laser interferometer

Abstract

To provide a laser interferometer that can improve the accuracy of demodulating a received light signal to obtain a sample signal derived from an object to be measured even when a signal whose phase changes, such as a signal output from an oscillation circuit, is used as a reference signal.SOLUTION: A laser interferometer includes: a laser light source that emits a first laser beam; an optical modulator that has an oscillating element and generates a second laser beam containing a modulation signal; a light receiving element that receives a third laser beam containing a sample signal and the second laser beam; and a calculation part that obtains a displacement of an object to be measured from a received light signal based on a reference signal. The calculation part includes: a preprocessing unit that performs preprocessing to extract a frequency modulation component from the received light signal and outputs a preprocessed signal; a demodulation processor that performs demodulation processing to extract the sample signal from a mixed signal after obtaining the mixed signal by mixing the preprocessed signal with a quadrature signal; and a quadrature signal generator that generates the quadrature signal based on the phase of the reference signal and the amplitude of the preprocessed signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laser interferometer. [Background technology]

[0002] Patent Document 1 discloses an optical Doppler velocimeter that measures the velocity of an object to be measured by utilizing the Doppler effect that occurs in a light beam reflected from the object to be measured when a light beam is irradiated onto the object from a light source.

[0003] Specifically, in the optical Doppler velocimeter described in Patent Document 1, a light source light beam emitted from a light source is first irradiated onto an object to be measured to obtain a measurement light beam, and the light source light beam is then modulated by an optical modulator to obtain a reference light beam. A phase modulation signal is supplied to the optical modulator. The optical modulator phase-modulates the light source light beam using this phase modulation signal.

[0004] Next, a photodetector detects the combined light beam containing the measurement light beam and the reference light beam, obtaining a photodetection signal with a frequency-modulated component corresponding to the phase-modulated signal. The resulting photodetection signal is then AM-demodulated using two pilot signals, and then FM-demodulated. This allows the velocity of the object under test to be determined.

[0005] In this type of optical Doppler velocimeter, a phase-modulated signal and two pilot signals are synchronized with the sine wave signal output from a crystal oscillator. This allows the phase of the phase-modulated signal to be aligned with the optical detection signal obtained from the optical detector. As a result, the distortion components contained in the demodulated signal after FM demodulation can be kept small, enabling highly accurate velocity measurements. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 07-151772 Summary of the Invention [Problem to be solved by the invention]

[0007] The optical Doppler velocimeter described in Patent Document 1 uses a quartz oscillator as a reference signal generator. The quartz oscillator includes a quartz crystal resonator and a circuit for driving the quartz crystal resonator. Examples of circuits for driving a quartz crystal oscillator include an oscillator circuit including an inverter. Such oscillator circuits have the advantage of being relatively simple and therefore easily miniaturized. However, when an oscillator circuit is used, the phase of the voltage signal extracted from the oscillator circuit is affected by factors such as the capacitance of the capacitor included in the oscillator circuit and the parasitic capacitance of the circuit. Because the capacitance of the capacitor and the parasitic capacitance of the circuit change depending on the environment, such as the ambient temperature, the phase of the voltage signal extracted from the oscillator circuit also changes. This in turn changes the phase of the sinusoidal signal that serves as the reference for synchronizing the aforementioned phase-modulated signal and two pilot signals. As a result, it becomes difficult to accurately align the phase of the optical detection signal with the phase-modulated signal, resulting in a problem of reduced accuracy in measuring the velocity of the object being measured. [Means for solving the problem]

[0008] A laser interferometer according to an application example of the present invention includes: a laser light source that emits a first laser beam; an optical modulator including a vibration element, the optical modulator modulating the first laser light using the vibration element to generate a second laser light including a modulation signal; a light-receiving element that receives the second laser light and a third laser light including a sample signal generated by reflection of the first laser light from a measurement object, and outputs a light-receiving signal; a calculation unit that calculates the displacement of the object to be measured from the light receiving signal based on a reference signal; Equipped with The calculation unit a pre-processing unit that performs pre-processing to extract a frequency modulation component from the received light signal and outputs a pre-processed signal; a demodulation processing unit that mixes the pre-processed signal with an orthogonal signal to obtain a mixed signal, and then performs a demodulation process to extract the sample signal from the mixed signal; a quadrature signal generating unit that generates the quadrature signal based on the phase of the reference signal and the amplitude of the pre-processed signal, or the phase of the reference signal and the amplitude of the mixed signal; The present invention is characterized by having the following. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a functional block diagram showing a laser interferometer according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the sensor head unit shown in FIG. [Figure 3] FIG. 3 is a perspective view showing a first configuration example of the optical modulator shown in FIG. [Figure 4] FIG. 10 is a plan view showing a part of a second configuration example of the optical modulator. [Figure 5] FIG. 10 is a plan view showing a third configuration example of the optical modulator. [Figure 6] 1 is a conceptual diagram illustrating the generation of multiple diffracted beams when incident light Ki is incident on the surface of a vibration element in a direction perpendicular to the surface. [Figure 7] FIG. 10 is a conceptual diagram illustrating an optical modulator configured so that the angle formed between the traveling direction of incident light Ki and the traveling direction of reference light L2 is 180°. [Figure 8] FIG. 10 is a conceptual diagram illustrating an optical modulator configured so that the angle formed between the traveling direction of incident light Ki and the traveling direction of reference light L2 is 180°. [Figure 9] FIG. 10 is a conceptual diagram illustrating an optical modulator configured so that the angle formed between the traveling direction of incident light Ki and the traveling direction of reference light L2 is 180°. [Figure 10] FIG. 1 is a cross-sectional view showing an optical modulator having a package structure. [Figure 11] FIG. 1 is a circuit diagram showing the configuration of a single-stage inverter oscillator circuit. [Figure 12] 1 is an example of an LCR equivalent circuit of a vibration element. [Figure 13]4 is a flowchart showing an example of a method by which a phase amount setting unit shown in FIG. 1 sets a phase amount. [Figure 14] 14 shows examples of waveforms indicating the preprocessed signal S(t) before the calibration of the laser interferometer based on the flow shown in FIG. 13, the phase information demodulated by the demodulation processing unit (phase information before unwrapping), and the phase information subjected to phase unwrapping processing by the signal output unit (phase information after unwrapping). [Figure 15] 14 shows examples of waveforms indicating the preprocessed signal S(t) after the laser interferometer has been calibrated based on the flow shown in FIG. 13, the phase information demodulated by the demodulation processing unit (phase information before unwrapping), and the phase information subjected to phase unwrapping processing by the signal output unit (phase information after unwrapping). [Figure 16] FIG. 10 is a functional block diagram showing a laser interferometer according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laser interferometer according to the present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. 1. First embodiment First, the laser interferometer according to the first embodiment will be described. FIG. 1 is a functional block diagram showing a laser interferometer according to the first embodiment.

[0011] The laser interferometer 1 shown in FIG. 1 has an optical system 50, a sensor head unit 51 including a current-voltage converter 531 and an oscillation circuit 54, and a calculation unit 52 to which a light detection signal from the optical system 50 is input.

[0012] 1.1.Sensor head FIG. 2 is a schematic diagram showing the configuration of the sensor head unit 51 shown in FIG.

[0013] 1.1.1.Optical system As described above, the sensor head unit 51 includes the optical system 50 . As shown in FIG. 2, the optical system 50 includes a laser light source 2, a collimating lens 3, a light 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, a frequency shifter-type optical modulator 12, and a set section 16 in which an object to be measured 14 is placed.

[0014] The laser light source 2 emits emitted light L1 (first laser light). The light receiving element 10 converts the received light into an electrical signal. The optical modulator 12 includes a vibration element 30, which changes the frequency of the emitted light L1 to generate reference light L2 (second laser light) containing a modulated signal. The setting unit 16 may be provided as needed, and is configured to allow the measurement object 14 to be placed thereon. The emitted light L1 incident on the measurement object 14 is reflected as object light L3 (third laser light) containing a sample signal, which is a Doppler signal derived from the measurement object 14.

[0015] The optical path of the output light L1 emitted from the laser light source 2 is referred to as optical path 18. On optical path 18, a collimator lens 3 and a half-wave plate 6 are arranged in this order from the laser light source 2 side. Optical path 18 is coupled to optical path 20 by reflection at the optical splitter 4. On optical path 20, a quarter-wave plate 8 and an optical modulator 12 are arranged in this order from the optical splitter 4 side. Furthermore, optical path 18 is coupled to optical path 22 by transmission through the optical splitter 4. On optical path 22, a quarter-wave plate 7 and a setting unit 16 are arranged in this order from the optical splitter 4 side.

[0016] The optical path 20 is coupled to an optical path 24 by passing through the optical splitter 4. On the optical path 24, an analyzer 9 and a light receiving element 10 are arranged in this order from the optical splitter 4 side.

[0017] The output light L1 emitted from the laser light source 2 is split into two by the optical splitter 4, one of which travels along optical path 20 and enters the optical modulator 12. The other travels along optical path 22 and enters the measurement object 14. The reference light L2 generated by the optical modulator 12 travels along optical path 20 and optical path 24 and enters the light receiving element 10. The object light L3 generated by reflection from the measurement object 14 travels along optical path 22 and optical path 24 and enters the light receiving element 10. In this specification, the term "optical path" refers to a path along which light travels that is set between optical components.

[0018] Each part of the optical system 50 will be further described below. Laser light source The laser light source 2 is a laser light source that emits coherent output light L1. A light source with a linewidth in the MHz range or less is preferably used as the laser light source 2. Specific examples include gas lasers such as He-Ne lasers, and semiconductor laser elements such as DFB-LDs (Distributed Feedback Laser Diodes), FBG-LDs (Laser Diodes with Fiber Bragg Gratings), VCSELs (Vertical Cavity Surface Emitting Lasers), and FP-LDs (Fabry-Perot Laser Diodes).

