 582… Sine generator, 612… Voltage controlled oscillator, 6 14…Amplifier, 615…DAC, 616…Numerically controlled oscillator, 621…Absolute value operator, 622…Multiplier, 623…Multiplier, 624…Fourth low-pass filter, 625…Fifth low-pass filter, 626…Amplitude gain setting unit, 627…Frequency setting unit, 631…First offset removal unit, 632…Second offset removal unit, 641…Shunt resistor, 642…Operational amplifier, 643…ADC, 651…Accumulator adder, 652…Adder, 653…First cycle signal generator, 654…Second cycle signal generator, 661…Multiplier, 662…Multiplier, 663…Sixth low-pass filter, 664…Seventh low-pass filter, 665…Amplitude and phase operation unit, K.-2s …diffraction light, K -1s …diffraction light, K 0s …diffraction light, K 1s …diffraction light, K 2s …Diffraction light, K1…Incident light, L1…Outgoing light, L1a…First segmented light, L1b…Second segmented light, L2…Reference light, L3…Object light, N…Normal, P…Spacing, S1…First signal, S2…Second signal, S102…Process, S104…Process, S106…Process, S108…Process, S110…Process, S112…Process, S114…Process, S116…Process, S118…Process, S120…Process, cos(θ) m (t))…cosine wave signal, sin(θ) m (t))…sine wave signal, S(t)…preprocessed signal, Sa…amplitude signal, Sam…amplification control signal, Sd…drive signal, Sf1…frequency control signal, Sf2…frequency control signal, Sm…output signal, Ss…reference signal, Ss'…reference signal, jp1…bifraction, jp2…bifraction, ps1…first signal path, ps2…second signal path, i…signal i, r…signal r, I…signal I, Q…signal Q, x…signal x, y…signal y, β…incident angle, θ B …Brightness angle, θ S …tilt angle. Detailed Implementation

[0030] The laser interferometer of the present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0031] 1. First Implementation Method

[0032] First, the laser interferometer involved in the first embodiment will be described.

[0033] Figure 1 This is a functional block diagram illustrating the laser interferometer according to the first embodiment. Figure 2 It means Figure 1 A schematic diagram of the sensor head 51.

[0034] Figure 1 The laser interferometer 1 shown includes a sensor head 51 and a main body 59. The sensor head 51 is easily miniaturized and lightweight, and is portable and easy to set up; therefore, it can be configured, for example, as the object being measured by the laser interferometer 1. Figure 2 Near the object 14 shown. The main body 59 can be configured separately from the sensor head 51, for example, it can also be stored in a bracket or the like.

[0035] 1.1. Sensor Head

[0036] Figure 1 The sensor head 51 shown includes an optical system 50, a current-to-voltage converter 531, a signal generation unit 61, and a correction processing unit 62. Figure 1 The main body 59 shown includes a preprocessing unit 53, an orthogonal signal generation unit 57, a demodulation processing unit 55, and a signal output unit 559.

[0037] 1.1.1. Optical System

[0038] like Figure 2 As shown, the 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, an analyzer 9, a light-receiving element 10, and a frequency shifter-type optical modulator 12.

[0039] Laser source 2 emits outgoing light L1 (laser). Light receiving element 10 converts the received light into an electrical signal. Optical modulator 12 has a vibrating element 30 that changes the frequency of outgoing light L1 to generate reference light L2 (laser containing a modulation signal) containing a modulation signal. Outgoing light L1 incident on object 14 is reflected as object light L3 (laser containing a sampling signal), which contains a sampling signal originating from object 14 as a Doppler signal.

[0040] The optical path connecting the optical splitter 4 and the laser source 2 is designated as optical path 18. The optical path connecting the optical splitter 4 and the optical modulator 12 is designated as optical path 20. The optical path connecting the optical splitter 4 and the object 14 is designated as optical path 22. The optical path connecting the optical splitter 4 and the light-receiving element 10 is designated as optical path 24. Furthermore, the term "optical path" in this specification refers to the path of light travel between optical components.

[0041] On optical path 18, starting from the side of optical splitter 4, a half-wave plate 6 and a collimating lens 3 are arranged sequentially. On optical path 20, a quarter-wave plate 8 is arranged. On optical path 22, a quarter-wave plate 7 is arranged. On optical path 24, an analyzer 9 is arranged.

[0042] The emitted light L1 from the laser source 2 is split into two by the optical splitter 4 via optical path 18. The first split light L1a, one of the split emitted light L1, is incident on the optical modulator 12 via optical path 20. The second split light L1b, the other of the split emitted light L1, is incident on the object 14 via optical path 22. The reference light L2, generated by frequency modulation by the optical modulator 12, is incident on the light-receiving element 10 via optical paths 20 and 24. The object light L3, generated by reflection from the object 14, is incident on the light-receiving element 10 via optical paths 22 and 24.

[0043] The following is a further explanation of each part of the optical system 50.

[0044] 1.1.1.1. Laser source

[0045] Laser source 2 is a laser source that emits coherent outgoing light L1. Laser source 2 preferably uses a light source with a linewidth of MHz or less. Specifically, examples include gas lasers such as He-Ne lasers, semiconductor laser elements such as DFB-LD (Distributed Feedback-Laser Diode), FBG-LD (Laser Diode with Fiber Bragg Grating), VCSEL (Vertical Cavity Surface Emitting Laser), and FP-LD (Fabry-Perot Laser Diode).

[0046] The laser source 2 is preferably a semiconductor laser element. This allows for the miniaturization of the laser source 2. Consequently, miniaturization of the laser interferometer 1 can be achieved. In particular, since the sensor head 51 housing the optical system 50 in the laser interferometer 1 can be miniaturized and lightened, it is useful in improving the operability of the laser interferometer 1, such as the degree of freedom in the placement of the sensor head 51.

[0047] 1.1.1.2. Collimating Lens

[0048] The collimating lens 3 is an optical element disposed between the laser source 2 and the light splitter 4. An aspherical lens can be used as an example. The collimating lens 3 parallelizes the outgoing light L1 emitted from the laser source 2. Furthermore, if the outgoing light L1 emitted from the laser source 2 is sufficiently parallelized, the collimating lens 3 can be omitted when the laser source 2 uses a gas laser such as a He-Ne laser.

[0049] On the other hand, when the laser source 2 is a semiconductor laser element, the laser interferometer 1 preferably includes a collimating lens 3 disposed between the laser source 2 and the optical splitter 4. This allows the outgoing light L1 emitted from the semiconductor laser element to be parallelized. As a result, the outgoing light L1 becomes collimated, thus suppressing the enlargement of various optical components receiving the outgoing light L1 and enabling miniaturization of the laser interferometer 1.

[0050] The collimated outgoing light L1 passes through the 1 / 2 wavelength 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 then incident on the light splitter 4.

[0051] 1.1.1.3. Optical splitter

[0052] The optical splitter 4 is a polarization beam splitter disposed between the laser source 2 and the optical modulator 12, and between the laser source 2 and the object 14. The optical splitter 4 has the function of allowing P-polarized light to pass through while reflecting S-polarized light. Through this function, the optical splitter 4 splits the outgoing light L1 into a first split beam L1a, which is the reflected light in the optical splitter 4, and a second split beam L1b, which is the transmitted light in the optical splitter 4.

[0053] The first segmented light L1a, which is S-polarized light reflected by the optical splitter 4, is converted into circularly polarized light by the quarter-wave plate 8 and incident on the optical modulator 12. The first segmented light L1a incident on the optical modulator 12 is subjected to f m A frequency shift of [Hz] is achieved, and the light is reflected as reference light L2. Therefore, reference light L2 contains a frequency f. m The modulation signal is [Hz]. When the reference light L2 passes through the quarter-wave plate 8 again, it is converted into P-polarized light. The P-polarized light of the reference light L2 passes through the optical splitter 4 and the analyzer 9 and is incident on the light receiving element 10.

[0054] The second segmented light L1b, which is P-polarized light that has passed through the light splitter 4, is converted into circularly polarized light by the quarter-wave plate 7 and incident on the moving object 14. The second segmented light L1b incident on the object 14 is subjected to f d The Doppler frequency shift of [Hz] is reflected as object light L3. Therefore, object light L3 contains frequency f. d The sampling signal is [Hz]. When the object light L3 passes through the 1 / 4 wavelength plate 7 again, it is converted into S-polarized light. The S-polarized light of the object light L3 is reflected by the light splitter 4 and passes through the analyzer 9 to be incident on the light receiving element 10.

[0055] As mentioned above, since the emitted light L1 is coherent, the reference light L2 and the object light L3 are incident on the light receiving element 10 as interference light.

[0056] Alternatively, a non-polarizing beam splitter can be used instead of a polarizing beam splitter. In this case, the half-wave plate 6, quarter-wave plate 7, and quarter-wave plate 8 are not needed, thus miniaturizing the laser interferometer 1 can be achieved by reducing the number of components. Alternatively, an optical splitter other than a beam splitter can also be used.

[0057] 1.1.1.4. Analyzer

[0058] The S-polarized and P-polarized beams, being orthogonal to each other, are independent and therefore simply coincident without interference causing beat frequencies. Thus, a light wave superimposed with S-polarized and P-polarized light is passed through an analyzer 9 tilted at 45° relative to both S-polarized and P-polarized beams. By using the analyzer 9, light with common components can pass through each other, thus producing interference. As a result, in the analyzer 9, the reference beam L2 interferes with the object beam L3, generating a beam with |f|. m -f d Interference light with a frequency of [Hz].

[0059] 1.1.1.5. Light-receiving element

[0060] When the interference light is incident on the light-receiving element 10, the light-receiving element 10 outputs a photocurrent (light-receiving signal) corresponding to the intensity of the interference light. By demodulating the sampled signal from this light-receiving signal using the method described later, the motion, i.e., displacement and velocity, of the object 14 can be finally determined. Examples of light-receiving elements 10 include photodiodes. Furthermore, the light received by the light-receiving element 10 is not limited to interference light, as long as it contains both a sampled signal and a modulation signal. Additionally, "demodulating the sampled signal from the light-receiving signal" in this specification includes demodulating the sampled signal from various signals converted from the photocurrent (light-receiving signal).

[0061] 1.1.1.6. Optical Modulator

[0062] Figure 3 It means Figure 2 A perspective view of a first configuration example of the optical modulator 12.

[0063] 1.1.1.6.1. Summary of the First Configuration Example of an Optical Modulator

[0064] The frequency shifter type optical modulator 12 has an optical modulation oscillator 120. Figure 3 The optical modulation oscillator 120 shown has a plate-shaped vibrating element 30 and a substrate 31 supporting the vibrating element 30.

[0065] The vibrating element 30 is made of a material that repeatedly vibrates in a manner that distorts in the direction along the surface when an electrical potential is applied. In this configuration example, the vibrating element 30 is an AT-cut quartz oscillator that undergoes thickness shear vibration along the vibration direction 36 in the high-frequency region of the MHz band. A diffraction grating 34 is formed on the surface of the vibrating element 30. The diffraction grating 34 has grooves 32 that hold components intersecting the vibration direction 36, that is, a plurality of straight grooves 32 extending in a direction intersecting the vibration direction 36.

[0066] The substrate 31 has a surface 311 and a back surface 312 that are in a face-to-back relationship. A vibrating element 30 is disposed on the surface 311. In addition, pads 33 for applying a potential to the vibrating element 30 are provided on the surface 311. On the other hand, pads 35 for applying a potential to the vibrating element 30 are also provided on the back surface 312.

[0067] The size of the substrate 31 is, for example, approximately 0.5 mm or more and 10.0 mm or less on the long side. Additionally, the thickness of the substrate 31 is, for example, approximately 0.10 mm or more and 2.0 mm or less. As an example, the substrate 31 is a square with one side measuring 1.6 mm, and its thickness is 0.35 mm.

[0068] The size of the vibrating element 30 is, for example, about 0.2 mm or more and about 3.0 mm or less on the long side. In addition, the thickness of the vibrating element 30 is, for example, about 0.003 mm or more and about 0.5 mm or less.

[0069] As an example, the vibrating element 30 is a square with one side of 1.0 mm and a thickness of 0.07 mm. In this case, the vibrating element 30 oscillates at a fundamental oscillation frequency of 24 MHz. Furthermore, by changing the thickness of the vibrating element 30 or taking into account harmonics (overtones), the oscillation frequency can be adjusted in the range of 1 MHz to 1 GHz.

