laser interferometer

Abstract

Provided is a laser interferometer capable of suppressing return light from being incident on a laser light source and suppressing a decrease in precision of demodulation of a sample signal originating from a measurement target object from a light-received signal. A laser interferometer characterized by comprising: a laser light source that emits laser light; a shielding element that has an opening through which the laser light passes; a light modulator that modulates the laser light into reference light having different frequencies; and a light-receiving element that receives object light generated by reflection of the laser light by a measurement target object and the reference light, and outputs a light-received signal, wherein when a diameter of the opening is set to D, the following is satisfied:

Description

Technical Field

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

[0002] Patent Document 1 discloses a laser vibrator as a device for measuring the vibration velocity of an object. This laser vibrator irradiates the object being measured with a laser beam and measures the vibration velocity based on the scattered laser beam subjected to a Doppler frequency shift.

[0003] Specifically, the laser vibrator described in Patent Document 1 includes an acousto-optic modulator (AOM). The acousto-optic modulator shifts the frequency of the laser by changing the frequency of the supplied ultrasonic wave. The laser vibrator uses the frequency-shifted laser as a reference light. Then, the scattered laser light from the object being measured is superimposed with the reference light from the acousto-optic modulator, and the beat frequency is extracted. The vibration velocity of the object being measured is determined from the extracted beat frequency.

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

[0005] In laser sources, laser oscillations can sometimes become unstable due to the intrusion of reflected light. In the laser vibrator described in Patent Document 1, when the laser oscillation becomes unstable, the quality of the laser decreases. Consequently, the signal-to-noise ratio (S / N ratio) decreases in the laser vibrator, or the phase of the oscillating laser becomes discontinuous. As a result, there is a technical problem of decreased accuracy in measuring the vibration velocity of an object. Summary of the Invention

[0006] The laser interferometer described in the application examples of this invention is characterized by having:

[0007] Laser source, emits laser light;

[0008] A shielding element having an opening for the laser to pass through;

[0009] An optical modulator modulates the laser light into reference light of different frequencies; and

[0010] The light-receiving element receives the object light generated by the laser reflected from the object being measured, as well as the reference light, and outputs a light-receiving signal.

[0011] When the diameter of the opening is set to At that time, the laser interferometer satisfies Wherein, the diameter of the opening The unit is mm. Attached Figure Description

[0012] Figure 1This is a functional block diagram illustrating the laser interferometer according to the first embodiment.

[0013] Figure 2 It is shown Figure 1 The diagram shows a simplified configuration of the sensor head.

[0014] Figure 3 It is shown Figure 2 A perspective view of a first example of a light modulator.

[0015] Figure 4 This is a top view showing a portion of a second configuration example of an optical modulator.

[0016] Figure 5 This is a top view showing a third configuration example of an optical modulator.

[0017] Figure 6 This explains when the incident light K i A conceptual diagram illustrating the generation of multiple diffracted beams when incident from a direction perpendicular to the surface of the vibrating element.

[0018] Figure 7 This explains the composition of the incident light K. i A conceptual diagram of an optical modulator whose direction of travel is 180° from the direction of travel of the reference light L2.

[0019] Figure 8 This explains the composition of the incident light K. i A conceptual diagram of an optical modulator whose direction of travel is 180° from the direction of travel of the reference light L2.

[0020] Figure 9 This explains the composition of the incident light K. i A conceptual diagram of an optical modulator whose direction of travel is 180° from the direction of travel of the reference light L2.

[0021] Figure 10 This is a cross-sectional view showing an optical modulator with a packaged structure.

[0022] Figure 11 This is a circuit diagram showing the configuration of a primary inverter oscillation circuit.

[0023] Figure 12 This is an example of the LCR equivalent circuit of a vibrating element.

[0024] Figure 13 It shows from Figure 2 The diagram shows the light trail of the emitted light L1 from the laser source and the reference light L2 generated by the reflection of the emitted light L1 by the optical modulator as the light trail of the return light L5 heading back to the laser source.

[0025] Figure 14This is a simplified configuration diagram showing the sensor head of the laser interferometer according to the second embodiment.