[0019] It is particularly preferable that the laser light source 2 is a semiconductor laser element. This allows the laser light source 2 to be particularly compact, which in turn allows the laser interferometer 1 to be made smaller. In particular, the sensor head 51 of the laser interferometer 1, which houses the optical system 50, can be made smaller and lighter, which is also useful in terms of improving the operability of the laser interferometer 1.

[0020] 1.1.1.2.Collimating lens The collimating lens 3 is a convex lens disposed between the laser light source 2 and the light splitter 4. The collimating lens 3 collimates the outgoing light L1 emitted from the laser light source 2.

[0021] If the light L1 emitted from the laser light source 2 is sufficiently collimated, for example, if a gas laser such as a He—Ne laser is used as the laser light source 2, the collimator lens 3 may be omitted.

[0022] On the other hand, when the laser light source 2 is a semiconductor laser element, the laser interferometer 1 preferably includes a collimating lens 3 disposed between the laser light source 2 and the beam splitter 4. This allows the emitted light L1 emitted from the semiconductor laser element to be collimated. As a result, the emitted light L1 becomes collimated light, which prevents the various optical components that receive the emitted light L1 from becoming larger, and allows the laser interferometer 1 to be made more compact.

[0023] The collimated output light L1 passes through the half-wave plate 6, where it is converted into linearly polarized light with an intensity ratio of P-polarized light to S-polarized light of, for example, 50:50, and enters the light splitter 4.

[0024] 1.1.1.3.Light splitter The light splitter 4 is a polarizing beam splitter that is placed between the laser light source 2 and the optical modulator 12, and between the laser light source 2 and the measurement object 14. The light splitter 4 has the function of transmitting P-polarized light and reflecting S-polarized light. With this function, the light splitter 4 splits the output light L1 into a first divided light L1a that is a reflected light at the light splitter 4, and a second divided light L1b that is transmitted through the light splitter 4.

[0025] The first divided 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 enters the optical modulator 12. The circularly polarized light of the first divided light L1a that enters the optical modulator 12 is expressed as f m [Hz] and is reflected as reference light L2. Therefore, the reference light L2 has a frequency f mThe reference light L2 is converted to P-polarized light when it passes through the quarter-wave plate 8 again. The P-polarized light of the reference light L2 passes through the optical splitter 4 and the analyzer 9 and enters the light-receiving element 10.

[0026] The second divided 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 is incident on the moving object 14. The circularly polarized light of the second divided light L1b that has entered the object 14 is expressed as f d The object light L3 is Doppler shifted by a frequency of f d The object light L3 is converted to S-polarized light when it passes through the quarter-wave plate 7 again. The S-polarized light of the object light L3 is reflected by the optical splitter 4, passes through the analyzer 9, and enters the light-receiving element 10.

[0027] As described above, the output light L1 has coherence, so the reference light L2 and the object light L3 enter the light receiving element 10 as interference light.

[0028] Note that a non-polarizing beam splitter may be used instead of the polarizing beam splitter. In this case, the half-wave plate 6, the quarter-wave plate 7, the quarter-wave plate 8, etc. are not required, which reduces the number of parts and allows for the miniaturization of the laser interferometer 1. Also, a light splitter other than a beam splitter may be used.

[0029] Analyzer Since the S-polarized light and the P-polarized light are orthogonal to each other and independent of each other, simply superimposing them does not produce beat noise due to interference. Therefore, the light waves of the superimposed S-polarized light and P-polarized light are passed through an analyzer 9 tilted at 45 degrees to both the S-polarized light and the P-polarized light. By using the analyzer 9, light with common components can be transmitted, causing interference. As a result, the reference light L2 and the object light L3 interfere with each other in the analyzer 9, and |f m -f d Interference light with a frequency of |[Hz] is generated.

[0030] 1.1.1.5.Photodetector When the interference light is incident on the light receiving element 10, the light receiving element 10 outputs a light receiving signal. By demodulating this light receiving signal into a sample signal using a method described below, it is possible to ultimately determine the movement of the measurement object 14, i.e., the vibration velocity and displacement. The light receiving element 10 may be, for example, a photodiode. The light receiving element 10 receives the interference light and outputs a photocurrent.

[0031] Optical Modulator FIG. 3 is a perspective view showing a first configuration example of the optical modulator 12 shown in FIG.

[0032] 1.1.1.6.1. Overview of the first example of optical modulator configuration The frequency shifter type optical modulator 12 has an optical modulation oscillator 120. The optical modulation oscillator 120 shown in FIG.

[0033] The vibration element 30 is made of a material that, when an electric potential is applied, repeats a vibration mode in which the vibration is distorted in a direction along the surface. In this configuration example, the vibration element 30 is a quartz crystal AT resonator that vibrates in a thickness-shear mode along a vibration direction 36 in a high frequency region in the MHz band. A diffraction grating 34 is formed on the surface of the vibration element 30. The diffraction grating 34 has grooves 32 that have components that intersect with the vibration direction 36, i.e., a plurality of linear grooves 32 that extend in a direction that intersects with the vibration direction 36.

[0034] The substrate 31 has a front surface 311 and a back surface 312 which are opposite surfaces. The vibration elements 30 are arranged on the front surface 311. The front surface 311 is also provided with pads 33 for applying a potential to the vibration elements 30. Meanwhile, the back surface 312 is also provided with pads 35 for applying a potential to the vibration elements 30.

[0035] The size of the substrate 31 is, for example, about 0.5 mm or more and 10.0 mm or less in terms of the long side. The thickness of the substrate 31 is, for example, about 0.10 mm or more and 2.0 mm or less. As an example, the shape of the substrate 31 is a square with each side measuring 1.6 mm, and the thickness is 0.35 mm.

[0036] The size of the vibration element 30 is, for example, about 0.2 mm or more and 3.0 mm or less in terms of the long side, and the thickness of the vibration element 30 is, for example, about 0.003 mm or more and 0.5 mm or less.

[0037] As an example, the shape of the vibrating element 30 is a square with sides 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. Note that by changing the thickness of the vibrating element 30 and taking into account overtones, the oscillation frequency can be adjusted within a range from 1 MHz to 1 GHz.

[0038] In FIG. 3, the diffraction grating 34 is formed on the entire surface of the vibration element 30, but it may be formed on only a part of the surface.

[0039] The magnitude of the optical modulation by the optical modulator 12 is given by the dot product of the differential wave vector between the wave vector of the output light L1 entering the optical modulator 12 and the wave vector of the reference light L2 exiting from the optical modulator 12, and the vector in the vibration direction 36 of the vibration element 30. In this configuration example, the vibration element 30 vibrates in a thickness-shear manner, but because this vibration is an in-plane vibration, optical modulation cannot be achieved even if light is incident perpendicularly to the surface of the vibration element 30 alone. Therefore, in this configuration example, a diffraction grating 34 is provided in the vibration element 30, making optical modulation possible based on a principle described below.

[0040] The diffraction grating 34 shown in Fig. 3 is a blazed diffraction grating. A blazed diffraction grating is a diffraction grating whose cross section has a stepped shape. The linear grooves 32 of the diffraction grating 34 are arranged so that their extension direction is perpendicular to the vibration direction 36.

[0041] 1 and 2 to the vibration element 30 shown in Fig. 3, the vibration element 30 oscillates. The electric power (driving power) required for oscillation of the vibration element 30 is not particularly limited, but is small, about 0.1 μW to 100 mW. Therefore, the drive signal Sd output from the oscillation circuit 54 can be used to oscillate the vibration element 30 without amplifying it.

[0042] Furthermore, conventional optical modulators sometimes require a structure to maintain the temperature of the optical modulator, making it difficult to reduce their volume. Furthermore, conventional optical modulators have a problem in that they consume a lot of power, making it difficult to reduce the size and power consumption of the laser interferometer. In contrast, in this configuration example, the volume of the vibration element 30 is very small and the power required for oscillation is also small, making it easy to reduce the size and power consumption of the laser interferometer 1.

[0043] 1.1.1.6.2. Method of forming a diffraction grating The method for forming the diffraction grating 34 is not particularly limited. One example is to create a mold using a mechanical ruling engine, and then form the grooves 32 on an electrode formed on the surface of the vibration element 30 of the quartz crystal AT resonator using a nanoimprinting method. The reason for forming the grooves on the electrode is that, in principle, a quartz crystal AT resonator can generate high-quality thickness-shear vibration on the electrode. The grooves 32 do not necessarily have to be formed on the electrode, but may also be formed on the surface of a material in the non-electrode portion. Alternatively, instead of nanoimprinting, other processing methods such as exposure and etching, electron beam lithography, and focused ion beam (FIB) processing may be used.

[0044] Alternatively, a diffraction grating may be formed on the chip of a quartz crystal AT resonator using a resist material, and a metal film or a dielectric multilayer mirror film may be provided on top of the grating. By providing a metal film or a mirror film, the reflectance of the diffraction grating 34 can be increased.

[0045] Furthermore, a resist film may be formed on a chip or wafer of a quartz crystal AT resonator, processed by etching, and then removed. A metal film or mirror film may then be formed on the processed surface. In this case, the resist material is removed, eliminating the effects of moisture absorption by the resist material and improving the chemical stability of the diffraction grating 34. Furthermore, by providing a highly conductive metal film such as Au or Al, it can also be used as an electrode for driving the resonator element 30.

[0046] The diffraction grating 34 may be formed using techniques such as anodic alumina (porous alumina).

[0047] 1.1.1.6.3.Other Configuration Examples of Optical Modulators The vibrating element 30 is not limited to a quartz vibrator, but may be, for example, a Si vibrator, a surface acoustic wave (SAW) device, a ceramic vibrator, or the like.