[0070] In addition, Figure 3 In this process, the diffraction grating 34 is formed on the entire surface of the vibrating element 30, but it may also be formed on only a portion of it.

[0071] The magnitude of the optical modulation of the optical modulator 12 is given by the inner product of the difference wavenumber vector of the wavenumber vector of the outgoing light L1 incident on the optical modulator 12 and the wavenumber vector of the reference light L2 emitted from the optical modulator 12, and the vector of the vibration direction 36 of the vibrating element 30. In this configuration example, the vibrating element 30 performs thickness shear vibration, but since this vibration is in-plane vibration, optical modulation cannot be performed even if light is incident perpendicularly to the surface of the vibrating element 30. Therefore, in this configuration example, by providing a diffraction grating 34 on the vibrating element 30, optical modulation can be performed according to the principle described later.

[0072] Figure 3 The diffraction grating 34 shown is a blazed diffraction grating. A blazed diffraction grating is a grating with a stepped cross-sectional shape. The straight grooves 32 of the diffraction grating 34 are arranged such that their extension direction is orthogonal to the vibration direction 36.

[0073] When from Figure 1 and Figure 2 The signal generation unit 61 shown is directed towards Figure 3When the vibration element 30 shown is supplied with a drive signal Sd (an AC voltage is applied), the vibration element 30 oscillates. The power (drive power) required for the oscillation of the vibration element 30 is not particularly limited, ranging from about 0.1 μW to about 100 mW. Therefore, miniaturization and weight reduction of the sensor head 51 can be easily achieved.

[0074] Furthermore, existing optical modulators sometimes require structures to maintain their temperature, making it difficult to reduce their size. In contrast, in this configuration example, since no temperature-maintaining structure is needed, the size of the vibrating element 30 is very small. Therefore, from this perspective, miniaturization and power saving of the laser interferometer 1 are also easier.

[0075] 1.1.1.6.2. Methods for forming diffraction gratings

[0076] The method for forming the diffraction grating 34 is not particularly limited. As an example, one method is to fabricate a mold using a mechanical scribing method (scrubbing machine) and then form a groove 32 on the electrode of the vibrating element 30 of the AT-cut quartz oscillator using nanoimprint lithography. The reason for forming the groove on the electrode is that, in the case of the AT-cut quartz oscillator, high-quality thickness shear vibration can theoretically be generated on the electrode. Furthermore, the formation of the groove 32 is not limited to the electrode and can also be on the surface of the material in the non-electrode portion. Alternatively, exposure-based etching methods, electron beam lithography, focused ion beam (FIB) processing, etc., can be used instead of nanoimprint lithography.

[0077] Alternatively, a diffraction grating can be formed on the chip of an AT-cut quartz oscillator using a photoresist material, and a mirror film composed of a metal film or a multilayer dielectric film can be placed on the diffraction grating. By placing a metal film or a mirror film, the reflectivity of the diffraction grating 34 can be improved.

[0078] Furthermore, a resist film can be formed on the chip or wafer of an AT-cut quartz oscillator. After etching, the resist film is removed, and then a metal film or mirror film is formed on the processed surface. In this case, since the resist material is removed, it is not affected by the moisture absorption of the resist material, thus improving the chemical stability of the diffraction grating 34. Additionally, by setting a highly conductive metal film such as Au or Al, it can also be used as an electrode to drive the oscillation element 30.

[0079] In addition, the diffraction grating 34 can also be formed using techniques such as anodic aluminum oxide (porous aluminum oxide).

[0080] 1.1.1.6.3. Other configuration examples of optical modulators

[0081] The vibrating element 30 is not limited to a quartz oscillator; for example, it can also be a Si oscillator, a surface acoustic wave (SAW) device, a ceramic oscillator, etc.

[0082] Figure 4 This is a top view showing a portion of a second configuration example of the optical modulator 12. Figure 5 This is a top view showing a third configuration example of the optical modulator 12.

[0083] Figure 4 The vibrating element 30A shown is a Si oscillator manufactured from a Si substrate using MEMS technology. MEMS (Micro-Electro-Mechanical Systems) is a micro-electromechanical system.

[0084] The vibrating element 30A includes a first electrode 301 and a second electrode 302 adjacent to each other on the same plane with a gap between them, a diffraction grating mounting portion 303 disposed on the first electrode 301, and a diffraction grating 34 disposed on the diffraction grating mounting portion 303. The first electrode 301 and the second electrode 302 are driven, for example, by electrostatic attraction, to... Figure 4 The left and right directions, that is, along Figure 4 The axis connecting the first electrode 301 and the second electrode 302 vibrates by repeatedly approaching and separating from each other. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the Si oscillator is, for example, around 1 kHz to several hundred MHz.

[0085] Figure 5 The vibrating element 30B shown is a SAW device that utilizes surface waves. SAW (Surface Acoustic Wave) is a type of surface acoustic wave.

[0086] The vibrating element 30B includes a piezoelectric substrate 305, a comb-shaped electrode 306 disposed on the piezoelectric substrate 305, a ground electrode 307, a diffraction grating mounting portion 303, and a diffraction grating 34. When an alternating voltage is applied to the comb-shaped electrode 306, a surface acoustic wave (SAW) is excited through the inverse piezoelectric effect. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the SAW device is, for example, around several hundred MHz to several GHz.

[0087] For devices like the above, optical modulation can also be performed according to the principle described later, in the same way as with AT-cut quartz oscillators, by setting diffraction grating 34.

[0088] Furthermore, when the vibrating element 30 is a quartz oscillator, the extremely high Q value of quartz can be used to generate a high-precision modulation signal. The Q value is an indicator of the sharpness of the resonant peak. In addition, quartz oscillators have the advantage of being less susceptible to disturbances. Therefore, by using the modulation signal modulated by the optical modulator 12 equipped with a quartz oscillator, the sampling signal originating from the object 14 can be acquired with high precision.

[0089] 1.1.1.6.4. Optical Modulation Based on Vibrating Elements

[0090] Next, the principle of using the vibrating element 30 to modulate light will be explained.

[0091] Figure 6 This indicates that in the incident light K i A conceptual diagram illustrating the generation of multiple diffracted beams when incident from a direction perpendicular to the surface of the vibrating element 30.

[0092] When incident light Ki is incident on a diffraction grating 34 that undergoes thickness shear vibration along the vibration direction 36, as Figure 6 As shown, multiple diffracted beams K are generated through the diffraction phenomenon. ns n is the diffracted light K ns The number of times, n = 0, ±1, ±2, ... Furthermore, in Figure 6 In the diffraction grating 34 shown, the one illustrated is not... Figure 3 Instead of showing a blazed diffraction grating, this illustration serves as an example of other diffraction gratings, depicting a diffraction grating formed by repeated concave and convex shapes. Furthermore, in Figure 6 In the text, the diffraction light K is omitted. Os The illustration.

[0093] exist Figure 6 In this case, the incident light Ki is incident from a direction perpendicular to the surface of the vibrating element 30, but its incident angle is not particularly limited; it can also be set to be incident at an angle relative to the surface of the vibrating element 30. In the case of oblique incident light, the diffracted light K... ns Its direction of travel also changes accordingly.

[0094] Furthermore, depending on the design of the diffraction grating 34, higher-order light with |n|≥2 may not sometimes appear. Therefore, to obtain a stable modulation signal, it is best to set |n|=1. That is, in Figure 2 In the laser interferometer 1, the preferred frequency shifter type optical modulator 12 is configured to use ±1st order diffracted light as reference light L2. This configuration allows for the stabilization of measurements in the laser interferometer 1.

[0095] On the other hand, in the case where higher-order light with |n|≥2 appears from the diffraction grating 34, the optical modulator 12 can be configured to use any diffracted light of ±2nd order or higher as the reference light L2 instead of ±1st order diffracted light. Thus, since higher-order diffracted light can be utilized, the laser interferometer 1 can be made more frequent and smaller.

[0096] In this embodiment, as an example, the optical modulator 12 is configured such that the angle between the entrance direction of the incident light Ki incident on the optical modulator 12 and the travel direction of the reference light L2 emitted from the optical modulator 12 is 180°. Hereinafter, it will be shown... Figures 7 to 9 Three examples will be used to illustrate this.

[0097] Figures 7 to 9 These are descriptions of the composition of incident light K. i A conceptual diagram of an optical modulator 12 whose direction of travel forms an angle of 180° with the direction of travel of the reference light L2.

[0098] Figure 7 The optical modulator 12 shown includes a mirror 37 in addition to the vibrating element 30. The mirror 37 is configured to diffract the light K 1s The light is reflected back to the diffraction grating 34. At this point, the diffracted light K... 1s The angle between the incident angle and the reflection angle in mirror 37 is 180°. As a result, the diffracted light K exiting from mirror 37 and returning to diffraction grating 34... 1s The light is diffracted again by the diffraction grating 34, and then directed toward the incident light K that is incident on the light modulator 12. i It travels in the opposite direction to the direction of travel. Therefore, by adding mirror 37, the aforementioned incident light K can be satisfied. i The condition is that the angle between the direction of entry of the light and the direction of travel of the reference light L2 is 180°.

[0099] Furthermore, the reference light L2 generated by the optical modulator 12 is subjected to two frequency modulations via mirror 37. Therefore, by using mirror 37, higher frequency modulation can be achieved compared to using a single vibrating element 30.

[0100] exist Figure 8 In, relative to Figure 6 The configuration causes the vibrating element 30 to tilt. The tilt angle θ at this point... S The incident light K is set to satisfy the aforementioned condition. i The condition is that the angle between the direction of entry of the light and the direction of travel of the reference light L2 is 180°.

[0101] Figure 9 The diffraction grating 34 shown has a blaze angle θ BA blazed diffraction grating. Furthermore, when incident light K travels at an incident angle β relative to the normal N of the surface of the vibrating element 30... i When incident on diffraction grating 34, reference light L2 is relative to the normal N with a blaze angle θ. B The same angle returns. Therefore, by making the incident angle β the same as the blaze angle θ B Equal, which satisfies the aforementioned incident light K i The condition is that the angle between the direction of entry of the light beam and the direction of travel of the reference light L2 is 180°. In this case, since no light is used... Figure 7 Mirror 37 as shown, in addition, is not required as Figure 8 As shown, tilting the vibrating element 30 itself satisfies the aforementioned condition, thus enabling further miniaturization and high-frequency operation of the laser interferometer 1. Especially in the case of a blazed diffraction grating, the configuration that satisfies the aforementioned condition is called the "Litterrow configuration," which also has the advantage of significantly improving the diffraction efficiency of the diffracted light.

[0102] also, Figure 9 The spacing P represents the spacing of the blazed diffraction grating; for example, the spacing P is 1 μm. Additionally, the blaze angle θ... B For example, 25°. In this case, to satisfy the condition, it is only necessary to adjust the incident light K... i The incident angle β relative to the normal N can also be set to 25°.

[0103] Furthermore, the diffraction grating 34 can be set as needed. For example, if the vibrating element 30 is an out-of-plane vibrating element, the light modulation efficiency of the outgoing light L1 incident on the vibrating element 30 can be improved even without using the diffraction grating 34. In such cases, the diffraction grating 34 can also be omitted.

[0104] In addition, the vibrating element 30 is not limited to a quartz oscillator; it can be a silicon oscillator or a ceramic oscillator.

[0105] 1.1.2. Current-to-voltage converter

[0106] The current-to-voltage converter 531, also known as a transimpedance amplifier (TIA), converts the photocurrent (photodetector signal) output from the photodetector 10 into a voltage signal and outputs it as a photodetector signal.

[0107] A current-to-voltage converter 531 and an arithmetic unit 52 are disposed between them. Figure 1 The ADC532 is shown. The ADC532 is an analog-to-digital converter that converts analog signals into digital signals at a specified number of sampling bits. The ADC532 is located on the sensor head 51.

[0108] Furthermore, the optical system 50 may also include multiple light-receiving elements 10. In this case, by providing a differential amplifier circuit between the multiple light-receiving elements 10 and the current-to-voltage converter 531, differential amplification processing can be performed on the photocurrent, thereby improving the signal-to-noise ratio (S / N ratio) of the photodetector signal. Furthermore, differential amplification processing can also be performed on voltage signals.