[0026] Figure 15 It shows from Figure 14 The diagram shows the light trail of the emitted light L1 from the laser source and the reference light L2 generated by the reflection of the emitted light L1 by the optical modulator as the light trail of the return light L5 heading back to the laser source.

[0027] Figure 16 This is a simplified structural diagram showing the mounting structure of the optical system of the laser interferometer involved in the first modified example.

[0028] Figure 17 This is a simplified structural diagram showing the mounting structure of the optical system of the laser interferometer involved in the second variation.

[0029] Figure 18 This is a simplified configuration diagram showing the mounting structure of the optical system of the laser interferometer involved in the third variation.

[0030] Figure 19 This is a simplified configuration diagram showing the mounting structure of the optical system of the laser interferometer involved in the fourth variation.

[0031] Figure 20 This is a simplified structural diagram showing the optical system of the laser interferometer involved in the fifth modification.

[0032] Explanation of reference numerals in the attached figures

[0033] 1…Laser interferometer, 2…Laser source, 3…Collimating lens, 4…Polarizing beam splitter, 4a…Polarizing beam splitter, 4b…Polarizing beam splitter, 4c…Polarizing beam splitter, 6…1 / 4 wavelength plate, 7…1 / 2 wavelength plate, 8…1 / 4 wavelength plate, 9…Analyzer, 10…Light receiving element, 12…Optical modulator, 12H…Optical modulator, 14…Object to be measured, 16…Setting part, 17…Shielding element, 18…Optical path, 20…Optical path, 22…Optical path, 24…Optical path, 30…Vibrating element, 30A…Vibrating element, 30B…Vibrating element, 3 1…Substrate, 32…Groove, 33…Pad, 34…Diffraction grating, 35…Pad, 36…Vibration direction, 37…Mirror, 39…Substrate, 40…Prism, 41…Mirror, 42…Prism, 44…Collimating lens, 45…Circuit element, 50…Optical system, 50D…Optical system, 50E…Optical system, 50F…Optical system, 50G…Optical system, 50H…Optical system, 51…Sensor head, 52…Demodulation circuit, 53…Preprocessing unit, 54…Oscillation circuit, 55…Demodulation processing unit, 70…Container, 72…Container body 74…cap, 76…bonding line, 120…optical modulation oscillator, 172…opening, 301…first electrode, 302…second electrode, 303…diffraction grating mounting portion, 305…piezoelectric substrate, 306…comb-shaped electrode, 307…ground electrode, 311…surface, 312…back side, 531…current-to-voltage converter, 532…ADC, 533…ADC, 534…first bandpass filter, 535…second bandpass filter, 536…first delay adjuster, 537…second delay adjuster, 538…multiplier, 539…third bandpass filter 540… First AGC, 541… Second AGC, 542… Adder, 551… Multiplier, 552… Multiplier, 553… Phase Shifter, 555… First Low-Pass Filter, 556… Second Low-Pass Filter, 557… Divider, 558… Arctangent Operator, 559… Output Circuit, 721… First Recess, 722… Second Recess, A1… First Optical Axis, A2… Second Optical Axis, C0… Parallel Capacitor, C1… Series Capacitor, C3… Third Capacitor, Cd… Second Capacitor, Cg… First Capacitor, GND… GND Terminal, K -2s …diffraction light, K -1s …diffraction light, K 0s …diffraction light, K 1s …diffraction light, K 2s …diffraction light, K i…Incident light, L1…Series inductance, L1…Outgoing light, L1a…Reflected light, L1b…Transmitted light, L2…Reference light, L3…Object light, L4…Object reference light, L5…Return light, N…Normal, P…Pitch, R1…Equivalent series resistance, Rd…Limiting resistance, Rf…Feedback resistance, S1…First signal, S2…Second signal, Sd…Drive signal, Ss…Reference signal, Vcc…Terminal, X1…Terminal, X2…Terminal, Y…Terminal, jp1…Branch, jp2…Branch, ps1…First signal path, ps2…Second signal path, x…Signal, y…Signal, Δy…Offset amplitude, β…Angle of incidence, θ′…Offset angle, θ B …flare angle, θ S …tilt angle. Detailed Implementation

[0034] The laser interferometer of the present invention will now be described in detail based on the embodiments shown in the accompanying drawings.