[0048] Fig. 4 is a plan view showing a part of a second configuration example of the optical modulator 12. Fig. 5 is a plan view showing a third configuration example of the optical modulator 12.

[0049] 4 is a Si vibrator manufactured from a Si substrate using MEMS technology. MEMS (Micro Electro Mechanical Systems) stands for micro-electromechanical systems.

[0050] The vibration element 30A includes a first electrode 301 and a second electrode 302 adjacent to each other on the same plane with a gap therebetween, a diffraction grating mounting portion 303 provided on the first electrode 301, and a diffraction grating 34 provided on the diffraction grating mounting portion 303. The first electrode 301 and the second electrode 302 vibrate, for example, by electrostatic attraction as a driving force, in the left-right direction in FIG. 4, i.e., along an axis connecting the first electrode 301 and the second electrode 302 shown in FIG. 4, so as to repeatedly approach and move away from each other. This allows in-plane vibration to be imparted to the diffraction grating 34. The oscillation frequency of the Si vibrator is, for example, from about 1 kHz to several hundred MHz.

[0051] The vibrating element 30B shown in Fig. 5 is a SAW device that uses surface waves. SAW (Surface Acoustic Wave) stands for surface acoustic wave.

[0052] The vibration element 30B includes a piezoelectric substrate 305, an interdigital electrode 306 provided on the piezoelectric substrate 305, a ground electrode 307, a diffraction grating mounting portion 303, and a diffraction grating 34. When an AC voltage is applied to the interdigital electrode 306, a surface acoustic wave is excited due to the inverse piezoelectric effect. This allows the diffraction grating 34 to vibrate in-plane. The oscillation frequency of the SAW device is, for example, from several hundred MHz to several GHz.

[0053] In the above-described device, by providing a diffraction grating 34, optical modulation becomes possible according to the principle described below, as in the case of a quartz crystal AT oscillator.

[0054] On the other hand, if the vibration element 30 is a quartz crystal oscillator, a highly accurate modulation signal can be generated by utilizing the extremely high Q value of the quartz crystal. The Q value is an index that indicates the sharpness of the resonance peak. Furthermore, a quartz crystal oscillator has the advantage of being less susceptible to external disturbances. Therefore, by using a modulation signal modulated by the optical modulator 12 equipped with a quartz crystal oscillator, a sample signal derived from the measurement object 14 can be acquired with high accuracy.

[0055] 1.1.1.6.4.Light modulation by vibration elements Next, the principle of modulating light using the vibration element 30 will be described.

[0056] FIG. 6 shows the incident light K i 1 is a conceptual diagram illustrating the generation of multiple diffracted beams when incident light.

[0057] Light K is incident on a diffraction grating 34 that is vibrating in thickness shear along a vibration direction 36. i When the incident light is incident on the surface, the diffraction phenomenon causes multiple diffracted light beams K ns is generated. n is the diffracted light Kns where n=0, ±1, ±2, .... The diffraction grating 34 shown in FIG. 6 is not the blazed diffraction grating shown in FIG. 3, but is a diffraction grating with repeated concaves and convexes as an example of another diffraction grating. Also, in FIG. 6, diffracted light K 0s is omitted from the illustration.

[0058] In Figure 6, the incident light K i is incident on the surface of the vibration element 30 from a direction perpendicular to the surface of the vibration element 30, but this incident angle is not particularly limited, and the incident angle may be set so that the light is incident obliquely on the surface of the vibration element 30. When the light is incident obliquely, the diffracted light K ns The direction of travel also changes accordingly.

[0059] Depending on the design of the diffraction grating 34, higher-order light of |n| ≥ 2 may not appear. Therefore, to obtain a stable modulated signal, it is desirable to set |n| = 1. That is, in the laser interferometer 1 of FIG. 2, the frequency shifter-type optical modulator 12 is preferably arranged so that the ±1st-order diffracted light is used as the reference light L2. This arrangement enables stable measurement by the laser interferometer 1.

[0060] On the other hand, when high-order light of |n|≧2 emerges from the diffraction grating 34, the optical modulator 12 may be arranged so that any of the ±2nd-order or higher-order diffracted light is used as the reference light L2, rather than the ±1st-order diffracted light. This allows the use of high-order diffracted light, thereby achieving higher frequency and miniaturization of the laser interferometer 1.

[0061] In this embodiment, as an example, incident light K i The optical modulator 12 is configured so that the angle formed between the direction of incidence of the reference beam L2 and the direction of travel of the reference beam L2 emitted from the optical modulator 12 is 180°. Three examples will be described below with reference to Figs. 7 to 9.

[0062] 7 to 9 show the incident light K i1 is a conceptual diagram illustrating an optical modulator 12 configured so that the angle formed between the traveling direction of the reference light L1 and the traveling direction of the reference light L2 is 180°.

[0063] The optical modulator 12 shown in FIG. 7 includes a mirror 37 in addition to the vibration element 30. The mirror 37 reflects the diffracted light K 1s The mirror 37 is arranged to reflect the diffracted light K 1s The angle between the incident angle of the diffracted light K and the reflection angle of the mirror 37 is 180°. 1s is diffracted again by the diffraction grating 34 and incident on the optical modulator 12. i Therefore, by adding the mirror 37, the incident light K i This satisfies the condition that the angle formed between the incident direction of the reference beam L1 and the traveling direction of the reference beam L2 is 180°.

[0064] Furthermore, by passing the reference light L2 through the mirror 37 in this way, the reference light L2 generated by the optical modulator 12 is subjected to frequency modulation twice. Therefore, by using the mirror 37 in combination, higher frequency modulation is possible compared to when the vibration element 30 is used alone.

[0065] In Fig. 8, the vibration element 30 is tilted relative to the arrangement in Fig. 6. The tilt angle θ S is the incident light K i The angle formed by the incident direction of the reference light L1 and the traveling direction of the reference light L2 is set to 180°.

[0066] The diffraction grating 34 shown in FIG. B The blazed diffraction grating has the following structure: incident light K propagating at an incident angle β with respect to the normal N of the surface of the vibration element 30. i is incident on the diffraction grating 34, the blaze angle θ B Therefore, the reference light L2 returns at the same angle as the incident angle β. BBy making it equal to the incident light K i 7 and 8, the condition that the angle between the direction of incidence of the reference beam L1 and the direction of travel of the reference beam L2 is 180° can be satisfied. In this case, the condition can be satisfied without using the mirror 37 shown in Fig. 7 or without tilting the vibration element 30 itself as shown in Fig. 8, which allows the laser interferometer 1 to be further miniaturized and operate at a higher frequency. In particular, in the case of a blazed diffraction grating, an arrangement that satisfies the condition is called a "Littrow arrangement," which has the advantage of being able to particularly increase the diffraction efficiency of the diffracted light.

[0067] 9 indicates the pitch of the blazed diffraction grating, and as an example, the pitch P is set to 1 μm. B is set to, for example, 25°. In this case, in order to satisfy the above condition, the incident light K i The angle of incidence β with respect to the normal N should also be set to 25°.

[0068] Package Structure FIG. 10 is a cross-sectional view showing an optical modulator 12 having a package structure.

[0069] 10 includes a container 70 serving as a housing, an optical modulation oscillator 120 housed in the container 70, and a circuit element 45 constituting an oscillation circuit 54. The container 70 is hermetically sealed in a reduced pressure atmosphere such as a vacuum, or in an inert gas atmosphere such as nitrogen or argon.

[0070] 10, the container 70 has a container body 72 and a lid 74. Of these, the container body 72 has a first recess 721 provided therein and a second recess 722 provided inside the first recess 721 and deeper than the first recess 721. The container body 72 is made of, for example, a ceramic material, a resin material, or the like. Although not shown, the container body 72 also has internal terminals provided on the inner surface, external terminals provided on the outer surface, wiring connecting the internal terminals and the external terminals, and the like.

[0071] The opening of the container body 72 is closed by a lid 74 via a sealing member such as a seal ring or low-melting-point glass (not shown). The lid 74 is made of a material that is transparent to laser light, such as a glass material.

[0072] The optical modulation oscillator 120 is disposed on the bottom surface of the first recess 721. The optical modulation oscillator 120 is supported on the bottom surface of the first recess 721 by a bonding member (not shown). Furthermore, the internal terminal of the container body 72 and the optical modulation oscillator 120 are electrically connected via a conductive material (not shown), such as a bonding wire or a bonding metal.

[0073] The circuit element 45 is disposed on the bottom surface of the second recess 722. The circuit element 45 is electrically connected to an internal terminal of the container body 72 via a bonding wire 76. As a result, the optical modulation oscillator 120 and the circuit element 45 are also electrically connected via the wiring provided in the container body 72. Note that the circuit element 45 may be provided with a circuit other than the oscillation circuit 54 described below.

[0074] By adopting such a package structure, the optical modulation oscillator 120 and the circuit element 45 can be stacked, thereby reducing the physical distance between them and shortening the wiring length between them. This makes it possible to prevent external noise from entering the drive signal Sd, or conversely, to prevent the drive signal Sd from becoming a noise source. Furthermore, a single container 70 can protect both the optical modulation oscillator 120 and the circuit element 45 from the external environment. This makes it possible to reduce the size of the sensor head unit 51 while improving the reliability of the laser interferometer 1.

[0075] The structure of the container 70 is not limited to the structure shown in the figure, and for example, the optical modulation oscillator 120 and the circuit element 45 may have separate package structures. Although not shown, the container 70 may also house other circuit elements that make up the oscillation circuit 54. The container 70 may be provided as needed, and may be omitted.

[0076] 1.1.2. Current-to-voltage converter The current-voltage converter 531 is also called a transimpedance amplifier (TIA), and converts the photocurrent (received light signal) output from the light receiving element 10 into a voltage signal, which is output as a light detection signal.