[0109] 1.1.3. Signal generation department

[0110] The signal generation unit 61 outputs a drive signal Sd to the optical modulator 12. Additionally, the signal generation unit 61 outputs a reference signal Ss to the calculation unit 52.

[0111] like Figure 1 As shown, the signal generation unit 61 includes a voltage-controlled oscillator 612 and an amplifier 614.

[0112] The voltage-controlled oscillator 612 is a VCO (Voltage Controlled Oscillator) that controls the frequency of the output periodic signal based on the input voltage signal. Thus, the voltage-controlled oscillator 612 generates a reference signal Ss with a target frequency and outputs it to the amplifier 614 and the arithmetic unit 52. Furthermore, the voltage-controlled oscillator 612 is not limited to a VCO as long as it is an oscillator capable of adjusting the frequency of the output periodic signal.

[0113] Amplifier 614 has the function of controlling the amplitude of the output periodic signal according to the input control signal. Thus, amplifier 614 amplifies the input reference signal Ss, generates a drive signal Sd with the target amplitude, and outputs it to optical modulator 12.

[0114] 1.2. Arithmetic Unit

[0115] Figure 10 It is a detailed representation Figure 1 The diagram shows the arithmetic unit 52 in the function block diagram.

[0116] Figure 1 The arithmetic unit 52 shown includes a preprocessing unit 53, an orthogonal signal generation unit 57, a demodulation processing unit 55, a signal output unit 559, and a correction processing unit 62.

[0117] The arithmetic unit 52 performs demodulation processing on the sampled signal originating from the object 14, based on the optical detection signal output from the current-voltage converter 531. The sampled signal includes, for example, phase information and frequency information. Furthermore, the displacement of the object 14 can be obtained from the phase information, and the velocity of the object 14 can be obtained from the frequency information. Since different physical quantities can be obtained in this way, it can function as a displacement meter or a velocity meter; therefore, high functionality of the laser interferometer 1 can be achieved.

[0118] In the arithmetic unit 52, its circuit configuration is set according to the modulation processing method. In the laser interferometer 1 according to this embodiment, an optical modulator 12 equipped with a vibrating element 30 is used. The vibrating element 30 is a component that performs simple harmonic oscillation, and therefore its vibration speed changes constantly within the period. Therefore, the modulation frequency also changes with time, and existing demodulation circuits cannot be used directly.

[0119] Existing demodulation circuits refer to circuits that demodulate a sampled signal from a light detection signal containing a modulated signal modulated using an acousto-optic modulator (AOM). In an acousto-optic modulator, the modulation frequency does not change with time unless affected by external interference such as temperature variations. Therefore, existing demodulation circuits can demodulate a sampled signal from a light detection signal containing a modulated signal with a fixed modulation frequency, but they cannot directly demodulate a modulated signal containing a light modulated signal modulated by an optical modulator 12 whose modulation frequency changes (periodically) with time.

[0120] Therefore, as mentioned above, Figure 1 The arithmetic unit 52 shown includes a preprocessing unit 53, a quadrature signal generation unit 57, a demodulation processing unit 55, a signal output unit 559, and a correction processing unit 62. The photodetector signal output from the current-to-voltage converter 531 first passes through the preprocessing unit 53 and is then guided to the demodulation processing unit 55. Through this preprocessing, frequency modulation components are extracted from the photodetector signal to obtain a signal that can be demodulated using existing demodulation circuitry. Therefore, in the demodulation processing unit 55, the sampled signal originating from the object 14 is demodulated using a known demodulation method. Furthermore, in the quadrature signal generation unit 57, based on the reference signal Ss output from the signal generation unit 61 and the preprocessed signal S(t) output from the preprocessing unit 53, as shown... Figure 10 The diagram shows the generation of a cosine wave signal cos(θ) as an orthogonal signal. m (t) and the sinusoidal signal sin(θ) m (t)).

[0121] The aforementioned functions of the arithmetic unit 52 are implemented, for example, by hardware including a processor, memory, external interface, input unit, and display unit. Specifically, this is achieved by the processor reading and executing a program stored in memory. Furthermore, these components can communicate with each other via an internal bus.

[0122] Examples of processors include CPUs (Central Processing Units) and DSPs (Digital Signal Processors). Alternatively, instead of having these processors execute the software, the aforementioned functions can be implemented using FPGAs (Field-Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits).

[0123] Examples of storage devices include HDD (Hard Disk Drive), SSD (Solid State Drive), EEPROM (Electrically Erasable Programmable Read-Only Memory), ROM (Read-Only Memory), and RAM (Random Access Memory).

[0124] External interfaces include, for example, digital input / output ports such as USB (Universal Serial Bus) and Ethernet (registered trademark) ports.

[0125] As an input unit, examples include various input devices such as keyboards, mice, touch panels, and touchpads. As a display unit, examples include liquid crystal display panels and organic EL (Electroluminescence) display panels.

[0126] 1.2.1. Composition of the pretreatment unit

[0127] Figure 10 The preprocessing unit 53 shown includes a first bandpass filter 534, a second bandpass filter 535, a first delay adjuster 536, a multiplier 538, a third bandpass filter 539, a first AGC unit 540, a second AGC unit 541, and an adder 542. Furthermore, AGC stands for Auto Gain Control.

[0128] The optical detection signal output from the current-to-voltage converter 531 is split into two signals, a first signal S1 and a second signal S2, in the bifurcation section jp1. Figure 10 In this process, the path of the first signal S1 is set as the first signal path ps1, and the path of the second signal S2 is set as the second signal path ps2.

[0129] The first bandpass filter 534, the second bandpass filter 535, and the third bandpass filter 539 are filters that selectively allow signals within a specific frequency range to pass through.

[0130] The first delay adjuster 536 is a circuit that adjusts the delay of a signal using a memory that temporarily stores the signal. The multiplier 538 is a circuit that generates an output signal proportional to the product of the two input signals. The adder 542 is a circuit that generates an output signal proportional to the sum of the two input signals.

[0131] Next, the operation of the preprocessing unit 53 will be explained along the flow of the first signal S1 and the second signal S2.

[0132] After the first signal S1 passes through the first bandpass filter 534 configured on the first signal path ps1, its group delay is adjusted by the first delay adjuster 536. The group delay adjusted by the first delay adjuster 536 is equivalent to the group delay of the second signal S2 caused by the second bandpass filter 535 (described later). Through this delay adjustment, the delay time generated by the filter circuits passing through the first bandpass filter 534 through which the first signal S1 passes is made consistent between the second bandpass filter 535 and the third bandpass filter 539 through which the second signal S2 passes. The first signal S1, after passing through the first delay adjuster 536, is input to the adder 542 via the first AGC unit 540.

[0133] The second signal S2 is input to the multiplier 538 after passing through the second bandpass filter 535 configured on the second signal path ps2. In the multiplier 538, the second signal S2 is multiplied by the cosine wave signal cos(θ) output from the quadrature signal generation unit 57. m (t)). Then, after passing through the third bandpass filter 539, the second signal S2 is input to the adder 542 via the second AGC unit 541.

[0134] Adder 542 outputs a signal that is proportional to the sum of the first signal S1 and the second signal S2.

[0135] 1.2.2. Preprocessing

[0136] Next, the preprocessing in the preprocessing unit 53 will be explained. Preprocessing refers to the process of extracting the frequency modulation component from the optical detection signal. Furthermore, in the following explanation, as an example, consider a system where the frequency of the modulation signal varies sinusoidally, and the displacement of the object 14 also varies in simple harmonic motion along the optical axis. Here, E... m E d , Set as

[0137] [Formula 1]

[0138] E m =a m {cos(ω0t+B sinω m t+φ m )+i sin(ω0t+B sinω m t+φ m )} (1)

[0139] E d =a d {cos(ω0t+A sinω d t+φ d )+i sin(ω0t+A sinω d t+φ d (2)

[0140] φ=φ m -φ d (3)

[0141] At that time, the light detection signal I output from the current-to-voltage converter 531 PD Theoretically, it can be expressed by the following formula.

[0142] [Formula 2]

[0143] I PD =<|E m +E d | 2 >=<|Em 2 +E d 2 +2E m E d |>=a m 2 +a d 2 +2a m a d cos(B sinω m tA sinω d t+φ) (4)

[0144] In addition, E m E d , ω m ω d ω O a m a d As shown below.

[0145] [Formula 3]

[0146] E mElectric field components of the modulation signal originating from the optical modulator

[0147] E d Electric field components originating from the sampling signal of the object being measured.

[0148] φ m The initial phase of the modulation signal originating from the optical modulator.

[0149] φ d The initial phase originating from the sampling signal of the object being measured.

[0150] φ: Optical path phase difference of the laser interferometer

[0151] ω m Angular frequency of the modulation signal originating from the optical modulator

[0152] ω d : The angular frequency derived from the sampling signal of the object being measured

[0153] ω0: Angular frequency of the emitted light from the light source

[0154] a m :coefficient

[0155] a d :coefficient

[0156] In addition, in equation (4), <> represents time average.

[0157] The first and second terms of equation (4) above represent the DC component, and the third term represents the AC component. If this AC component is set as I... PD.AC , then I PD.AC As shown in the following formula.

[0158] [Formula 4]

[0159] I PD·AC =2a m a d cos(B sinω m tA sinω d t+φ)=2a m a d {cos(B sinω m t)cos(A sinω d t-φ)+sin(B sinω m t)sin(A sinω d t-φ)} (5)

[0160]

[0161]

[0162] A: Phase shift of the sampled signal

[0163] f dmax Doppler frequency shift of the sampled signal

[0164] f d Frequency of the sampled signal

[0165] B: Phase shift of the modulated signal

[0166] f mmax Doppler frequency shift of modulation offset

[0167] f m Frequency of the modulating signal

[0168] Here, we know that there are v-th degree Bessel functions as shown in equations (8) and (9).

[0169] [Formula 5]

[0170] cos{ζsin(2πf v t)}=J0(ζ)+2J2(ζ)cos(2·2πf v t)+2J4(ζ)cos(4·2πf ν t)+… (8)

[0171] sin{ζsin(2πf v t)}=2J1(ζ)sin(1·2πf v t)+2J3(ζ)sin(3·2πf v t)+… (9)

[0172] If we use the Bessel functions of equations (8) and (9) above to perform a series expansion of equation (5), it can be transformed as shown in equation (10) below.

[0173] [Formula 6]

[0174] I PD·AC =2a m a d [{J0(B)+2J2(B)cos(2·ω m t)+2J4(B)cos(4·ω m t)+…}cos(A sinω d t-φ)-{2J1(B)sin(1·ω m t)+2J3(B)sin(3·ω m t)+…}sin(A sinω d t-φ)] (10)

[0175] Where J0(B), J1(B), J2(B), ... are Bessel coefficients.

[0176] If the shape is modified as described above, then theoretically it can be said that the bandwidth corresponding to a specific number of passes can be extracted using a bandpass filter.

[0177] Therefore, in the aforementioned preprocessing unit 53, the AC component of the optical detection signal is preprocessed according to the following process based on this theory.

[0178] First, the amplitude of the AC component of the photodetector signal output from the current-to-voltage converter 531 is normalized by the ADC 532. The signal after passing through the ADC 532 is represented by the following equation (10-1).

[0179] [Formula 7]

[0180] I ADC_beat ={J0(B)+2J2(B)cos(2ω m t)+2J4(B)cos(4ω m t)+…}cos(A sinω d t-φ)-2{J0(B)+J1(B)sin(ω m t)+J3(B)sin(3ω m t)+…}sin(A sinω d t-φ) (101)

[0181] Furthermore, the signal after passing through ADC 532 is split into two signals, a first signal S1 and a second signal S2, at the bifurcation point jp1. The first signal S1 passes through a first bandpass filter 534. The center angular frequency of the first bandpass filter 534 is set to ω. m Therefore, the first signal S1 after passing through the first bandpass filter 534 is represented by the following formula.

[0182] [Formula 8]

[0183] I BPF1 =J1(B){-cos(ω m t+A sinω d t-φ)+cos(ω m tA sinω d t+φ)}=-2J1(B)sin(ω m t)·sin(A sinω d t-φ) (11)

[0184] On the other hand, the second signal S2 passes through the second bandpass filter 535. The center angular frequency of the second bandpass filter 535 is set to a value different from the center angular frequency of the first bandpass filter 534. Here, as an example, the center angular frequency of the second bandpass filter 535 is set to 2ω. m Therefore, the second signal S2 after passing through the second bandpass filter 535 is represented by the following formula.