[0035] 1. First Implementation Method

[0036] First, the laser interferometer involved in the first embodiment will be described.

[0037] Figure 1 This is a functional block diagram illustrating the laser interferometer according to the first embodiment.

[0038] Figure 1 The laser interferometer 1 shown has: a sensor head 51, which includes an optical system 50 and an oscillation circuit 54; and a demodulation circuit 52, on which the light received from the optical system 50 is input.

[0039] 1.1. Sensor Head

[0040] Figure 2 It is shown Figure 1 A simplified structural diagram of the sensor head 51 is shown.

[0041] 1.1.1. Optical System

[0042] As previously mentioned, the sensor head 51 has an optical system 50.

[0043] like Figure 2 As shown, the optical system 50 includes: a laser source 2, a collimating lens 3, a polarizing beam splitter 4 (optical splitter), a quarter-wave plate 6, a quarter-wave plate 8, an analyzer 9, a light receiving element 10, a frequency-shifting optical modulator 12, a mounting part 16 on which the object to be measured 14 is disposed, and a blocking element 17.

[0044] Laser source 2 emits outgoing light L1 (laser) of a specified wavelength. Light receiving element 10 converts the received light into an electrical signal. Optical modulator 12, equipped with a vibrating element 30, modulates the outgoing light L1 to generate reference light L2 containing the modulation signal. Mounting unit 16 can be configured as needed to position the object to be measured 14. The outgoing light L1 incident on the object to be measured 14 is reflected as object light L3 containing the Doppler signal, i.e., the sampling signal, originating from the object to be measured 14.

[0045] The optical path of the emitted light L1 from the laser source 2 is designated as optical path 18. Optical path 18 is combined with optical path 20 by reflection from polarizing beam splitter 4. A quarter-wave plate 8 and an optical modulator 12 are sequentially arranged on optical path 20, starting from the polarizing beam splitter 4 side. Furthermore, optical path 18 is combined with optical path 22 by transmission from polarizing beam splitter 4. A quarter-wave plate 6 and a mounting portion 16 are sequentially arranged on optical path 22, starting from the polarizing beam splitter 4 side.

[0046] Optical path 20 is combined with optical path 24 through the transmission of polarization beam splitter 4. On optical path 24, starting from the side of polarization beam splitter 4, analyzer 9 and light receiving element 10 are arranged in sequence.

[0047] The emitted light L1 from the laser source 2 passes through optical paths 18 and 20 and is incident on the optical modulator 12. Additionally, the emitted light L1 passes through optical paths 18 and 22 and is incident on the object to be measured 14. The reference light L2 generated by the optical modulator 12 passes through optical paths 20 and 24 and is incident on the light-receiving element 10. The object light L3 generated by reflection from the object to be measured 14 passes through optical paths 22 and 24 and is incident on the light-receiving element 10.

[0048] It should be noted that, in this specification, "optical path" refers to the path of light traveling between optical components. Furthermore, "optical axis" as used later refers to the central axis of the light beam passing through the optical path.

[0049] The following is a further explanation of each part of the optical system 50.

[0050] 1.1.1.1. Laser source

[0051] Laser source 2 is a laser source that emits interferometric outgoing light L1. Laser source 2 preferably uses a light source with a linewidth of MHz or less. Specifically, examples include gas lasers such as He-Ne lasers, semiconductor laser elements such as DFB-LD (Distributed feedback-laser diode), FBG-LD (laser diode with fiber bragg grating), VCSEL (Vertical Cavity Surface Emitting Laser), and FP-LD (Fabry-Perot Laser Diode).

[0052] The laser source 2 is preferably a semiconductor laser element. This allows for significant miniaturization of the laser source 2. Consequently, miniaturization of the laser interferometer 1 is achieved. In particular, the miniaturization and weight reduction of the sensor head 51 housing the optical system 50 in the laser interferometer 1 also improves the operability of the laser interferometer 1.

[0053] 1.1.1.2. Collimating Lens

[0054] Collimating lens 3 is a convex lens disposed between laser source 2 and polarizing beam splitter 4. Collimating lens 3 makes the outgoing light L1 emitted from laser source 2 parallel.