[0077] The optical system 50 may include a plurality of light receiving elements 10. In this case, by providing a differential amplifier circuit between the plurality of light receiving elements 10 and the current-voltage converter 531, it is possible to perform differential amplification processing on the photocurrent and increase the S / N ratio (signal-to-noise ratio) of the photodetection signal. The differential amplification processing may also be performed on the voltage signal.

[0078] 1 is disposed between the current-voltage converter 531 and the calculation unit 52. The ADC 532 is an analog-to-digital converter, and converts an analog signal into a digital signal with a predetermined number of sampling bits.

[0079] Oscillator Circuit 1, the oscillation circuit 54 outputs a drive signal Sd that is input to the optical modulator 12 of the optical system 50. The oscillation circuit 54 also outputs a reference signal Ss that is input to the calculation unit 52.

[0080] The oscillator circuit 54 is not particularly limited, and circuits of various configurations can be used as long as they are capable of oscillating the vibration element 30. As an example of the circuit configuration, a circuit diagram showing the configuration of a single-stage inverter oscillator circuit is shown in FIG.

[0081] The oscillation circuit 54 shown in FIG. 11 includes a circuit element 45, a feedback resistor Rf, a limiting resistor Rd, a first capacitor Cg, a second capacitor Cd, and a third capacitor C3.

[0082] The circuit element 45 is an inverter IC. The terminals X1 and X2 of the circuit element 45 are terminals connected to the inverters inside the circuit element 45. The terminal GND is connected to the ground potential, and the terminal Vcc is connected to the power supply potential. The terminal Y is a terminal for oscillation output.

[0083] A first capacitor Cg is connected between terminal X1 and ground potential. A limiting resistor Rd and a second capacitor Cd are connected in series between terminal X2 and ground potential, in that order from the terminal X2 side. Furthermore, one end of a feedback resistor Rf is connected between terminal X1 and the first capacitor Cg, and the other end of the feedback resistor Rf is connected between terminal X2 and limiting resistor Rd.

[0084] One end of the vibration element 30 is connected between the first capacitor Cg and the feedback resistor Rf, and the other end of the vibration element 30 is connected between the second capacitor Cd and the limiting resistor Rd. This makes the vibration element 30 a signal source for the oscillation circuit 54.

[0085] FIG. 12 is an example of an LCR equivalent circuit of the vibration element 30. As shown in FIG. 12, the LCR equivalent circuit of the vibrating element 30 is made up of a series capacitance C1, a series inductance L1, an equivalent series resistance R1, and a parallel capacitance C0.

[0086] In the oscillation circuit 54 shown in FIG. 11, the capacitance of the first capacitor Cg is set to C g The capacitance of the second capacitor Cd is C d Then, the load capacitance C L is given by the following equation (a):

[0087]

number

[0088] Then, the oscillation frequency f output from the terminal Y of the oscillation circuit 54 is osc is given by the following equation (b):

[0089]

number

[0090] f Q is the natural frequency of the vibration element 30. According to the above formula (b), the load capacitance C L By appropriately changing the oscillation frequency f of the signal output from terminal Y, osc It can be seen that the

[0091] In addition, the natural frequency f of the vibration element 30 Q and the oscillation frequency f of the oscillator circuit 54 osc The difference Δf between and is given by the following equation (c):

[0092]

number

[0093] where C1< <C0、C1<<C L Therefore, Δf is approximately given by the following equation (d):

[0094]

number

[0095] Therefore, the oscillation frequency f of the oscillator circuit 54 osc is the natural frequency f of the vibration element 30 Q The value depends on the

[0096] Here, when the vibration element 30 is fixed to, for example, the container 70, if it is subjected to expansion stress due to temperature via the fixing part, the natural frequency f Q Furthermore, when the vibration element 30 is tilted, the natural frequency f Q fluctuates.

[0097] For this reason, the oscillator circuit 54 has a natural frequency fQ Even if fluctuates, the oscillation frequency f osc In other words, the oscillation frequency f osc is always increased by Δf, and the natural frequency f Q This stabilizes the vibration of the vibration element 30 and the displacement amplitude. The stable displacement amplitude stabilizes the modulation characteristics of the optical modulator 12, thereby improving the demodulation accuracy of the sample signal in the calculation unit 52.

[0098] As an example, Δf = |f osc -f Q It is preferable that the frequency is |≦3000 [Hz], and more preferably 600 [Hz].

[0099] As described above, in the laser interferometer 1 according to this embodiment, the optical modulator 12 includes the vibration element 30, and the optical modulator 12 uses the vibration element 30 to modulate the first divided light L1a.

[0100] With this configuration, it is possible to reduce the size and weight of the optical modulator 12, and therefore the size and weight of the laser interferometer 1 can be reduced.

[0101] The laser interferometer 1 also includes a calculation unit 52 and an oscillation circuit 54. The oscillation circuit 54 uses the vibration element 30 as its signal source, and outputs a reference signal Ss to the calculation unit 52, as shown in Fig. 1. The calculation unit 52 demodulates a sample signal derived from the measurement object 14 from the light detection signal based on the reference signal Ss.

[0102] With this configuration, the natural frequency f Q Even if the oscillation frequency f of the oscillator circuit 54 fluctuates, osc The natural frequency f of the vibration element 30 QSince the temperature characteristic of the modulation signal can be changed to a value according to the temperature, it is possible to easily stabilize the vibration of the vibration element 30. This allows the temperature characteristic of the modulation signal to correspond to the temperature characteristic of the vibration element 30, and it is possible to stabilize the modulation characteristic of the optical modulator 12. As a result, it is possible to improve the demodulation accuracy of the sample signal in the calculation unit 52.

[0103] Furthermore, in the above configuration, the temperature characteristics of the reference signal Ss output from the oscillator circuit 54 to the calculation unit 52 can also be made to correspond to the temperature characteristics of the vibration element 30. In this way, both the temperature characteristics of the modulated signal and the temperature characteristics of the reference signal correspond to the temperature characteristics of the vibration element 30, so that the behavior of the fluctuations in the modulated signal and the behavior of the fluctuations in the reference signal Ss that accompany temperature changes match or are similar to each other. Therefore, even if the temperature of the vibration element 30 changes, the effect on demodulation accuracy can be suppressed, and the demodulation accuracy of the sample signal derived from the measurement object 14 can be improved.

[0104] Furthermore, since the power consumption of the oscillator circuit 54 is low, the power consumption of the laser interferometer 1 can be easily reduced.

[0105] As mentioned above, the vibrating element 30 is preferably a quartz crystal vibrator. This allows for the generation of a highly accurate modulated signal by utilizing the extremely high Q value of quartz crystal. As a result, the sample signal derived from the measurement object 14 can be acquired with high accuracy.

[0106] Instead of the oscillation circuit 54, a signal generator such as a function generator or a signal generator may be used.

[0107] 1.2. Arithmetic section The calculation unit 52 performs a demodulation process to demodulate the light detection signal output from the current-voltage converter 531 into a sample signal derived from the measurement object 14. The sample signal includes, for example, phase information and frequency information. The displacement of the measurement object 14 can be obtained from the phase information, and the velocity of the measurement object 14 can be obtained from the frequency information. If different physical quantities can be obtained in this way, the laser interferometer 1 can be given the functions of a displacement meter and a speed meter, thereby improving the functionality of the laser interferometer 1.

[0108] The circuit configuration of the calculation unit 52 is set according to the modulation processing method. The laser interferometer 1 according to this embodiment uses an optical modulator 12 equipped with a vibration element 30. The vibration element 30 is an element that vibrates simply, and therefore the vibration speed changes from moment to moment within the period. For this reason, the modulation frequency also changes over time, and a conventional demodulation circuit cannot be used as is.

[0109] A conventional demodulation circuit refers to a circuit that demodulates a sample signal from an optical detection signal that includes a modulated signal modulated using, for example, an acousto-optic modulator (AOM). An acousto-optic modulator does not change its modulation frequency. Therefore, while a conventional demodulation circuit can demodulate a sample signal from an optical detection signal that includes a modulated signal whose modulation frequency does not change, it cannot directly demodulate a sample signal that includes a modulated signal modulated by an optical modulator 12 whose modulation frequency changes.

[0110] Therefore, the calculation unit 52 shown in FIG. 1 has a preprocessing unit 53, a demodulation processing unit 55, and a quadrature signal generation unit 57. The photodetection signal output from the current-voltage converter 531 first passes through the preprocessing unit 53 and is then guided to the demodulation processing unit 55. The preprocessing unit 53 performs preprocessing on the photodetection signal. This preprocessing extracts a frequency modulation component from the received light signal, thereby obtaining a signal that can be demodulated by a conventional demodulation circuit. Therefore, the demodulation processing unit 55 demodulates the sample signal derived from the measurement object 14 using a known demodulation method. Furthermore, the quadrature signal generation unit 57 generates a cosine wave signal cos(θ), which is a quadrature signal, based on the reference signal Ss output from the oscillation circuit 54 and the preprocessed signal S(t) output from the preprocessing unit 53. m (t)) and the sinusoidal signal sin(θ m (t)).

[0111] The above-described functions of the calculation unit 52 are realized by hardware including, for example, a processor, a memory, an external interface, an input unit, a display unit, etc. These components are capable of communicating with each other via an internal bus.

[0112] Examples of processors include a field-programmable gate array (FPGA), a central processing unit (CPU), and a digital signal processor (DSP).

[0113] Examples of memory 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).

[0114] Examples of the external interface include a digital input / output port such as a USB (Universal Serial Bus), an Ethernet (registered trademark) port, and the like.

[0115] Examples of the input unit include various input devices such as a keyboard, a mouse, a touch panel, a touch pad, etc. Examples of the display unit include a liquid crystal display panel, an organic EL (Electro Luminescence) display panel, etc.