[0185] [Formula 9]

[0186] I BPF2 =2J2(B)cos(2ω) m t)·cos(A sinω d t-φ) (12)

[0187] In multiplier 538, the second signal S2 after passing through the second bandpass filter 535 is multiplied by the cosine signal cos(θ) output from the quadrature signal generation unit 57 (described later). m (t)). The second signal S2 after passing through multiplier 538 is represented by the following formula.

[0188] [Formula 10]

[0189] I 538 =I BPF2 *cos(θ m (t))=2J2B)cos(2ω m t)·cos(A sinω d t-φ)·cos(ω m t-α)={J2(B)cos(A sinω d t-φ)}·{cos(3ωmt-α)+cos(ω m t+α)} (13)

[0190] In the above equation (13), α is the deviation magnitude, i.e., the phase difference, when the phase of the reference signal Ss deviates from its original phase. The original phase refers to the phase when the preprocessed signal S(t) output from the preprocessing unit 53 is a frequency-modulated signal or a signal based on it.

[0191] The second signal S2, after passing through multiplier 538, passes through third bandpass filter 539. The center angular frequency of third bandpass filter 539 is set to the same value as the center angular frequency of first bandpass filter 534. Here, as an example, the center angular frequency of third bandpass filter 539 is set to ω. m Therefore, the second signal S2 after passing through the third bandpass filter 539 is represented by the following formula.

[0192] [Formula 11]

[0193] I BPF3 =J2(B)cos(ω) m t+α)cos(A sinω d t-φ) (14)

[0194] Then, the first signal S1 represented by the above formula (11) has its phase adjusted by the first delay adjuster 536 and its amplitude adjusted by the first AGC unit 540.

[0195] Furthermore, the amplitude of the second signal S2, represented by the above equation (14), is also adjusted by the second AGC unit 541 so that the amplitude of the second signal S2 is consistent with the amplitude of the first signal S1. The first signal S1 after amplitude adjustment is represented by the following equation (14-1), and the second signal S2 after amplitude adjustment is represented by the following equation (14-2).

[0196] [Formula 12]

[0197] I AGC1 =-sin(ω) m t)·sin(A sinω d t-φ) (14-1)

[0198] I AGC2 =cos(ω m t+α)cos(A sinω d t-φ) (14-2)

[0199] Furthermore, the first signal S1 and the second signal S2 are added together by adder 542. The result of the addition is set as the preprocessing signal S(t). The preprocessing signal S(t) is represented by the following equation (15).

[0200] [Formula 13]

[0201] S(t)=I AGC1 +I AGC2 =-sin(ω) m t)·sin(A sinω d t-φ)+cos(ω m t+α)cos(A sinω d t-φ) (15)

[0202] As shown in equation (15) above, the preprocessed signal S(t) is represented by an expression containing the phase difference α. Therefore, when the phase difference α is an integer multiple of π, the above equation (15) is represented by the following equation (15-1).

[0203] [Formula 14]

[0204] S(t) = -sin(ω) mt)·sin(Asinω d t-φ)+cos(ω m t)cos(A sinω d t-φ)=cos(ω m t+A sinω d t-φ) (15-1)

[0205] In this specification, when the preprocessed signal S(t) is represented by the above equation (15-1), it is called "phase-consistent". On the other hand, when the preprocessed signal S(t) is represented by the above equation (15) and the phase difference α is not an integer multiple of π, it is called "phase-inconsistent".

[0206] When the phases are consistent, the preprocessed signal S(t) is represented by the above equation (15-1), and therefore can be considered a signal that only undergoes frequency modulation. In such a preprocessed signal S(t), since the frequency modulation component is extracted, the demodulation accuracy of the sampled signal in the demodulation processing unit 55 is improved. On the other hand, when the phases are inconsistent, the preprocessed signal S(t) can be considered a signal in which frequency modulation and amplitude modulation overlap. In such a preprocessed signal S(t), it is difficult to improve the demodulation accuracy of the sampled signal in the demodulation processing unit 55.

[0207] 1.2.3. Structure of the Orthogonal Signal Generation Unit

[0208] Figure 10 The quadrature signal generation unit 57 shown includes a fourth bandpass filter 571, a Hilbert transform filter 572, a second delay adjuster 573 (reference signal delayer), a reference signal phase operator 574, an absolute value operator 577, a third low-pass filter 578, a phase setting unit 579, an adder 580, a cosine generator 581, and a sine generator 582.

[0209] In this embodiment, based on the phase of the reference signal Ss and the amplitude of the preprocessed signal S(t), the quadrature signal generation unit 57 generates a cosine wave signal cos(θ) as mutually orthogonal waveforms. m (t) and the sinusoidal signal sin(θ) m (t)). In this specification, the process of generating such orthogonal waveforms is referred to as "orthogonal waveform generation process".

[0210] A signal generation unit 61 and an orthogonal signal generation unit 57 are arranged between them. Figure 1 The ADC533 is shown. The ADC533 is an analog-to-digital converter that converts analog signals into digital signals at a specified number of sampling bits. The fourth bandpass filter 571 is a filter that selectively allows signals within a specific frequency range to pass through.

[0211] Hilbert transform filter 572 performs Hilbert transform on the reference signal Ss to obtain signal i. The reference signal Ss output from voltage-controlled oscillator 612 is obtained by cos(ω m t) represents ω. m t is the angular frequency of the modulation signal of the optical modulator 12, and t is time. The Hilbert transform process is used to shift the phase of the reference signal Ss by π / 2.

[0212] The second delay adjuster 573 is a circuit that adjusts the delay of the signal using a memory that temporarily stores the signal, so that the reference signal Ss has the same delay as that generated by the Hilbert transform. Thus, signal r is obtained.

[0213] The reference signal phase operator 574 calculates the phase of the reference signal Ss based on the signal i output from the Hilbert transform filter 572 and the signal r output from the second delay adjuster 573. Specifically, it performs an arctangent operation on the ratio of signal i to signal r, i.e., an atan(i / r) operation.

[0214] The absolute value calculator 577 calculates the absolute value of the preprocessed signal S(t) output from the preprocessing unit 53. The third low-pass filter 578 is a filter that cuts off high-frequency signals based on the absolute value of the preprocessed signal S(t) output from the absolute value calculator 577.

[0215] The phase setting unit 579 has the functions of obtaining the envelope of the signal output from the third low-pass filter 578, obtaining the maximum and minimum values ​​(amplitude of the envelope) of the envelope, and outputting the phase quantity a.

[0216] The adder 580 outputs a signal proportional to the sum of the outputs from the reference signal phase operator 574 and the phase quantity setting unit 579. The cosine generator 581 generates a cosine wave signal cos(θ) based on the signal output from the adder 580. m (t)). The sine generator 582 generates a sine wave signal sin(θ) based on the signal output from the adder 580. m (t)).

[0217] 1.2.4. Orthogonal Waveform Generation Processing

[0218] In the orthogonal waveform generation process, firstly, the reference signal Ss is input to the fourth bandpass filter 571. The center angular frequency of the first bandpass filter 571 is set to ω. m The reference signal Ss output from the fourth bandpass filter 571 is split into two parts, one of which is input to the Hilbert transform filter 572, and the other is input to the second delay adjuster 573.

[0219] Hilbert transform filter 572 shifts the phase of reference signal Ss by π / 2, generating signal i. Second delay adjuster 573 delays reference signal Ss, generating signal r. Signals i and r are input to reference signal phase operator 574.

[0220] The reference signal phase operator 574 performs an atan(i / r) operation to obtain the phase of the reference signal Ss. The phase of the reference signal Ss is then input to the adder 580.

[0221] The absolute value operator 577 acquires the absolute value of the preprocessed signal S(t). This allows the waveform of the negative side of the preprocessed signal S(t) to be converted to the positive side and synthesized. The signal from the absolute value operator 577 is input to the third low-pass filter 578.

[0222] The third low-pass filter 578 cuts off signals in the high-frequency range. This allows for easy and high-precision acquisition of the envelope in the phase setting unit 579. The signal from the third low-pass filter 578 is input to the phase setting unit 579.

[0223] The phase setting unit 579 sets the phase amount 'a' to be added to the calculation result atan(i / r) in the adder 580 based on the signal from the third low-pass filter 578. In other words, the quadrature signal generation unit 57 adjusts the phase of the reference signal Ss. The setting method will be described later.

[0224] In adder 580, the sum of the output from reference signal phase operator 574 and the output from phase quantity setting unit 579 is calculated. Here, the sum is set as β. β is a + atan(i / r). Furthermore, cosine generator 581 generates a cosine wave signal cos(θ). m (t)), the sine generator 582 generates a sine wave signal sin(θ). m (t)). Cosine wave signal cos(θ) m (t) is output to the multiplier 538 and the demodulation processing unit 55 (described later), and a sine wave signal sin(θ) is generated. m (t)) is output toward the demodulation processing unit 55. Furthermore, θ m (t) is ω m t-β.

[0225] 1.2.5. Phase Quantity Setting Method

[0226] In the phase setting unit 579, when the phases are inconsistent, the phase amount 'a' added by the adder 580 is set in a manner that minimizes the influence of the amplitude modulation described above. Consequently, in the cosine generator 581 and the sine generator 582, a cosine wave signal cos(θ) based on the phase amount 'a' is generated. m (t) and the sinusoidal signal sin(θ)m (t)). Therefore, the cosine wave signal cos(θ) m The amplitude modulation effect in the preprocessed signal S(t) is reduced by multiplier 538. Furthermore, it ultimately achieves phase synchronization. Additionally, when the phases are synchronized, the cosine wave signal cos(θ)... m (t) and the sinusoidal signal sin(θ) m When the preprocessed signal S(t) is input to the demodulation processing unit 55, it can be demodulated with high precision.

[0227] Figure 11 It means Figure 10 The flowchart shows an example of a method for setting the phase quantity using the phase quantity setting unit 579. Figure 11 The phase quantity setting shown is preferably performed using a standard sample vibrating at a single frequency as the object 14. Therefore, the phase quantity setting unit 579 can more accurately determine the phase quantity 'a' to be added in the adder 580. Figure 11 In the phase quantity setting method shown, the amplitude of the preprocessed signal S(t) is repeatedly evaluated while the value of the phase quantity a is gradually changed. Furthermore, the phase quantity a at which the amplitude falls below a predetermined value is stored in memory as the optimal value. Moreover, after determining the optimal phase quantity a, it is sufficient to fix the phase quantity a.

[0228] therefore, Figure 11 The phase setting method shown is performed, for example, using the aforementioned standard sample before measuring the object 14 using the laser interferometer 1. This allows for automatic calibration of the laser interferometer 1. Examples of standard samples include piezoelectric elements or quartz oscillators.

[0229] exist Figure 11 In the illustrated process S102, firstly, the sign function sgn and the phase quantity a are initialized. Specifically, the value 1 is input into the sign function sgn, and the value a0 is input into the phase quantity a. The value a0 can be any value.

[0230] In step S104, the envelope of the preprocessed signal S(t) is obtained via the absolute value arithmetic unit 577 and the third low-pass filter 578. Furthermore, in step S104, the maximum and minimum values ​​of the envelope are obtained, and the difference dS0 between the maximum and minimum values ​​is stored in memory. This difference dS0 corresponds to the amplitude of the preprocessed signal S(t).

[0231] In process S106, the phase quantity a is updated in the phase quantity setting unit 579 using the formula a + sgn * Δa → a, and set as the output value. This formula means that, based on the two possible values ​​of the sign function sgn, namely 1 or -1, a small amount Δa is added to or subtracted from the current value of the phase quantity a to obtain the new phase quantity a. The small amount Δa is not particularly limited as long as it is smaller than the phase quantity a. The updated phase quantity a is output to the adder 580. Then, in the quadrature signal generation unit 57, the phase of the reference signal Ss is changed according to the new phase quantity a set by the phase quantity setting unit 579, and a cosine wave signal cos(θ) is generated based on the updated reference signal Ss. m (t) and the sinusoidal signal sin(θ) m (t)). Furthermore, in the preprocessing unit 53, based on the cosine wave signal cos(θ) m (t) generates a new preprocessed signal S(t).