[0055] It should be noted that if the outgoing light L1 emitted from the laser source 2 has been sufficiently parallelized, for example, if a gas laser such as a He-Ne laser is used as the laser source 2, the collimating lens 3 can be omitted.

[0056] 1.1.1.3. Polarized Beam Splitter

[0057] The polarization beam splitter 4 is an optical divider disposed between the laser source 2 and the optical modulator 12, and between the laser source 2 and the object to be measured 14. The polarization beam splitter 4 splits the emitted light L1 into reflected light L1a (first split light) and transmitted light L1b (second split light). Furthermore, the polarization beam splitter 4 has the function of transmitting P-polarized light and reflecting S-polarized light. Hereinafter, we consider the case where the emitted light L1, which is linearly polarized light and has a P-polarized light to S-polarized light ratio of, for example, 50:50, is incident on the polarization beam splitter 4.

[0058] The reflected light L1a, which is S-polarized light and is reflected by the polarization beam splitter 4, is converted into circularly polarized light by the quarter-wave plate 8 and then incident on the optical modulator 12. The circularly polarized light L1a incident on the optical modulator 12 is subjected to f m A frequency shift of [Hz] is observed, and this is reflected as reference light L2. Therefore, reference light L2 contains frequency f. m The modulation signal is [Hz]. When the reference light L2 passes through the quarter-wave plate 8 again, it is converted into P-polarized light. The P-polarized light of the reference light L2 passes through the polarization beam splitter 4 and the analyzer 9 and is incident on the light receiving element 10.

[0059] The transmitted light L1b, which is P-polarized light, passing through the polarizing beam splitter 4, is converted into circularly polarized light by the quarter-wave plate 6 and incident on the active measurement object 14. The circularly polarized light L1b incident on the measurement object 14 is subjected to f d The Doppler frequency shift of [Hz] is reflected as object light L3. Therefore, object light L3 contains frequency f. d The sampling signal is [Hz]. When the object light L3 passes through the 1 / 4 wavelength plate 6 again, it is converted into S-polarized light. The S-polarized light of the object light L3 is reflected by the polarization beam splitter 4, passes through the analyzer 9, and is incident on the light receiving element 10.

[0060] As mentioned earlier, since the outgoing light L1 is interferometric, the reference light L2 and the object light L3 are incident on the light receiving element 10 as interference light.

[0061] It should be noted that a non-polarized beam splitter can also be used instead of a polarized beam splitter. In this case, the quarter-wave plate 6 and the quarter-wave plate 8 are no longer needed, thus enabling miniaturization of the laser interferometer 1 due to the reduction in the number of components. Alternatively, a beam splitter other than the polarized beam splitter 4 can also be used.

[0062] 1.1.1.4. Analyzer

[0063] Since the S-polarized and P-polarized beams are orthogonal and independent, their simple superposition will not produce beats due to interference. Therefore, the superimposed S-polarized and P-polarized beams are passed through an analyzer 9 tilted at 45° relative to both beams. By using the analyzer 9, beams with common components can pass through and interfere. As a result, in the analyzer 9, the reference beam L2 interferes with the object beam L3, generating a beam with |f|. m -f d Interference light with a frequency of [Hz].

[0064] 1.1.1.5. Light-receiving element

[0065] Reference light L2 and object light L3 are incident on the light-receiving element 10 via polarization beam splitter 4 and analyzer 9. The reference light L2 and object light L3 undergo optical heterodyne interference, resulting in a beam with |f|. m -f d Interference light with a frequency of [Hz] is incident on the light-receiving element 10. By demodulating the sampled signal from this interference light using the method described later, the motion, i.e., vibration velocity and displacement, of the object 14 to be measured can be determined. Examples of light-receiving elements 10 include photodiodes.

[0066] 1.1.1.6. Optical Modulator

[0067] Figure 3 It is shown Figure 2 A perspective view of a first configuration example of the optical modulator 12 shown.

[0068] 1.1.1.6.1. Summary of the First Configuration Example of an Optical Modulator

[0069] The frequency-shifting optical modulator 12 has an optical modulation oscillator 120. Figure 3 The optical modulation oscillator 120 shown includes a plate-shaped vibrating element 30 and a substrate 31 that supports the vibrating element 30.