[0116] 1.2.1. Configuration of the preprocessing unit 1 includes a first band-pass filter 534, a second band-pass filter 535, a first delay adjuster 536, a multiplier 538, a third band-pass filter 539, a first AGC unit 540, a second AGC unit 541, and an adder 542. Note that AGC stands for Auto Gain Control.

[0117] The photodetection signal output from the current-voltage converter 531 is split into two signals, a first signal S1 and a second signal S2, at the branch point jp1. In Fig. 1, the path of the first signal S1 is referred to as a first signal path ps1, and the path of the second signal S2 is referred to as a second signal path ps2.

[0118] First band-pass filter 534, second band-pass filter 535, and third band-pass filter 539 are filters that selectively transmit signals in specific frequency bands.

[0119] 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 two input signals. The adder 542 is a circuit that generates an output signal proportional to the sum of the two input signals.

[0120] Next, the operation of the pre-processing unit 53 will be described along the flow of the first signal S1 and the second signal S2.

[0121] The first signal S1 passes through a first band-pass filter 534 arranged on the first signal path ps1, and then the group delay is adjusted by a first delay adjuster 536. The group delay adjusted by the first delay adjuster 536 corresponds to the group delay of the second signal S2 caused by a second band-pass filter 535, which will be described later. This delay adjustment makes it possible to align the delay times associated with passing through the filter circuits between the first band-pass filter 534, through which the first signal S1 passes, and the second band-pass filter 535 and third band-pass filter 539, through which the second signal S2 passes. The first signal S1 that has passed through the first delay adjuster 536 passes through a first AGC unit 540 and is input to an adder 542.

[0122] The second signal S2 is passed through a second band-pass filter 535 arranged on the second signal path ps2, and then input to a multiplier 538. The multiplier 538 multiplies the second signal S2 by a cosine wave signal cos(θ m Then, the second signal S2 is passed through a third band-pass filter 539, and then passed through a second AGC unit 541 and input to an adder 542. The adder 542 outputs a signal proportional to the sum of the first signal S1 and the second signal S2.

[0123] Preprocessing Next, the pre-processing in the pre-processing unit 53 will be described. In the following description, as an example, a system will be considered in which the frequency of the modulation signal changes sinusoidally and the displacement of the measurement object 14 also changes in simple harmonic motion in the optical axis direction. Here, E m , E d , φ,

[0124]

number

[0125] When this is the case, the light detection signal I output from the current-voltage converter 531 is PD is theoretically expressed by the following equation:

[0126]

number

[0127] In addition, E m , E d , φ m , φ d , φ, ω m , ω d ,ω0,a m , a d are as follows:

[0128]

number

[0129] In addition, < > in equation (4) represents the time average. The first and second terms in the above equation (4) represent the DC component, and the third term represents the AC component. This AC component is called I PD·AC Then, I PD·AC is expressed as follows:

[0130]

number

[0131] Here, the v-order Bessel functions such as the following formulas (8) and (9) are known.

[0132]

number

[0133] When the above formula (5) is expanded into a series using the Bessel functions of the above formulas (8) and (9), it can be transformed into the following formula (10).

[0134]

number

[0135] where J0(B), J1(B), J2(B), ... are Bessel coefficients.

[0136] By modifying it as described above, it can be said that, theoretically, it is possible to extract a band corresponding to a specific order using a band-pass filter. Based on this theory, the pre-processing unit 53 pre-processes the AC component of the photodetection signal in the following manner.

[0137] First, the amplitude of the AC component of the photodetection signal output from the current-voltage converter 531 is normalized by the ADC 532. The signal after passing through the ADC 532 is expressed by the following equation (10-1).

[0138]

number

[0139] After passing through the ADC 532, the signal is split into a first signal S1 and a second signal S2 at a branching point jp1. The first signal S1 is passed through a first band-pass filter 534. The first band-pass filter 534 has a center angular frequency of ω m As a result, the first signal S1 after passing through the first band-pass filter 534 is expressed by the following equation.

[0140]

number

[0141] On the other hand, the second signal S2 is passed through a second band-pass filter 535. The center angular frequency of the second band-pass filter 535 is set to a value different from the center angular frequency of the first band-pass filter 534. Here, as an example, the center angular frequency of the second band-pass filter 535 is set to 2ω m As a result, the second signal S2 after passing through the second band-pass filter 535 is expressed by the following equation.

[0142]

number

[0143] The second signal S2 after passing through the second band-pass filter 535 is multiplied by a multiplier 538 using a cosine wave signal cos(θ m The second signal S2 after passing through the multiplier 538 is expressed by the following equation.

[0144]

number

[0145] In the above equation (13), α is the amount of phase deviation of the reference signal Ss from its original phase. The original phase is the phase when the pre-processed signal S(t) output from the pre-processing unit 53 is a signal that is only frequency-modulated or a signal equivalent thereto.

[0146] The second signal S2 after passing through the multiplier 538 is passed through a third band-pass filter 539. The central angular frequency of the third band-pass filter 539 is set to the same value as the central angular frequency of the first band-pass filter 534. Here, as an example, the central angular frequency of the third band-pass filter 539 is set to ω m As a result, the second signal S2 after passing through the third band-pass filter 539 is expressed by the following equation.

[0147]

number

[0148] Thereafter, the first signal S1 expressed by the above equation (11) is adjusted in phase by the first delay adjuster 536 and in amplitude by the first AGC unit 540.

[0149] The amplitude of the second signal S2 expressed by the above equation (14) is also adjusted by the second AGC unit 541, so that the amplitude of the second signal S2 is made equal to the amplitude of the first signal S1. The first signal S1 after the amplitude adjustment is expressed by the following equation (14-1), and the second signal S2 after the amplitude adjustment is expressed by the following equation (14-2).

[0150]

number

[0151] The first signal S1 and the second signal S2 are then added together by an adder 542. The addition result is defined as a preprocessed signal S(t). The preprocessed signal S(t) is expressed by the following equation (15).

[0152]

number

[0153] As in the above equation (15), the preprocessed signal S(t) is expressed by an equation including a phase shift width α. Therefore, when the phase shift width α is an integer multiple of π, the above equation (15) can be expressed by the following equation (15-1).

[0154]

number

[0155] In this specification, when the preprocessed signal S(t) is expressed by the above formula (15-1), it is said to be "in phase." On the other hand, when the preprocessed signal S(t) is expressed by the above formula (15) and the phase shift amount α is other than an integer multiple of π, it is said to be "out of phase."

[0156] When the phases are aligned, the preprocessed signal S(t) is expressed by the above equation (15-1), and can be said to be a signal that is only frequency modulated. In such a preprocessed signal S(t), the frequency modulated component is extracted, and therefore the demodulation accuracy of the sample signal in the demodulation processing unit 55 can be improved. On the other hand, when the phases are not aligned, the preprocessed signal S(t) can be said to be a signal in which frequency modulation and amplitude modulation are superimposed. With such a preprocessed signal S(t), it is difficult to improve the demodulation accuracy of the sample signal in the demodulation processing unit 55.

[0157] 1.2.3. Configuration of the quadrature signal generator The orthogonal signal generation unit 57 shown in Figure 1 has a fourth bandpass filter 571, a Hilbert transform filter 572, a second delay adjuster 573 (reference signal delay unit), a reference signal phase calculator 574, an absolute value calculator 577, a third lowpass filter 578, a phase amount setting unit 579, an adder 580, a cosine calculator 581, and a sine calculator 582.

[0158] In this embodiment, the orthogonal signal generator 57 generates a cosine wave signal cos(θ m (t)) and the sinusoidal signal sin(θ m In this specification, the process of generating such an orthogonal waveform is referred to as "orthogonal waveform generation process."

[0159] An ADC 533 is connected between the oscillator circuit 54 and the fourth band-pass filter 571. The ADC 533 is an analog-to-digital converter that converts an analog signal into a digital signal at a predetermined sampling bit rate. The fourth band-pass filter 571 is a filter that selectively passes signals in a specific frequency band.

[0160] The Hilbert transform filter 572 performs Hilbert transform processing on the reference signal Ss to obtain a signal i. The reference signal Ss output from the oscillation circuit 54 is expressed as cos(ω m ω mis the angular frequency of the modulated signal by the optical modulator 12, and t is time. The Hilbert transform process shifts the phase of this reference signal Ss by π / 2.

[0161] The second delay adjuster 573 is a circuit that adjusts the delay of the signal using a memory that temporarily stores the signal, and introduces a delay in the reference signal Ss that is equivalent to the delay introduced by the Hilbert transform process, thereby obtaining the signal r.

[0162] The reference signal phase calculator 574 calculates the phase of the reference signal Ss from 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, i.e., atan(i / r), on the ratio of signal i / signal r.

[0163] Absolute value calculator 577 calculates the absolute value of preprocessed signal S(t) output from preprocessing unit 53. Third low-pass filter 578 is a filter that cuts signals in the high frequency band with respect to the absolute value of preprocessed signal S(t) output from absolute value calculator 577.

[0164] The phase amount setting unit 579 has the function of acquiring the envelope of the signal output from the third low-pass filter 578, the function of acquiring the maximum and minimum values ​​of the envelope (amplitude of the envelope), and the function of outputting the phase amount a.

[0165] The adder 580 outputs a signal proportional to the sum of the output from the reference signal phase calculator 574 and the output from the phase amount setting unit 579. The cosine calculator 581 calculates a cosine wave signal cos(θ m The sine calculator 582 generates a sine wave signal sin(θ m (t)).

[0166] 1.2.4. Quadrature waveform generation process In the orthogonal waveform generation process, first, the reference signal Ss output from the ADC 533 is input to the fourth band-pass filter 571. The fourth band-pass filter 571 has a center angular frequency of ω m The reference signal Ss output from the fourth band-pass filter 571 is split into two, one of which is input to a Hilbert transform filter 572 and the other of which is input to a second delay adjuster 573.