[0232] In step S108, for the new preprocessed signal S(t), the difference between the maximum and minimum values ​​of the envelope is obtained in the same manner as in step S104 and stored in memory. In step S108, this difference is set as dS1.

[0233] In step S110, it is determined whether the difference dS1 is below a predetermined value. The predetermined value is, for example, the difference between the maximum and minimum values ​​of the envelope when the preprocessed signal S(t) is considered to be only a frequency-modulated signal. Therefore, when the difference dS1 is below the predetermined value, it can be determined that the current phase quantity a is optimal. Therefore, this process ends. On the other hand, when the difference dS1 is greater than the predetermined value, it can be determined that the current phase quantity a is not optimal, and therefore the process proceeds to step S112.

[0234] In step S112, the number of times the judgment in step S110 was performed is obtained. Furthermore, it is determined whether the number of times obtained is greater than a predetermined number. The predetermined number is, for example, the actual value of the number of repetitions when the optimal phase value a is determined by repeatedly evaluating the amplitude of the preprocessed signal S(t) while gradually changing the value of the phase quantity a, as described above. Specifically, the maximum value among these actual values ​​can be used as the predetermined number. Specific examples of the number of repetitions include the number of times the phase quantity a was updated.

[0235] When the number of times obtained exceeds a predetermined number, it can be determined that it is difficult to determine the optimal phase value 'a', and the process proceeds to step S114. In step S114, the phase value setting unit 579 issues an error. In this case, simply displaying an error message on the aforementioned display unit prompts the user to take action, such as changing the standard sample. After issuing the error, the process ends. On the other hand, when the number of times obtained is less than the predetermined number, the process proceeds to step S116.

[0236] In step S116, it is determined whether the difference dS1 < difference dS0 holds true. If it does, it can be determined that the influence of amplitude modulation in the new preprocessed signal S(t) has been reduced. Furthermore, it can be determined that the value of the sign function sgn during initialization in step S102 is appropriate. In this case, the process proceeds to step S118. In step S118, the current value of difference dS1 is input to difference dS0. Then, the process returns to step S106. In the second step S106, the phase quantity a is updated again using the formula a + sgn * Δa → a. Regarding the sign function sgn in this formula, since the determination that it is appropriate has already been passed, it is set to remain unchanged. Furthermore, in the preprocessing unit 53, a new preprocessed signal S(t) reflecting the updated phase quantity a is generated.

[0237] In the second step S108, the difference between the maximum and minimum values ​​of the envelope of the new preprocessed signal S(t) is obtained and stored in memory. The difference dS1 obtained in the second step S108 is smaller than the difference dS1 obtained in the first step S108. Therefore, for the new preprocessed signal S(t), the influence of amplitude modulation is further reduced, approaching that of a signal with only frequency modulation.

[0238] On the other hand, in step S116, when the difference dS1 < difference dS0 is not true, that is, when difference dS1 ≥ difference dS0, it can be determined that the reduction in amplitude modulation effect was not confirmed in the new preprocessed signal S(t). Additionally, it can be determined that the value of the sign function sgn during initialization in step S102 is inappropriate. In this case, proceed to step S120.

[0239] In step S120, the sign function sgn is reversed with the current value. That is, the value obtained by multiplying the current value by -1 is input into the new sign function sgn. Then, the process moves to step S118.

[0240] Following this process, as long as no error is detected, the phase quantity a, the preprocessed signal S(t), and the difference dS0 are repeatedly updated until the difference dS1 falls below a predetermined value. As a result, the phase quantity a is adjusted in the phase quantity setting unit 579 until the preprocessed signal S(t) is considered a frequency-modulated signal only, and a cosine wave signal cos(θ) as an orthogonal signal is generated based on the phase-adjusted reference signal Ss. m (t) and the sinusoidal signal sin(θ) m (t)).

[0241] By generating the cosine wave signal cos(θ) in this way mBy inputting the preprocessing signal S(t) into the preprocessing unit 53, the preprocessed signal S(t) can be brought closer to its original phase. As a result, the laser interferometer 1 can be calibrated. Moreover, after calibration, the object 14 can be measured using only the obtained optimal phase value a. This improves the accuracy of demodulating the sampled signal from the optical detection signal, thereby enabling high-precision measurement of the object 14. Furthermore, the calibration of the laser interferometer 1 described above can be performed at any time and at any frequency.

[0242] The quadrature signal generation unit 57 and the phase setting method have been explained above. However, if the phase of the preprocessed signal S(t) is originally consistent and does not require correction, the quadrature signal generation unit 57 can be omitted. In this case, the reference signal Ss and the signal whose phase is shifted by π / 2 can be used as the quadrature signal.

[0243] 1.2.6. Composition of the demodulation processing unit

[0244] The demodulation processing unit 55 performs demodulation processing on the sampled signal originating from the object 14 from the preprocessed signal S(t). There are no particular limitations on the demodulation processing method; a well-known method such as quadrature detection can be used. Quadrature detection is a method of demodulation processing that involves mixing mutually orthogonal signals from the outside into the input signal.

[0245] Figure 10 The demodulation processing unit 55 shown is a digital circuit that includes a multiplier 551, a multiplier 552, an inverting amplifier 553, a first low-pass filter 555, a second low-pass filter 556, a divider 557, and an arctangent operator 558.

[0246] Multipliers 551 and 552 are circuits that generate an output signal proportional to the product of the two input signals. Inverting amplifier 553 is a circuit that generates an output signal with a gain of -1, no amplitude change, and which inverts the phase of the input signals. The first low-pass filter 555 and the second low-pass filter 556 are filters that cut off signals in the high-frequency range.

[0247] Divider 557 is a circuit that generates an output signal proportional to the quotient of the two input signals. Arctangent calculus 558 is a circuit that outputs the arctangent of the input signals. The output signal from arctangent calculus 558 is fed into input signal output section 559.

[0248] The signal output unit 559 calculates the phase obtained by the arctangent arithmetic unit 558. Calculate the phase The information originates from the object 14. Furthermore, the signal output unit 559 performs phase connection when there is a 2π phase transition between adjacent points through phase expansion processing. Moreover, the displacement of the object 14 is calculated based on the obtained phase information. Thus, a displacement meter is implemented. Additionally, the velocity of the object 14 can be determined from the displacement. Thus, a speed meter is implemented.

[0249] Furthermore, the demodulation processing unit 55 is not limited to digital circuits, but can also be an analog circuit. The analog circuit may also include an F / V converter circuit or a ΔΣ counter circuit.

[0250] Furthermore, the frequency information originating from the object 14 can also be calculated in the aforementioned signal output unit 559. The speed of the object 14 can be calculated based on the frequency information.

[0251] 1.2.7. Demodulation Processing

[0252] In the demodulation process, firstly, the preprocessed signal S(t) is split into two parts using the bifurcation part jp2. In multiplier 551, one of the split signals is multiplied by the sine wave signal sin(θ) output from sine generator 582 via inverting amplifier 553. m (t)). That is, in multiplier 551, the preprocessed signal S(t) is mixed to make the sine wave signal sin(θ) m The phase-inverted signal of (t) is -sin(θ) m (t)). In multiplier 552, the divided signal is multiplied by the cosine signal cos(θ) output from cosine generator 581. m (t)). That is, in multiplier 552, the preprocessed signal S(t) is mixed with the cosine wave signal cos(θ). m (t)).

[0253] The signal passing through multiplier 551 passes through second low-pass filter 555 and is then input as signal y into divider 557. The signal passing through multiplier 552 passes through second low-pass filter 556 and is then input as signal x into divider 557. Furthermore, in this specification, signals x and y are collectively referred to as "mixed signals". In divider 557, a division operation is performed between signal y and signal x, and the output y / x is passed through arctangent operator 558 to obtain the result atan(y / x). Thus, the phase information of the sampled signal is obtained.

[0254] Then, by inputting the calculation result atan(y / x) into the signal output unit 559, the displacement or velocity of the object 14 is output.

[0255] Figure 12 It means according to Figure 11The illustrated process shows an example of the waveforms of the preprocessed signal S(t) before the laser interferometer 1 is calibrated, the phase information after demodulation by the demodulation processing unit 55 (phase information before expansion), and the phase information after phase expansion processing by the signal output unit 559 (phase information after expansion).

[0256] like Figure 12 As shown, the amplitude of the preprocessed signal S(t) before correction changes significantly, becoming a signal with overlapping frequency modulation and amplitude modulation. Therefore, the amplitude of the envelope of the preprocessed signal S(t) also increases. Therefore, in Figure 12 In the unwound phase information shown, irregular waveforms are generated at the locations indicated by the arrows, and the waveforms of the unwound phase information become discontinuous. In this case, it is difficult to accurately determine the displacement of object 14 based on the unwound phase information.

[0257] Figure 13 It means according to Figure 11 The process shown is an example of the waveforms of the preprocessed signal S(t) after correction by the laser interferometer 1, the phase information after demodulation by the demodulation processing unit 55 (phase information before expansion), and the phase information after phase expansion processing by the signal output unit 559 (phase information after expansion).

[0258] like Figure 13 As shown, the amplitude change of the preprocessed signal S(t) after correction is small, almost becoming a frequency-modulated signal. Therefore, the amplitude of the envelope of the preprocessed signal S(t) also decreases. Therefore, in Figure 13 No irregular waveforms were generated in the phase information before expansion shown. Additionally, Figure 13 The waveform of the expanded phase information shown becomes a continuous waveform. In this case, the displacement of the object 14 can be calculated with high precision based on the expanded phase information.

[0259] 1.2.8. Calibration Processing Department

[0260] like Figure 1 As shown, the reference signal Ss output from the signal generation unit 61 and the output signal Sm output corresponding to the drive of the optical modulator 12 are input to the correction processing unit 62. Furthermore, the correction processing unit 62 outputs a frequency control signal Sf1 (correction signal) to the voltage-controlled oscillator 612. Then, the correction processing unit 62 outputs an amplification control signal Sam (correction signal) to the amplifier 614.

[0261] The correction processing unit 62 is mounted, for example, on an FPGA, and preferably located on the sensor head 51. This reduces the physical distance between the correction processing unit 62 and the optical modulator 12, and suppresses the decrease in the S / N ratio of the output signal Sm caused by electromagnetic noise, for example.

[0262] Figure 14 It is a detailed representation Figure 1 The diagram shows the correction processing unit 62 in the functional block diagram.

[0263] The output signal Sm from the optical modulator 12 is input Figure 14 The first offset removal unit 631 is shown. The first offset removal unit 631 has the function of removing the DC (direct current) component and extracting the AC (alternating current) component. The output signal Sm after passing through the first offset removal unit 631 is input to the correction processing unit 62.

[0264] The reference signal Ss from the voltage-controlled oscillator 612 is input. Figure 14 The second offset removal unit 632 is shown. The second offset removal unit 632 has the function of removing the DC (direct current) component and extracting the AC (alternating current) component. The reference signal Ss after passing through the second offset removal unit 632 is input to the correction processing unit 62 and ADC 533.

[0265] Figure 14 The correction processing unit 62 shown includes an absolute value arithmetic unit 621, a multiplier 622, a multiplier 623, a fourth low-pass filter 624, a fifth low-pass filter 625, an amplitude gain setting unit 626, and a frequency setting unit 627.

[0266] The absolute value calculator 621 calculates the absolute value of the output signal Sm that has passed through the first offset removal unit 631.

[0267] Multipliers 622 and 623 are circuits that output a signal proportional to the product of two input signals. In multiplier 622, both input signals are the output signal Sm. Therefore, multiplier 622 outputs a signal proportional to the square of the output signal Sm. Conversely, in multiplier 623, the two input signals are the output signal Sm and the reference signal Ss. Therefore, multiplier 623 outputs a signal proportional to the product of the output signal Sm and the reference signal Ss.

[0268] Multipliers 622 and 623 can use components such as Gilbert units, or they can be circuits that perform addition and subtraction operations on two input signals after logarithmic transformation using operational amplifiers, and then perform inverse logarithmic transformation.

[0269] The fourth low-pass filter 624 and the fifth low-pass filter 625 are filters that cut off signals in the high-frequency range of the input signal. The transmission bandwidth of the fourth low-pass filter 624 and the fifth low-pass filter 625 only needs to be a bandwidth that can remove more than twice the frequency of the driving signal Sd, and preferably a bandwidth that can remove more than the frequency of the driving signal Sd.