[0167] The Hilbert transform filter 572 shifts the phase of the reference signal Ss by π / 2 to generate a signal i. The second delay adjuster 573 delays the reference signal Ss to generate a signal r. The signals i and r are input to the reference signal phase calculator 574.

[0168] The reference signal phase calculator 574 calculates atan(i / r) to obtain the phase of the reference signal Ss. The calculation result atan(i / r) is input to the adder 580.

[0169] Meanwhile, absolute value calculator 577 obtains the absolute value of preprocessed signal S(t). This converts the negative waveform of preprocessed signal S(t) to the positive waveform and synthesizes the signal. The signal from absolute value calculator 577 is input to third low-pass filter 578.

[0170] Third low-pass filter 578 cuts off signals in the high frequency band. This allows phase amount setting unit 579 to easily and accurately obtain an envelope. The signal from third low-pass filter 578 is input to phase amount setting unit 579.

[0171] Based on the signal from the third low-pass filter 578, the phase amount setting unit 579 sets the phase amount a to be added to the calculation result atan(i / r) in the adder 580. In other words, the orthogonal signal generating unit 57 adjusts the phase of the reference signal Ss. The setting method will be described later.

[0172] The adder 580 calculates the sum of the output from the reference signal phase calculator 574 and the output from the phase amount setting unit 579. Here, the sum is assumed to be β. β is a+a tan(i / r). Then, the cosine calculator 581 calculates the cosine wave signal cos(θ m (t)), and the sine calculator 582 generates a sine wave signal sin(θ m (t)) to generate a cosine wave signal cos(θ m (t)) is input to a multiplier 538 and a demodulation processing unit 55 (to be described later), and a sine wave signal sin(θ m (t)) is input to the demodulation processing unit 55. m (t) is ω m It is t-β.

[0173] 1.2.5. Phase amount setting method When the phases are not aligned, the phase amount setting unit 579 sets the phase amount a to be added by the adder 580 so that the influence of the amplitude modulation described above is minimized. As a result, the cosine calculator 581 and the sine calculator 582 calculate the cosine wave signal cos(θ m (t)) and the sinusoidal signal sin(θ m (t)) is generated. Then, this cosine wave signal cos(θ m The cosine wave signal cos(θ(t)) is reflected in the pre-processed signal S(t) via the multiplier 538, and the influence of amplitude modulation in the pre-processed signal S(t) is reduced. Finally, the phases can be aligned. Furthermore, when the phases are aligned, 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, demodulation processing from the preprocessed signal S(t) can be performed with high accuracy.

[0174] FIG. 13 is a flowchart showing an example of a method by which the phase amount setting unit 579 shown in FIG. 1 sets a phase amount. The phase amount setting shown in FIG. 13 is preferably performed using a standard sample vibrating at a single frequency as the measurement object 14. This allows the phase amount setting unit 579 to more accurately determine the phase amount a to be added in the adder 580. In the phase amount setting method shown in FIG. 13, the value of the phase amount a is changed little by little while repeatedly evaluating the amplitude of the preprocessed signal S(t). Then, the phase amount a when the amplitude is equal to or less than a predetermined value is stored in memory as an optimal value. Then, after the optimal phase amount a is determined, fixing the phase amount a enables highly accurate measurements of various measurement objects 14.

[0175] 13 is performed using the standard sample described above, for example, before measuring the measurement object 14 with the laser interferometer 1. This makes it possible to automatically calibrate the laser interferometer 1. Examples of the standard sample include a piezoelectric element and a quartz oscillator.

[0176] 13, first, the sign function sgn and the phase amount a are initialized. Specifically, a value of 1 is input to the sign function sgn, and a value of a0 is input to the phase amount a. The value a0 is an arbitrary value.

[0177] In step S104, the envelope of the preprocessed signal S(t) is obtained via absolute value calculator 577 and third low-pass filter 578. Methods for obtaining the envelope include, for example, a method using a low-pass filter or a method using a Hilbert transform. Then, 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).

[0178] In step S106, the phase amount setting unit 579 updates the phase amount a using the formula a+sgn*Δa → a and sets it as the output value. This formula means that a minute amount Δa is added to or subtracted from the current value of the phase amount a based on the two values ​​that the sign function sgn can take, i.e., 1 or -1, to obtain a new phase amount a. There are no particular restrictions on the minute amount Δa, as long as it is smaller than the phase amount a. The updated phase amount a is output to the adder 580. Then, the orthogonal signal generating unit 57 adjusts the phase of the reference signal Ss based on the new phase amount a set by the phase amount setting unit 579, and generates two orthogonal signals, i.e., the cosine wave signal cos(θ m (t)) and the sinusoidal signal sin(θ m Then, the pre-processing unit 53 generates a cosine wave signal cos(θ m (t)), a new preprocessed signal S(t) is generated.

[0179] In 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 in the same manner as in step S104. In step S108, this difference is designated as dS1.

[0180] In step S110, it is determined whether the difference dS1 is equal to or less than 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 a signal that is only frequency modulated. Therefore, if the difference dS1 is equal to or less than the predetermined value, it can be determined that the current phase amount a is optimal. Therefore, this flow ends. On the other hand, if the difference dS1 is greater than the predetermined value, it can be determined that the current phase amount a is not optimal, and the process proceeds to step S112.

[0181] In step S112, the number of times the determination in step S110 has been performed is obtained. Then, it is determined whether the obtained number of times is equal to or greater than a predetermined number. The predetermined number is, for example, the actual number of repetitions at which the optimal phase amount a can be obtained when repeatedly evaluating the amplitude of the preprocessed signal S(t) while gradually changing the value of the phase amount a, as described above, and in particular, the maximum value of the actual values ​​can be used. A specific example of the number of repetitions is the number of times the phase amount a is updated.

[0182] If the number of acquisitions is equal to or greater than the predetermined number, it can be determined that it is difficult to obtain the optimum phase amount a, and the process proceeds to step S114. In step S114, the phase amount setting unit 579 issues an error. In this case, the aforementioned display unit may display a message indicating that an error has occurred, prompting the user to take action, such as changing the standard sample. After issuing the error, the flow ends. On the other hand, if the number of times acquired is less than the predetermined number of times, the process proceeds to step S116.

[0183] In step S116, it is determined whether difference dS0 > difference dS1. If this is true, it can be determined that the influence of amplitude modulation has been reduced in the new pre-processed signal S(t). It can also be determined that the value of the sign function sgn initialized in step S102 was 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 amount a is updated again using the equation a + sgn * Δa → a. Since the sign function sgn in this equation has been determined to be appropriate, it is left unchanged. Then, the pre-processing unit 53 generates a new pre-processed signal S(t) that reflects the updated phase amount a.

[0184] 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, the influence of amplitude modulation is further reduced for the new preprocessed signal S(t), and it approaches a signal that is only frequency modulated.

[0185] On the other hand, if the difference dS0 > the difference dS1 is not satisfied in step S116, that is, if the difference dS0 ≦ the difference dS1, it can be determined that the new pre-processed signal S(t) has not been reduced in the influence of amplitude modulation. Also, it can be determined that the value of the sign function sgn initialized in step S102 was inappropriate. In this case, the process proceeds to step S120.

[0186] In step S120, the sign function sgn is inverted from the current value. That is, the current value is multiplied by -1 and the resulting value is input to the new sign function sgn. Then, the process proceeds to step S118.

[0187] 13, unless an error is issued, the phase amount a, the pre-processed signal S(t), and the difference dS0 are repeatedly updated until the difference dS1 becomes equal to or less than a predetermined value. As a result, the phase amount a is adjusted in the phase amount setting unit 579 until the pre-processed signal S(t) can be regarded as a signal that is only frequency-modulated, and the cosine wave signal cos(θ m (t)) and the sinusoidal signal sin(θ m (t)) will be generated.

[0188] The cosine wave signal cos(θ m By inputting the phase a(t)) into the preprocessing unit 53, the preprocessed signal S(t) can be brought closer to the original phase. As a result, the laser interferometer 1 can be calibrated. After the calibration, the measured object 14 can be measured using the obtained optimal phase amount a. This improves the accuracy of demodulating the sample signal from the light detection signal, enabling the measured object 14 to be measured with high precision. The laser interferometer 1 may be calibrated at any timing and frequency.

[0189] 1.2.6. Demodulation Processing Unit Configuration The demodulation processing unit 55 performs demodulation processing to demodulate the preprocessed signal S(t) into a sample signal derived from the measurement object 14. The demodulation processing is not particularly limited, but may be a well-known quadrature detection method. The quadrature detection method is a method of performing demodulation processing by externally mixing mutually orthogonal signals with respect to the input signal.

[0190] The demodulation processing unit 55 shown in FIG. 1 is a digital circuit including 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, an arctangent calculator 558, and a signal output unit 559.

[0191] Multipliers 551 and 552 are circuits that generate an output signal proportional to the product of two input signals. Inverting amplifier 553 has a gain of -1 and generates an output signal by inverting the phase of the input signal without changing the amplitude. First low-pass filter 555 and second low-pass filter 556 are filters that cut signals in high frequency bands.

[0192] The divider 557 is a circuit that generates an output signal proportional to the quotient of two input signals. The arctangent calculator 558 is a circuit that outputs the arctangent of the input signal. The signal output unit 559 calculates the phase φ as information derived from the object 14 to be measured from the phase φ acquired by the arctangent calculator 558. d Furthermore, the signal output unit 559 performs phase unwrapping when there is a phase jump of 2π between two adjacent points by phase unwrapping. Then, the displacement of the object 14 to be measured is calculated from the obtained phase information. This realizes a displacement meter. Furthermore, the velocity of the object 14 to be measured can be obtained from the displacement. This realizes a speed meter.

[0193] The demodulation processing unit 55 is not limited to a digital circuit, but may be an analog circuit, which may include an F / V converter circuit and a ΔΣ counter circuit.

[0194] Furthermore, the demodulation processing unit 55 may be configured to calculate frequency information derived from the measurement object 14. Based on the frequency information, the velocity of the measurement object 14 can be calculated.

[0195] 1.2.7. Demodulation process In the demodulation process, first, the pre-processed signal S(t) is split into two by the branching unit jp2. One of the split signals is multiplied by the multiplier 551 to obtain the sine wave signal sin(θ m (t)) via an inverting amplifier 553. That is, the multiplier 551 multiplies the pre-processed signal S(t) by a sine wave signal sin(θ m (t)) m The other signal after division is mixed with the cosine wave signal cos(θ m That is, the multiplier 552 multiplies the pre-processed signal S(t) by the cosine wave signal cos(θ m (t)) are mixed.

[0196] The signal that has passed through multiplier 551 passes through first low-pass filter 555 and is then input as signal y to divider 557. The signal that has passed through multiplier 552 passes through second low-pass filter 556 and is then input as signal x to divider 557. In this specification, signals x and y are collectively referred to as the "mixed signal." Divider 557 divides signal y by signal x, and passes the output y / x through arctangent calculator 558 to obtain the calculation result atan(y / x). This allows phase information of the sample signal to be obtained.

[0197] Thereafter, the calculation result atan(y / x) is input to the signal output unit 559, whereby the displacement and velocity of the measurement object 14 are output.

[0198] FIG. 14 shows an example of waveforms showing the preprocessed signal S(t) before the calibration of the laser interferometer 1 based on the flow shown in FIG. 13, the phase information demodulated by the demodulation processing unit 55 (phase information before unwrapping), and the phase information subjected to phase unwrapping processing by the signal output unit 559 (phase information after unwrapping).

[0199] As shown in Figure 14, the waveform of the preprocessed signal S(t) before calibration varies greatly in amplitude, resulting in a signal in which frequency modulation and amplitude modulation are superimposed. Therefore, the amplitude of the envelope of the preprocessed signal S(t) also increases. Therefore, the phase information before unwrapping shown in Figure 14 has an irregular waveform at the location indicated by the arrow, and the waveform of the phase information after unwrapping is discontinuous. In this case, it is difficult to accurately determine the displacement of the measurement object 14 from the phase information after unwrapping.

[0200] FIG. 15 shows an example of waveforms showing the preprocessed signal S(t) after the laser interferometer 1 has been calibrated based on the flow shown in FIG. 13, the phase information demodulated by the demodulation processing unit 55 (phase information before unwrapping), and the phase information subjected to phase unwrapping processing by the signal output unit 559 (phase information after unwrapping).

[0201] As shown in FIG. 15, the waveform of the preprocessed signal S(t) after calibration has little change in amplitude and is a signal that is almost entirely frequency modulated. Therefore, the amplitude of the envelope of the preprocessed signal S(t) also becomes small. Therefore, the phase information before unwrapping shown in FIG. 15 does not have an irregular waveform. Furthermore, the waveform of the phase information after unwrapping shown in FIG. 15 is a continuous waveform. In this case, the displacement of the measurement object 14 can be accurately determined from the phase information after unwrapping.

[0202] 1.2.8. Effects of the First Embodiment As described above, the laser interferometer 1 according to this embodiment includes a laser light source 2, an optical modulator 12, a light-receiving element 10, and a calculation unit 52. The laser light source 2 emits an output light L1 (first laser light). The optical modulator 12 includes a vibration element 30, and modulates the output light L1 using the vibration element 30 to generate a reference light L2 (second laser light) including a modulation signal. The light-receiving element 10 receives the reference light L2 and an object light L3 (third laser light) including a sample signal generated when the output light L1 is reflected by the measurement object 14, and outputs a light-receiving signal. The calculation unit 52 calculates the displacement of the measurement object 14 from the light-receiving signal based on the reference signal Ss. The calculation unit 52 also has a preprocessing unit 53, a demodulation processing unit 55, and an orthogonal signal generation unit 57. The preprocessing unit 53 performs preprocessing to extract frequency-modulated components from the received light signal and outputs a preprocessed signal S(t). The demodulation processing unit 55 mixes an orthogonal signal with the preprocessed signal S(t) to obtain signals x and y (mixed signals), and then performs demodulation processing to extract sample signals from the signals x and y. In this embodiment, the orthogonal signal generation unit 57 generates the above-mentioned orthogonal signal based on the phase of the reference signal Ss and the amplitude of the preprocessed signal S(t).

[0203] In this configuration, the orthogonal signal generator 57 adjusts the phase of the reference signal Ss based on the amplitude of the pre-processed signal S(t). Then, the adjusted cosine wave signal cos(θ m By inputting the reference signal Ss(t) to the preprocessing circuit 53, the preprocessed signal S(t) can be made closer to a signal that is frequency-modulated only, thereby improving the accuracy of demodulating the sample signal derived from the measurement object 14 from the received light signal. In other words, the laser interferometer 1 can be calibrated to enable highly accurate demodulation processing. As a result, even when the reference signal Ss output from the oscillation circuit 54 is used, a laser interferometer 1 can be realized that is capable of measuring the displacement and velocity of the measurement object 14 with high accuracy. This makes it easy to reduce the size, weight, and cost of the laser interferometer 1.

[0204] The orthogonal signal generating unit 57 also has a phase amount setting unit 579 that sets the phase of the orthogonal signal from the amplitude of the preprocessed signal S(t).

[0205] As described above, the phase amount setting unit 579 has a function of setting the phase amount a to be added by the adder 580. Then, the orthogonal signal generating unit 57 adjusts the phase of the reference signal Ss based on the phase amount a, and generates the orthogonal signal, that is, the cosine wave signal cos(θ m (t)) and the sinusoidal signal sin(θ m This orthogonal signal is mixed with the pre-processed signal S(t) in the demodulation processing unit 55. By appropriately setting the phase amount a, the phases of the pre-processed signal S(t) and the orthogonal signal can be aligned. As a result, the demodulation processing unit 55 can perform demodulation processing from the pre-processed signal S(t) with high accuracy.

[0206] The phase amount setting unit 579 sets the phase of the quadrature signal so that the difference between the maximum amplitude value of the preprocessed signal S(t) and the minimum amplitude value of the preprocessed signal S(t) is equal to or less than a predetermined value.

[0207] This allows the phase amount setting unit 579 to efficiently find an optimum phase amount a so that the preprocessed signal S(t) becomes a signal that is only frequency modulated or a signal equivalent thereto.

[0208] The orthogonal signal generation unit 57 has a Hilbert transform filter 572, a second delay adjuster 573 (reference signal delayer), and a reference signal phase calculator 574. The Hilbert transform filter 572 performs Hilbert transform processing on the reference signal Ss to obtain a signal i. The second delay adjuster 573 causes a delay in the reference signal Ss to obtain a signal r. The reference signal phase calculator 574 performs an arctangent calculation on the ratio of signal i / signal r to obtain the phase of the reference signal Ss.

[0209] With this configuration, the phase of the reference signal Ss can be obtained instantaneously without sampling the reference signal Ss. Therefore, the orthogonal signal generator 57 having this phase amount setting unit 579 can reflect the phase of the reference signal Ss in the orthogonal signal in a short time. As a result, the phase amount setting unit 579 can quickly find the optimal phase amount a.

[0210] 2. Second embodiment Next, a laser interferometer according to a second embodiment will be described. FIG. 16 is a functional block diagram showing a laser interferometer according to the second embodiment.

[0211] The second embodiment will be described below, focusing on the differences from the first embodiment and omitting a description of similarities. Note that in Fig. 16, the same reference numerals are used to designate the same components as those in the first embodiment.

[0212] In the first embodiment described above, the orthogonal signal generator 57 generates an orthogonal signal based on the phase of the reference signal Ss and the amplitude of the preprocessed signal S(t) obtained from the envelope of the preprocessed signal S(t). In contrast, in this embodiment, the orthogonal signal generator 57A generates an orthogonal signal based on the phase of the reference signal Ss and the amplitude of the signals x and y (mixed signal).

[0213] 2.1. Demodulation Processing Unit The demodulation processing unit 55A shown in FIG. 16 is the same as the demodulation processing unit 55 shown in FIG. 1, except that a mixed signal amplitude calculator 560 is added.

[0214] The mixed signal amplitude calculator 560 calculates the amplitude of two input signals, signal x and signal y, as follows: 2(x 2 +y 2 ) 1 / 2 and outputs the calculation result. This calculation result corresponds to the "amplitude of the mixed signal." In this specification, the signal output from mixed signal amplitude calculator 560 is referred to as the "amplitude signal Sa."

[0215] 2.2. Quadrature signal generator The orthogonal signal generation unit 57A shown in FIG. 16 is similar to the orthogonal signal generation unit 57 shown in FIG. 1, except that the absolute value calculator 577 and the third low-pass filter 578 are omitted, and the amplitude signal Sa output from the mixed signal amplitude calculator 560 is input to a phase amount setting unit 579A.

[0216] Phase amount setting unit 579A has a function of obtaining the maximum and minimum values ​​of amplitude signal Sa and a function of outputting phase amount a. Therefore, the phase amount setting method by phase amount setting unit 579A is the same as the method shown in Fig. 13 except that the "envelope of preprocessed signal S(t)" shown in Fig. 13 is replaced with the "amplitude signal Sa."

[0217] 2.3. Effects of the Second Embodiment Similar to the first embodiment, the laser interferometer 1A according to this embodiment includes a laser light source 2, an optical modulator 12, a light-receiving element 10, and a calculation unit 52. As shown in FIG. 16, the calculation unit 52 includes a preprocessing unit 53, a demodulation processing unit 55A, and a quadrature signal generation unit 57A. The preprocessing unit 53 performs preprocessing to extract a frequency-modulated component from the received light signal and outputs a preprocessed signal S(t). The demodulation processing unit 55A mixes a quadrature signal with the preprocessed signal S(t) to obtain signals x and y (mixed signals), and then performs demodulation processing to extract sample signals from the signals x and y. The quadrature signal generation unit 57A generates a quadrature signal based on the phase of the reference signal Ss and the amplitude of the signals x and y.