[0270] The signal output from multiplier 622 and passing through the fourth low-pass filter 624 becomes, as described below, a signal with a value corresponding to the amplitude of the output signal Sm. The amplitude gain setting unit 626 has the function of determining the amplitude (target amplitude) to be set for the drive signal Sd based on this signal. Furthermore, the amplitude gain setting unit 626 controls the gain (amplification rate) set by the amplifier 614 of the signal generation unit 61 to make the amplitude of the drive signal Sd the target amplitude. As control logic, feedback control such as PI control or PID control can be cited as an example. The amplitude gain setting unit 626 outputs an amplification rate control signal Sam corresponding to the gain to be set to the amplifier 614.

[0271] In amplifier 614, the amplitude of the drive signal Sd is amplified according to the amplification control signal Sam. As a result, the amplitude of the drive signal Sd is corrected.

[0272] The signal output from multiplier 623 and input to fifth low-pass filter 625 becomes, as described below, a signal having a value corresponding to the phase difference between the output signal Sm and the reference signal Ss. Here, the phase of the output signal Sm corresponds to the phase of the drive signal Sd. Furthermore, the phase of the drive signal Sd corresponds to the phase of the reference signal Ss. Therefore, the frequency setting unit 627 has the function of determining the frequency (target frequency) to be set for the reference signal Ss. Moreover, the frequency setting unit 627 controls the voltage set by the voltage-controlled oscillator 612 of the signal generation unit 61 to make the frequency of the reference signal Ss the target frequency. As control logic, feedback control such as PI control or PID control can be cited as an example. The frequency setting unit 627 outputs a frequency control signal Sf1 corresponding to the frequency to be set to the voltage-controlled oscillator 612.

[0273] In the voltage-controlled oscillator 612, a reference signal Ss with a frequency corresponding to the frequency control signal Sf1 is generated. As a result, the frequency of the reference signal Ss is corrected. Furthermore, the frequency of the drive signal Sd is also corrected as a result.

[0274] 1.2.9. Acquisition of the output signal from the optical modulator

[0275] Figure 15 This is a diagram illustrating an example of a circuit for acquiring the output signal Sm from the optical modulator 12.

[0276] The output signal Sm can be a signal obtained by detecting the current flowing in the vibrating element 30 of the optical modulator 12, or a signal obtained by detecting the voltage applied to the vibrating element 30. For example, if the signal obtained by detecting the current flowing in the vibrating element 30 is set as the output signal Sm, such as... Figure 15 As shown, the current value flowing in the vibrating element 30 is detected using a current shunt monitor 64. Figure 15 The current shunt monitor 64 shown has a shunt resistor 641 and an operational amplifier 642, which converts the current flowing in the vibrating element 30 into a voltage value and detects it. This yields an output signal Sm as a voltage signal. The obtained output signal Sm is converted into a digital signal in the ADC 643 and output to the first offset removal unit 631.

[0277] In addition to the methods described above, other methods for detecting the current flowing in the vibrating element 30 include using a Hall element and detecting the electromotive force by winding a coil in the current path.

[0278] 1.2.9. Correction Processing

[0279] Next, the correction processing in the correction processing unit 62 will be explained. The correction processing refers to correcting the drive signal Sd and the reference signal Ss by changing the set values ​​of the voltage control oscillator 612 and the amplifier 614 according to the correction signal output from the correction processing unit 62.

[0280] In the case that the output signal Sm from the optical modulator 12 is, for example, a voltage signal, the previous output signal Sm from the first offset removal unit 631 is represented by the following equation (16).

[0281] [Formula 15]

[0282] C QOM =A m sin(ω m t+α m1 )+o QOM (16)

[0283] In the above equation (16), V QOM This is the voltage value of the output signal Sm. Additionally, A... m It is the coefficient corresponding to the amplitude of the output signal Sm, α m1 It is the phase difference between the output signal Sm and the reference signal Ss, and satisfies -π / 2 < α. m1 <π / 2. Therefore, O QOM It is the DC component of the output signal Sm.

[0284] Therefore, the output signal Sm after passing through the first offset removal unit 631 is represented by the following equation (16-1).

[0285] [Formula 16]

[0286] C QOM =A m sin(ω m t+α m1 (16-1)

[0287] On the other hand, the reference signal Ss from the second offset removal unit 632 is represented by the following equation (18).

[0288] [Formula 17]

[0289] V OSC =v OSC cos(ω m t)+O OSC (18) In the above equation (18), V OSC This is the voltage value of the reference signal Ss. Additionally, v OSC It is the coefficient corresponding to the amplitude of the reference signal Ss, O OSC It is the DC component of the reference signal Ss.

[0290] Therefore, the reference signal Ss after passing through the second offset removal section 632 is represented by the following equation (18-1).

[0291] [Formula 18]

[0292] V OSC =c OSC cos(ω m t) (18-1)

[0293] The output signal Sm, which has passed through the first offset removal unit 631, is divided into two. Furthermore, one of the output signals Sm is squared by the multiplier 622 after passing through the absolute value arithmetic unit 621, and the result is represented by the following equation (16-2).

[0294] [Formula 19]

[0295]

[0296] Then, it passes through the fourth low-pass filter 624, thereby extracting only the first term on the right side of the above equation (16-2). Thus, the output signal Sm after passing through the fourth low-pass filter 624 is represented by the following equation (16-3).

[0297] [Formula 20]

[0298]

[0299] As shown in equation (16-3) above, the input signal V input to the amplitude gain setting unit 626 is... QOM 2 This becomes a signal that does not change over time. Therefore, in the amplitude gain setting unit 626, for the output signal Sm represented by the above equation (16-3), the coefficient A, which is the target, is set. m The value obtained by substituting into equation (16-3) above is used as the control target value for feedback control. Furthermore, the amplification control signal Sam corresponding to the control target value is output to the amplifier 614 of the signal generation unit 61. As a result, the gain of the amplitude in the amplifier 614 can be changed to correct the amplitude of the drive signal Sd to the target amplitude.

[0300] In multiplier 623, the output signal Sm of the other side, which has been divided into two, is multiplied by the reference signal Ss. Thus, the signal output from multiplier 623 is represented by the following equation (17-2).

[0301] [Formula 21]

[0302]

[0303] Then, it passes through the fifth low-pass filter 625, thereby extracting only the first term on the right side of the above equation (17-2). Thus, the output signal Sm after passing through the fifth low-pass filter 625 is represented by the following equation (17-3).

[0304] [Formula 22]

[0305]

[0306] As shown in equation (17-3) above, the input signal V input to the frequency setting unit 627 QOM ·V OSC The right side includes coefficient A. m coefficient v OSC and phase difference α m1 The signal. Where, coefficient v OSC It is known. On the other hand, coefficient A m Satisfy 0 < A m As described above, it is controlled to converge to the coefficient A, which is the objective. m Therefore, the input signal V QOM ·V OSC This also becomes a signal that does not change over time. Therefore, in the frequency setting unit 627, for example, the phase difference α that is targeted is used... m1The value obtained by substituting into equation (17-3) above is used as the control target value for feedback control. Furthermore, a frequency control signal Sf1 corresponding to the control target value is output to the voltage-controlled oscillator 612 of the signal generation unit 61. This allows the frequency of the reference signal Ss output from the voltage-controlled oscillator 612 to be changed, correcting the frequency of the reference signal Ss to the target frequency. Additionally, the frequency of the drive signal Sd can also be corrected to the target frequency.

[0307] Furthermore, the phase difference α as the target m1 For example, in a vibrating element 30 that vibrates at a mechanical resonant frequency, the phase difference between the driving signal Sd and the output signal Sm can be determined. Specifically, it is known that in such a vibrating element 30, the phase of the output signal Sm is delayed by approximately 90 degrees [deg] relative to the input driving signal Sd. Furthermore, during the process until the output signal Sm is input to the correction processing unit 62, a phase delay δ [deg] may sometimes occur. Taking these factors into account, the target phase difference α... m1 For example, it can be 90 + δ[deg]. The phase delay δ can be determined experimentally or through simulation.

[0308] Furthermore, when temperature changes occur, the mechanical resonant frequency sometimes changes, and the efficiency of the vibrating element 30 in converting the input power into vibration changes. When this conversion efficiency changes, the amplitude of the vibration of the vibrating element 30 changes. Therefore, in the correction process, firstly, the frequency of the reference signal Ss and the frequency of the drive signal Sd are corrected first. Then, the amplitude of the drive signal Sd is corrected as needed. By performing the correction process in this order, the aforementioned frequency and amplitude can be efficiently controlled to the target values.

[0309] Furthermore, based on the control in the frequency setting unit 627 described above, it is preferable to make the control of the signal input to the amplitude gain setting unit 626 converge earlier than the control of the signal input to the frequency setting unit 627. Therefore, since instability of the target control value in the frequency setting unit 627 is suppressed, instability in the correction process can be prevented.

[0310] Furthermore, the amplitude gain setting unit 626 and the frequency setting unit 627 are respectively constructed by combining operational amplifiers, etc., to perform feedback control operations such as PID control. In this case, in order to make the control of the signal input to the amplitude gain setting unit 626 converge earlier than the control of the signal input to the frequency setting unit 627, it is only necessary to set the crossover frequency of the open-loop transfer function of the control loop in the operation of the amplitude gain setting unit 626 to be higher than the crossover frequency of the open-loop transfer function of the control loop in the operation of the frequency setting unit 627.

[0311] By performing the above correction process, the following results can be obtained.

[0312] When the mechanical resonant frequency of the vibrating element 30 changes due to external disturbances such as ambient temperature variations, gravity variations, vibrations, and noise, the frequency or amplitude of the vibration of the vibrating element 30 changes, and the S / N ratio of the modulated signal decreases. This results in a reduction in the demodulation accuracy of the sampled signal.

[0313] In contrast, by performing the correction process described above, the frequency and amplitude of the vibration of the vibrating element 30 can be kept constant even when external disturbances such as temperature changes are applied. In other words, even when external disturbances such as temperature changes are applied, the frequency or amplitude of the vibration of the vibrating element 30 can be corrected to remain unchanged. This suppresses the decrease in the S / N ratio of the modulation signal. As a result, even when external disturbances such as temperature changes are applied, the accuracy of the preprocessing or demodulation processing in the arithmetic unit 52 can be improved, thereby suppressing the decrease in the demodulation accuracy of the sampled signal.

[0314] Furthermore, even when external disturbances such as temperature changes cause a shift in the mechanical resonant frequency, the frequency of the drive signal Sd can follow this shift. Therefore, the vibrating element 30 can be continuously driven near its mechanical resonant frequency. This improves the driving efficiency of the vibrating element 30, thus enabling lower power consumption in the laser interferometer 1. Moreover, when the vibrating element 30 is driven, for example, by an oscillation circuit, it is difficult to drive it near its mechanical resonant frequency. This is because the circuit configuration of the oscillation circuit is impractical due to various constraints.

[0315] 1.2.10. Effects of the first implementation method

[0316] As described above, the laser interferometer 1 according to this embodiment includes a laser source 2, an optical modulator 12, a light-receiving element 10, a calculation unit 52, and a signal generation unit 61. The laser source 2 emits outgoing light L1 (laser). The optical modulator 12 includes a vibrating element 30 driven by a drive signal Sd, and the vibrating element 30 is used to overlap the modulation signal with the outgoing light L1. The light-receiving element 10 receives object light L3 (laser containing a sampled signal) and reference light L2 (laser containing a modulation signal) that are superimposed by reflection from an object 14, and outputs a received light signal. The calculation unit 52 performs calculations on the received light signal based on a reference signal Ss. The signal generation unit 61 outputs the drive signal Sd and the reference signal Ss.

[0317] Furthermore, the arithmetic unit 52 includes a preprocessing unit 53, a demodulation unit 55, and a correction unit 62. The preprocessing unit 53 performs preprocessing to extract frequency modulation components from the received light signal, outputting a preprocessed signal S(t) containing the frequency modulation components. The demodulation unit 55 mixes the preprocessed signal S(t) with orthogonal signals to obtain signals x and y (mixed signals), and then demodulates the sampled signal from signals x and y. The correction unit 62 outputs an amplification control signal Sam and a frequency control signal Sf1 as correction signals based on the output signal Sm output corresponding to the drive of the vibrating element 30. Moreover, the signal generation unit 61 corrects the drive signal Sd and the reference signal Ss based on the amplification control signal Sam and the frequency control signal Sf1.