[0218] In this configuration, the orthogonal signal generating unit 57A adjusts the phase of the reference signal Ss based on the amplitude signal Sa. Then, the adjusted signal, that is, the cosine wave signal cos(θ m By inputting the reference signal Ss(t) to the preprocessing circuit 53, the preprocessed signal S(t) can be made closer to a signal that is frequency-modulated only, and the accuracy of demodulating the sample signal derived from the measurement object 14 from the received light signal can be improved. This makes it possible to calibrate the laser interferometer 1A. As a result, even when using the reference signal Ss output from the oscillation circuit 54, it is possible to realize a laser interferometer 1A that can measure the displacement and velocity of the measurement object 14 with high accuracy. This makes it easy to reduce the size, weight, and cost of the laser interferometer 1A.

[0219] The quadrature signal generating unit 57A also has a phase amount setting unit 579A that sets the phase of the quadrature signal from the amplitudes of the signals x and y (mixed signal).

[0220] Similar to the phase amount setting unit 579, the phase amount setting unit 579A has a function of setting the phase amount a to be added by the adder 580. Similarly to the orthogonal signal generating unit 57, the orthogonal signal generating unit 57A adjusts the phase of the reference signal Ss based on the phase amount a, and generates an orthogonal signal, that is, a cosine wave signal cos(θ m (t)) and the sinusoidal signal sin(θ m This orthogonal signal is mixed with the pre-processed signal S(t) in the demodulation processing unit 55. By appropriately setting the phase amount a, the phases of the pre-processed signal S(t) and the orthogonal signal can be aligned. As a result, the demodulation processing unit 55 can perform demodulation processing from the pre-processed signal S(t) with high accuracy.

[0221] The phase amount setting unit 579A sets the phase of the quadrature signal so that the difference between the maximum value of the amplitude of the signals x and y (mixed signal) and the minimum value of the amplitude of the signals x and y (mixed signal) is equal to or less than a predetermined value.

[0222] This allows the phase amount setting unit 579A to efficiently find the optimum phase amount a so that the preprocessed signal S(t) becomes a signal that is only frequency modulated or a signal equivalent thereto.

[0223] Moreover, the demodulation processing unit 55A shown in FIG. 16 has a mixed signal amplitude calculator 560 that obtains the amplitude of the signals x and y (mixed signal).

[0224] With this configuration, the amplitude of the preprocessed signal S(t) can be obtained without acquiring the envelope of the preprocessed signal S(t). That is, the absolute value calculator 577 and the third low-pass filter 578 in the first embodiment can be omitted. This simplifies the configuration of the orthogonal signal generator 57A. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0225] The laser interferometer of the present invention has been described above based on the illustrated embodiment, but the laser interferometer of the present invention is not limited to the embodiment, and the configuration of each part can be replaced with any configuration having a similar function. Furthermore, any other component may be added to the laser interferometer according to the embodiment. Furthermore, the laser interferometer of the present invention may be a combination of two of the above embodiments. Furthermore, each functional part of the laser interferometer of the present invention may be divided into multiple elements, or multiple functional parts may be integrated into one.

[0226] In addition to the displacement meters and speed meters described above, the laser interferometer of the present invention can also be applied to, for example, vibrometers, inclinometers, distance meters (length measuring devices), etc. Applications of the laser interferometer of the present invention include optical comb interferometry technology that enables distance measurement, 3D imaging, spectroscopy, etc., and optical fiber gyros that realize angular velocity sensors, angular acceleration sensors, etc.

[0227] Two or more of the laser light source, the optical modulator, and the light receiving element may be mounted on the same substrate, which facilitates miniaturization and weight reduction of the optical system and increases ease of assembly.

[0228] Furthermore, although each of the above-described embodiments has a so-called Michelson type interference optical system, the laser interferometer of the present invention can also be applied to an interferometer having other types of interference optical system, for example, a Mach-Zehnder type interference optical system. [Explanation of symbols]

[0229] 1...laser interferometer, 1A...laser interferometer, 2...laser light source, 3...collimating lens, 4...light splitter, 6...half wave plate, 7...quarter wave plate, 8...quarter wave plate, 9...analyzer, 10...light receiving element, 12...optical modulator, 14...measurement object, 16...setting unit, 18...optical path, 20...optical path, 22...optical path, 24...optical path, 30...vibration element, 30A...vibration element, 30B...vibration element, 31...substrate, 32...groove, 33...pad, 34...diffraction grating, 35...pad, 36...vibration direction, 37...mirror, 45...rotation Path element, 50...optical system, 51...sensor head unit, 52...arithmetic unit, 53...preprocessing unit, 54...oscillating circuit, 55...demodulation processing unit, 55A...demodulation processing unit, 57...orthogonal signal generating unit, 57A...orthogonal signal generating unit, 70...container, 72...container body, 74...lid, 76...bonding wire, 120...light 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 surface, 531...current-voltage conversion 532...ADC, 533...ADC, 534...first band-pass filter, 535...second band-pass filter, 536...first delay adjuster, 538...multiplier, 539...third band-pass filter, 540...first AGC unit, 541...second AGC unit, 542...adder, 551...multiplier, 552...multiplier, 553...inverting amplifier, 555...first low-pass filter, 556...second low-pass filter, 557...divider, 558...arctangent calculator, 559...signal output unit, 560...mixed signal amplitude Calculator, 571...fourth band pass filter, 572...Hilbert transform filter, 573...second delay adjuster, 574...reference signal phase calculator, 577...absolute value calculator, 578...third low pass filter, 579...phase amount setting unit, 579A...phase amount setting unit, 580...adder, 581...cosine calculator, 582...sine calculator, 721...first recess, 722...second recess, C0...parallel capacitance, C1...series capacitance, C3...third capacitor, Cd...second capacitor, Cg...first capacitor, cos(θ m (t))...Cosine wave signal, GND...GND terminal, K -2s ...diffracted light, K -1s ...diffracted light, K 0s ...diffracted light, K 1s ...diffracted light, K 2s ...diffracted light, Ki …Incoming light, L1…Outgoing light, L1…Series inductance, L1a…First divided light, L1b…Second divided light, L2…Reference light, L3…Object light, N…Normal, P…Pitch, R1…Equivalent series resistance, Rd…Limiting resistance, Rf…Feedback resistance, S(t)…Preprocessing Signal, 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, sin(θ m (t))...sine wave signal, Sa...amplitude signal, Sd...drive signal, Ss...reference signal, Vcc...terminal, X1...terminal, X2...terminal, Y...terminal, i...signal i, jp1...branch, jp2...branch, ps1...first signal path, ps2...second signal path, r...signal r, x...signal x, y...signal y, β...incident angle, θ B …blaze angle, θ S …Tilt angle

Claims

1. a laser light source that emits a first laser beam; a vibration element, the vibration element being used to modulate the first laser light, and a modulation signal being included an optical modulator for generating a second laser beam; a third laser including a sample signal generated by the first laser light being reflected by the object to be measured; a light receiving element that receives the first laser beam and the second laser beam and outputs a light receiving signal; a calculation unit that calculates the displacement and velocity of the object to be measured from the light receiving signal based on a reference signal; 、 Equipped with The calculation unit By multiplying the received light signal by a quadrature signal, it becomes closer to a signal with only frequency modulation. a preprocessing unit that outputs a preprocessed signal; The phase of the sine wave signal sin(θm(t)), which is one of the quadrature signals, is added to the pre-processed signal. The inverted signal -sin(θm(t)) is mixed to output a signal y, which is one of the mixed signals. The pre-processed signal is mixed with a cosine wave signal cos(θm(t)), which is another of the quadrature signals. and outputs a signal x, which is another one of the mixed signals, and outputs a tan(y / x). a preparation processing section; Adjusting the phase of the reference signal based on the amplitude of the preprocessed signal or the amplitude of the mixed signal an orthogonal signal generating unit that generates the orthogonal signal by and By calculating the atan(y / x), the displacement and velocity of the object to be measured can be calculated. A laser interferometer characterized by the above.

2. The orthogonal signal generation unit generates the orthogonal signal from the amplitude of the preprocessed signal or the amplitude of the mixed signal.

2. The laser interferometer according to claim 1, further comprising a phase amount setting unit for setting the phase of the signal.

3. The phase amount setting unit sets a maximum value of the amplitude of the preprocessing signal and a minimum value of the amplitude of the preprocessing signal. or the difference between the maximum value of the amplitude of the mixed signal and the minimum value of the amplitude of the mixed signal; 3. The laser according to claim 2, wherein the phases of the orthogonal signals are set so that the difference between Zur interferometer.

4. The orthogonal signal generation unit a Hilbert transform filter that performs Hilbert transform processing on the reference signal to obtain a signal i; 、 a reference signal delay circuit for delaying the reference signal to obtain a signal r; A reference signal obtained by performing an arctangent operation on the ratio of the signal i / the signal r to obtain the phase of the reference signal. a phase calculator; 4. The laser interferometer according to claim 1, further comprising:

5. 10. The demodulation processing unit according to claim 1, further comprising a mixed signal amplitude calculator for obtaining the amplitude of the mixed signal.

5. The laser interferometer according to any one of claims 1 to 4.

6. an oscillator circuit that outputs the reference signal; 6. The oscillator according to claim 1, wherein the vibration element is a signal source of the oscillator circuit. Laser interferometer.

7. 7. The laser interferometer according to claim 6, wherein the vibration element is a quartz crystal vibrator.

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