[0318] In this configuration, even under external interference such as temperature changes, the frequency or amplitude of the drive signal Sd can follow the changes in the mechanical resonant frequency or vibration amplitude of the vibrating element 30. Therefore, the frequency and amplitude of the vibration of the vibrating element 30 can be kept constant. As a result, the decrease in the S / N ratio of the modulation signal can be suppressed, and the decrease in the demodulation accuracy of the sampled signal can be suppressed. Thus, a laser interferometer 1 capable of measuring the displacement or velocity of the object 14 with high accuracy even under external interference can be realized. Furthermore, by using the signal generation unit 61 and the correction processing unit 62, the vibrating element 30 can be driven near its mechanical resonant frequency, thereby achieving low power consumption in the laser interferometer 1.

[0319] Furthermore, the correction processing unit 62 is preferably configured to correct the frequency of the reference signal Ss and the frequency of the drive signal Sd based on the phase difference between the output signal Sm and the reference signal Ss.

[0320] With this configuration, the phase difference between the output signal Sm, which corresponds to the drive of the optical modulator 12, and the reference signal Ss can be fed back to the aforementioned frequency. Since the phase difference between the output signal Sm and the reference signal Ss directly reflects the influence of external interference on the modulated signal, it is suitable as an input signal for feedback control. Therefore, with the above configuration, the influence of external interference can be corrected in real time, and a laser interferometer 1 with particularly high resistance to external interference can be realized.

[0321] Furthermore, the correction processing unit 62 is preferably configured to correct the amplitude of the drive signal Sd based on the amplitude of the output signal Sm.

[0322] With this configuration, the amplitude of the output signal Sm, which corresponds to the drive of the optical modulator 12, can be fed back to the amplitude of the drive signal Sd. Since the amplitude of the output signal Sm directly reflects the influence of external interference on the modulated signal, it is suitable as an input signal for feedback control. Therefore, with the above configuration, the influence of external interference can be corrected in real time, and a laser interferometer 1 with particularly high resistance to external interference can be realized.

[0323] Additionally, the signal generation unit 61 includes a voltage-controlled oscillator 612 and an amplifier 614. The voltage-controlled oscillator 612 generates a reference signal Ss. The amplifier 614 adjusts the amplitude of the reference signal Ss and outputs it as a drive signal Sd.

[0324] With this configuration, amplifier 614 generates a drive signal Sd based on a reference signal Ss generated by voltage-controlled oscillator 612. Therefore, signal generation unit 61 can correct the frequency of the reference signal Ss and the frequency of the drive signal Sd respectively based on frequency control signal Sf1. Furthermore, the amplitude of the drive signal Sd can be corrected independently based on amplification control signal Sam.

[0325] Furthermore, in this embodiment, a voltage-controlled oscillator 612 is used as the oscillator in the signal generation unit 61. Therefore, a general-purpose voltage-controlled oscillator 612 can be used, thus easily reducing the cost of the signal generation unit 61.

[0326] Furthermore, as described above, the vibrating element 30 is preferably a quartz oscillator. This allows for the generation of a high-precision modulation signal using the extremely high Q value of quartz. Consequently, the sampled signal originating from the object 14 can be demodulated with even higher precision. Examples of quartz oscillators include AT-cut quartz oscillators, SC-cut quartz oscillators, and tuning fork quartz oscillators.

[0327] Furthermore, in this embodiment, the quadrature signal generation unit 57 generates the aforementioned quadrature signal based on the phase of the reference signal Ss and the amplitude of the preprocessed signal S(t). Furthermore, the quadrature signal generation unit 57 adjusts the phase of the reference signal Ss based on the amplitude of the preprocessed signal S(t). Moreover, it uses the cosine wave signal cos(θ) as the adjusted signal... m The input preprocessing unit 53 can make the preprocessed signal S(t) close to the frequency-modulated signal, which can improve the accuracy of demodulating the sampled signal from the object 14 from the light-receiving signal.

[0328] With this configuration, even if the phase of the reference signal Ss deviates from its original phase, it can be corrected. Therefore, a laser interferometer 1 capable of measuring the displacement or velocity of the object 14 with high precision can be realized.

[0329] Furthermore, in this embodiment, the quadrature signal generation unit 57 includes a phase amount setting unit 579 that sets the phase of the quadrature signal based on the amplitude of the preprocessed signal S(t). As described above, the phase amount setting unit 579 has the function of setting the phase amount a to be added by the adder 580. Moreover, the quadrature signal generation unit 57 adjusts the phase of the reference signal Ss according to the phase amount a to generate the quadrature signal, i.e., the cosine wave signal cos(θ). m (t) and the sinusoidal signal sin(θ) m (t)). This quadrature signal is mixed with the preprocessed signal S(t) in the demodulation processing unit 55. By appropriately setting the phase amount a, the phase of the preprocessed signal S(t) can be made to match that of the quadrature signal. As a result, demodulation processing from the preprocessed signal S(t) can be performed with high precision in the demodulation processing unit 55.

[0330] In addition, in this embodiment, the phase setting unit 579 sets the phase of the quadrature signal in such a way that the difference between the maximum value of the amplitude of the preprocessed signal S(t) and the minimum value of the amplitude of the preprocessed signal S(t) is less than or equal to a predetermined value.

[0331] Therefore, the optimal phase value a can be efficiently found in the phase value setting unit 579 so that the preprocessed signal S(t) becomes a frequency-modulated signal or a signal based on that.

[0332] In this embodiment, the quadrature signal generation unit 57 includes a Hilbert transform filter 572, a second delay adjuster 573 (reference signal delayer), and a reference signal phase operator 574. The Hilbert transform filter 572 performs a Hilbert transform on the reference signal Ss to obtain signal i. The second delay adjuster 573 delays the reference signal Ss to obtain signal r. The reference signal phase operator 574 performs an arctangent operation on the ratio of signal i to signal r to obtain the phase of the reference signal Ss.

[0333] With this configuration, the phase of the reference signal Ss can be obtained instantaneously without sampling. Therefore, in the quadrature signal generation unit 57 having such a phase setting unit 579, the phase of the reference signal Ss can be reflected in the quadrature signal in real time.

[0334] 2. Second Implementation Method

[0335] Next, the laser interferometer according to the second embodiment will be described.

[0336] Figure 16 This is a functional block diagram illustrating the laser interferometer 1a according to the second embodiment. Figure 17 It is a detailed representation Figure 16The diagram shows the arithmetic unit 52 and the signal generation unit 61a in the functional block diagram.

[0337] The second embodiment will be described below, but the description will focus on the differences from the embodiment described above, omitting descriptions of identical items. Furthermore, in Figure 16 and Figure 17 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0338] This embodiment is the same as the first embodiment except that the configuration of the signal generation unit 61a and the correction processing unit 62a is different.

[0339] like Figure 16 As shown, the signal generation unit 61a includes a numerically controlled oscillator 616, a DAC 615, and an amplifier 614.

[0340] like Figure 17 As shown, the correction processing unit 62a includes multipliers 661 and 662, a sixth low-pass filter 663, a seventh low-pass filter 664, an amplitude and phase calculation unit 665, a frequency setting unit 627, and an amplitude and gain setting unit 626.

[0341] 2.1. Signal generation department

[0342] like Figure 16 As shown, the signal generation unit 61a includes a numerically controlled oscillator 616, a DAC 615, and an amplifier 614.

[0343] The numerically controlled oscillator 616 generates a periodic signal such as a sine wave or cosine wave by reading address data that is added at regular clock intervals from a ROM table containing the value of one cycle of a sine wave or cosine wave. Thus, the numerically controlled oscillator 616 generates a reference signal Ss with high precision as the target frequency and outputs it to the DAC 615. The DAC 615 is a digital-to-analog converter that generates an analog reference signal Ss based on the input digital reference signal Ss.

[0344] Amplifier 614 amplifies the input reference signal Ss to generate a drive signal Sd with the target amplitude, and outputs it to optical modulator 12.

[0345] The numerically controlled oscillator 616 includes an accumulator adder 651, an absolute value arithmetic unit 577, a third low-pass filter 578, a phase setting unit 579, an adder 652, a first period signal generator 653, and a second period signal generator 654.

[0346] The accumulator adder 651 accumulates and adds the frequency control signal Sf2 output from the frequency setting unit 627 of the correction processing unit 62a. The frequency control signal Sf2 is a phase lead amount per unit time step corresponding to the frequency to be set as the reference signal Ss, which will be described later. In the accumulator adder 651, this phase lead amount is accumulated and added together to calculate the accumulated sum value. The obtained accumulated sum value is output to the first cycle signal generator 653.

[0347] The first-cycle signal generator 653 includes a ROM (Read Only Memory) containing values ​​of one cycle of sine and cosine waves. The first-cycle signal generator 653 reads the value at the address corresponding to the accumulated sum. This generates a sine wave signal and a cosine wave signal with a frequency corresponding to the frequency control signal Sf2. The cosine wave signal, as a reference signal Ss, is output to the DAC 615 of the signal generation unit 61a and the multiplier 661 of the correction processing unit 62a, respectively. The sine wave signal, as a reference signal Ss', is output to the multiplier 662 of the correction processing unit 62a.

[0348] In the phase setting unit 579, as described above, the phase quantity 'a' to be added to the accumulated sum in the adder 652 is set. In the adder 652, the sum of the accumulated sum and the phase quantity 'a' is calculated. The resulting sum of the accumulated sum and the phase quantity 'a' is output to the second cycle signal generator 654.

[0349] The second-cycle signal generator 654 includes a ROM (Read Only Memory) containing values ​​of one cycle of sine and cosine waves. In the second-cycle signal generator 654, the value at the address corresponding to the sum of the accumulated sum and the phase quantity a is read. Thus, a sine wave signal sin(θ) with a phase shift of phase quantity a can be generated at a frequency corresponding to the frequency control signal Sf2. m (t) and cosine wave signal cos(θ) m (t)). Cosine wave signal cos(θ) m (t) is output to the multiplier 538 and the demodulation processing unit 55 (described later), and a sine wave signal sin(θ) is generated. m (t)) Outputs toward the demodulation processing unit 55.

[0350] The above describes an example of the configuration of the numerically controlled oscillator 616, but the configuration of the numerically controlled oscillator 616 is not limited to the above.

[0351] 2.2. Calibration Processing Department

[0352] like Figure 16As shown, the output signal Sm, which is output in accordance with the drive of the optical modulator 12, is input to the correction processing unit 62a. In the correction processing unit 62a, the phase difference between the output signal Sm and the reference signal Ss, as well as the amplitude of the output signal Sm, are obtained by quadrature detection.

[0353] In addition, the correction processing unit 62a has the function of outputting a frequency control signal Sf2 (correction signal) to the numerical control oscillator 616 and an amplification control signal Sam (correction signal) to the amplifier 614.

[0354] The output signal Sm from the optical modulator 12 is transmitted via Figure 16 The ADC543 shown is input to the correction processing unit 62a. The ADC543 is an analog-to-digital converter. The output signal Sm, which is converted into a digital signal in the ADC543, is as follows: Figure 17 The signal is divided into two parts. The output signal Sm of one part is multiplied by the reference signal Ss in multiplier 661. The signal output from multiplier 661 passes through the sixth low-pass filter 663 and is input as signal I to amplitude-phase calculation unit 665. The output signal Sm of the other part is multiplied by the reference signal Ss' in multiplier 662. The signal output from multiplier 662 passes through the seventh low-pass filter 664 and is input as signal Q to amplitude-phase calculation unit 665.

[0355] The transmission bandwidth of the sixth low-pass filter 663 and the seventh low-pass filter 664 is preferably a bandwidth above the frequency at which the driving signal Sd can be removed.

[0356] The amplitude-phase calculation unit 665 performs an atan(Q / I) calculation to calculate the phase of the output signal Sm. The amplitude-phase calculation unit 665 outputs the phase difference between the output signal Sm and the reference signal Ss to the frequency setting unit 627. Additionally, the amplitude-phase calculation unit 665 performs (I... 2 +Q 2 ) 1 / 2 The amplitude and phase calculation unit 665 calculates the amplitude of the output signal Sm. The amplitude and phase calculation unit 665 outputs the calculated amplitude to the amplitude gain setting unit 626. The amplitude and phase calculation unit 665 may use a CORDIC (Coordinate Rotation Digital Computer) as a hardware demodulation circuit, but is not limited to this.

[0357] The frequency setting unit 627 has the function of determining the target frequency of the reference signal Ss. Furthermore, the frequency setting unit 627 controls the frequency control signal Sf2 to make the frequency of the reference signal Ss the target frequency, and outputs the frequency control signal Sf2 to the numerical control oscillator 616.

[0358] In the numerically controlled oscillator 616, a reference signal Ss is generated based on the frequency control signal Sf2. Thus, the frequency of the reference signal Ss is corrected.

[0359] The amplitude gain setting unit 626 has the function of determining the target amplitude of the drive signal Sd. Furthermore, the amplitude gain setting unit 626 controls the amplification control signal Sam to make the amplitude of the drive signal Sd the target amplitude, and outputs the amplification control signal Sam to the amplifier 614.

[0360] In amplifier 614, the amplitude of the drive signal Sd is amplified according to the amplification control signal Sam. As a result, the amplitude of the drive signal Sd is corrected.

[0361] 2.3. Effects of the second implementation method

[0362] As described above, the laser interferometer 1a according to this embodiment includes a laser source 2, an optical modulator 12, a light-receiving element 10, a calculation unit 52, and a signal generation unit 61a. The laser source 2 emits outgoing light L1 (laser). The optical modulator 12 includes a vibrating element 30 driven by a drive signal Sd, and the vibrating element 30 is used to overlap the modulation signal with the outgoing light L1. The light-receiving element 10 receives object light L3 (laser containing a sampled signal) and reference light L2 (laser containing a modulation signal), which are superimposed by reflection from an object 14, and outputs a received light signal. The calculation unit 52 performs calculations on the received light signal based on a reference signal Ss. The signal generation unit 61a outputs the drive signal Sd and the reference signal Ss.

[0363] Furthermore, the arithmetic unit 52 includes a preprocessing unit 53, a demodulation unit 55, and a correction unit 62a. The preprocessing unit 53 performs preprocessing to extract frequency modulation components from the received light signal, outputting a preprocessed signal S(t) containing the frequency modulation components. The demodulation unit 55 mixes the preprocessed signal S(t) with orthogonal signals to obtain signals x and y (mixed signals), and then demodulates the sampled signal from signals x and y. The correction unit 62a outputs an amplification control signal Sam and a frequency control signal Sf1 as correction signals based on the output signal Sm output corresponding to the drive of the vibrating element 30. Moreover, the signal generation unit 61 corrects the drive signal Sd and the reference signal Ss based on the amplification control signal Sam and the frequency control signal Sf2.

[0364] In this configuration, even under external interference such as temperature changes, the frequency or amplitude of the drive signal Sd can follow the changes in the mechanical resonant frequency or vibration amplitude of the vibrating element 30. Therefore, the frequency and amplitude of the vibration of the vibrating element 30 can be kept constant. As a result, the decrease in the S / N ratio of the modulation signal can be suppressed, and the decrease in the demodulation accuracy of the sampled signal can be suppressed. Thus, a laser interferometer 1a can be realized that can measure the displacement or velocity of the object 14 with high accuracy even under external interference. Furthermore, by using the signal generation unit 61a and the correction processing unit 62a, the vibrating element 30 can be driven near its mechanical resonant frequency, thus reducing the power consumption of the laser interferometer 1a.

[0365] Furthermore, in this embodiment, the correction processing unit 62a acquires the phase difference between the output signal Sm and the reference signal Ss, as well as the amplitude of the output signal Sm, through quadrature detection. Based on quadrature detection, the phase difference and amplitude can be acquired instantaneously. Therefore, correction processing can be performed in real time.

[0366] Furthermore, in this embodiment, a numerically controlled oscillator 616 is used as the oscillator in the signal generation unit 61. According to the numerically controlled oscillator 616, a periodic signal can be generated based on the value read from the ROM table. Therefore, the numerically controlled oscillator 616 is not affected by noise, etc., and can output high-precision reference signals Ss, Ss', and a high-precision cosine wave signal cos(θ). m (t) and the sinusoidal signal sin(θ) m (t)). This improves the accuracy of preprocessing or demodulation in the computation unit 52, and also improves the demodulation accuracy of the sampled signal. As a result, a laser interferometer 1a can be realized that can measure the displacement or velocity of the object 14 with higher precision.

[0367] 3. Examples of variations of optical systems

[0368] Next, the first to fourth modifications of the optical system 50 will be described.

[0369] Figure 18 This is a schematic diagram showing the configuration of the optical system 50A involved in the first modified example. Figure 19 This is a schematic diagram showing the configuration of the optical system 50B involved in the second variation. Figure 20 This is a schematic diagram showing the configuration of the optical system 50C involved in the third variation. Figure 21 This is a schematic diagram showing the configuration of the optical system 50D involved in the fourth variation.

[0370] The first to fourth modifications of the optical system 50 will be described below, but the description will focus on the differences from the aforementioned optical system 50, omitting descriptions of identical items. Furthermore, in Figures 18 to 21 In the middle, to and Figure 2 The same items are labeled with the same reference numerals. Additionally, in Figures 18 to 21 The illustrations of some optical elements have been omitted.

[0371] Figure 18 The optical system 50A shown is different from the light incident on the light-receiving element 10, the light modulator 12, and the object 14, except that the light is different. Figure 2 The optical system 50 shown is the same. Specifically, in Figure 18 In the optical system 50A shown, the emitted light L1 is incident on the light-receiving element 10 and the light modulator 12. Figure 18 In the optical modulator 12 shown, the emitted light L1 is modulated to generate a reference light L2 containing a modulation signal. This reference light L2 is then incident on the object 14. Furthermore, the object light L3, containing a sampling signal, generated by the reflection of the reference light L2 on the object 14, is incident on the light-receiving element 10. Therefore, Figure 18 The light-receiving element 10 shown receives object light L3 (laser light containing sampling and modulation signals) and emitted light L1, which includes sampling and modulation signals.

[0372] Figure 19 The optical system 50B shown differs from the optical system 50B in that, except for the arrangement of the light-receiving element 10, the light modulator 12, and the object 14, it is similar in function to the optical system 50B shown to the optical system 50B. Figure 18 The optical system shown is the same as that of the 50A.

[0373] That is, the optical systems 50A and 50B involved in the first and second modifications include a laser source 2, an optical modulator 12, and a light-receiving element 10. The laser source 2 emits outgoing light L1. The optical modulator 12 uses a vibrating element to modulate the outgoing light L1, generating a reference light L2 containing a modulation signal. The light-receiving element 10 receives the object light L3 (a laser beam containing a sampling signal and a modulation signal) generated by the reflection of the reference light L2 on the object 14, as well as the outgoing light L1, and outputs a received light signal.

[0374] Figure 20 The optical system 50C shown differs from the optical system 50C in that, except for the different configurations of the light modulator 12 and the object 14, and the different light incident on the light-receiving element 10, the light modulator 12, and the object 14, it is otherwise identical. Figure 18 The optical system shown is the same as 50A. Specifically, in Figure 20In the optical system 50C shown, emitted light L1 is incident on the light-receiving element 10 and the object 14. The emitted light L1 is reflected by the object 14 to generate object light L3. This object light L3 is then incident on the light modulator 12. Furthermore, in... Figure 20 In the optical modulator 12 shown, the object light L3 is modulated to generate a reference light L2 containing a sampling signal and a modulation signal. This reference light L2 is incident on the light-receiving element 10. Therefore, Figure 20 The light-receiving element 10 shown receives a reference light L2 (a laser beam containing a sampling signal and a modulation signal) and an outgoing light L1, both of which contain a sampling signal and a modulation signal.

[0375] Figure 21 The optical system 50D shown differs from the optical system 50D in that, except for the configuration of the light-receiving element 10, the light modulator 12, and the object 14, it is similar in function to the optical system 50D shown in the image. Figure 20 The optical system shown is the same as that of 50C.

[0376] That is, the laser interferometers equipped with the optical systems 50C and 50D according to the third and fourth modifications include a laser source 2, an optical modulator 12, and a light-receiving element 10. The laser source 2 emits outgoing light L1. The optical modulator 12 has a vibrating element and uses the vibrating element to modulate the object light L3 to generate a reference light L2 containing a modulation signal. The vibrating element has a vibration component in a direction that intersects the incident plane of the object light L3 containing a sampling signal generated by the reflection of the outgoing light L1 at the object 14. The light-receiving element 10 receives the object light L2 (laser containing the sampling signal and the modulation signal) and the outgoing light L1, and outputs a received light signal.

[0377] The optical systems 50A, 50B, 50C, and 50D described above also have the same functions as the aforementioned optical system 50.

[0378] The laser interferometer of the present invention has been described above with reference to the illustrated embodiments. However, the laser interferometer of the present invention is not limited to the embodiments described above, and the configuration of each part can be replaced with any configuration having the same function. Furthermore, other arbitrary components can be added to the laser interferometer involved in the embodiments. Moreover, the laser interferometer of the present invention may also include two of the embodiments described above. Additionally, the functional units of the laser interferometer of the present invention can be divided into multiple elements, or multiple functional units can be combined into one.

[0379] In addition to the aforementioned displacement gauges and velocities, the laser interferometer of the present invention can also be applied to vibratory meters, inclinometers, rangefinders (length measuring devices), etc. Furthermore, as applications of the laser interferometer of the present invention, examples include optical comb interferometry technology capable of measuring distance, 3D imaging, and beam splitting, as well as fiber optic gyroscopes such as angular velocity sensors and angular acceleration sensors.

[0380] Furthermore, two or more of the laser source, optical modulator, and light-receiving element can be mounted on the same substrate. This facilitates the miniaturization and weight reduction of the optical system and improves assembly ease.

[0381] Furthermore, while the various embodiments described herein have a so-called Michelson-type interferometric optical system, the laser interferometer of the present invention can also be applied to laser interferometers with other types of interferometric optical systems, such as Mach-Zehnder-type interferometric optical systems.

Claims

1. A laser interferometer, characterized in that, have: Laser source, emits laser light; An optical modulator includes a vibrating element driven by a driving signal, wherein the laser incident on the optical modulator is subjected to a frequency shift of a first frequency by the vibrating element and thus contains a modulation signal; A light-receiving element receives the laser light incident on an object, which is subjected to a Doppler frequency shift at a second frequency and contains a sampling signal, as well as the laser light containing the modulation signal, and outputs a light-receiving signal; The arithmetic unit performs calculations on the received light signal based on the reference signal; and The signal generation unit outputs the drive signal and the reference signal. The arithmetic unit has: The preprocessing unit performs preprocessing to extract frequency modulation components from the received light signal based on the reference signal, and outputs a preprocessed signal containing the frequency modulation components. The demodulation processing unit demodulates the sampled signal from the preprocessed signal based on the reference signal; as well as The correction processing unit outputs a correction signal based on the output signal corresponding to the drive of the vibration element. The signal generation unit corrects the drive signal and the reference signal based on the correction signal.

2. The laser interferometer according to claim 1, characterized in that, The correction processing unit corrects the frequency of the reference signal and the frequency of the drive signal based on the phase difference between the output signal and the reference signal.

3. The laser interferometer according to claim 2, characterized in that, The correction processing unit corrects the amplitude of the drive signal based on the amplitude of the output signal.

4. The laser interferometer according to claim 3, characterized in that, The correction processing unit obtains the phase difference between the output signal and the reference signal, as well as the amplitude of the output signal, through orthogonal detection.

5. The laser interferometer according to any one of claims 1 to 4, characterized in that, The signal generation unit has: An oscillator generates the reference signal; and An amplifier adjusts the amplitude of the reference signal and outputs it as the drive signal.

6. The laser interferometer according to claim 5, characterized in that, The oscillator is a voltage-controlled oscillator that generates the reference signal through voltage control.

7. The laser interferometer according to claim 5, characterized in that, The oscillator is a numerically controlled oscillator that generates the reference signal through numerical control.

8. The laser interferometer according to claim 1, characterized in that, The vibrating element is a quartz oscillator.

Images