[0070] The vibrating element 30 is made of a material that repeatedly vibrates in a manner that deforms along the direction of its surface when an electrical potential is applied. In this configuration example, the vibrating element 30 is a crystal AT oscillator that vibrates with thickness shear along the vibration direction 36 in the high-frequency region of the MHz band. A diffraction grating 34 is formed on the surface of the vibrating element 30. The diffraction grating 34 has a structure consisting of a plurality of straight grooves 32 that are periodically arranged and have components that intersect the vibration direction 36, i.e., a component that intersects the vibration direction 36.

[0071] The substrate 31 has a surface 311 and a back surface 312, which are mutually adjacent. A vibrating element 30 is disposed on the surface 311. In addition, a pad 33 for applying a potential to the vibrating element 30 is provided on the surface 311. On the other hand, a pad 35 for applying a potential to the vibrating element 30 is also provided on the back surface 312.

[0072] The size of the substrate 31 is, for example, set to have a long side of 0.5 mm or more and 10.0 mm or less. Additionally, the thickness of the substrate 31 is, for example, set to have a thickness of 0.10 mm or more and 2.0 mm or less. As an example, the shape of the substrate 31 is set to be a square with a side length of 1.6 mm, and its thickness is set to 0.35 mm.

[0073] The size of the vibrating element 30 is, for example, set to have a long side of 0.2 mm or more and 3.0 mm or less. In addition, the thickness of the vibrating element 30 is, for example, set to have a thickness of 0.003 mm or more and 0.5 mm or less.

[0074] As an example, the vibrating element 30 is shaped as a square with a side length 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. It should be noted that by changing the thickness of the vibrating element 30 or taking into account harmonics (overtones), the oscillation frequency can be adjusted in the range of 1 MHz to 1 GHz.

[0075] It should be noted that, although in Figure 3 The diffraction grating 34 is formed on the entire surface of the vibrating element 30, but it may also be formed on only a portion of it.

[0076] The magnitude of the optical modulation performed by the optical modulator 12 is given by the inner product of the difference wavenumber vector of the wavenumber vector of the outgoing light L1 incident on the optical modulator 12 and the wavenumber vector of the reference light L2 emitted from the optical modulator 12, and the vector of the vibration direction 36 of the vibrating element 30. Although the vibrating element 30 performs thickness shear vibration in this configuration example, since this vibration is in-plane vibration, optical modulation cannot be performed even if light is incident perpendicularly to the surface of the vibrating element 30. Therefore, in this configuration example, by providing a diffraction grating 34 on the vibrating element 30, optical modulation can be performed according to the principle described later.

[0077] Figure 3 The diffraction grating 34 shown is a blazed diffraction grating. A blazed diffraction grating is a diffraction grating with a sub-step shape in cross-section. The straight grooves 32 of the diffraction grating 34 are configured such that their extension direction is orthogonal to the vibration direction 36.

[0078] When from Figure 1 and Figure 2 The oscillation circuit 54 shown is directed towards Figure 3 When the vibrating element 30 shown is supplied with a drive signal Sd (an AC voltage is applied), the vibrating element 30 oscillates. The power (drive power) required for the oscillation of the vibrating element 30 is not particularly limited, but is as low as about 0.1 μW to 100 mW. Therefore, it can be used to make the vibrating element 30 oscillate without amplifying the drive signal Sd output from the oscillation circuit 54.

[0079] Furthermore, existing optical modulators sometimes require structures to maintain their temperature, making it difficult to reduce their size. Additionally, existing optical modulators have high power consumption, posing a technical challenge for miniaturizing and reducing the power consumption of laser interferometers. In contrast, in this configuration example, because the oscillation element 30 is very small and requires little power for oscillation, miniaturization and power saving of the laser interferometer 1 are easily achieved.

[0080] 1.1.1.6.2. Methods for forming diffraction gratings

[0081] The method for forming the diffraction grating 34 is not particularly limited. As an example, the following method can be listed: a mold is made using a mechanical scribing method (scrubbing machine), and a groove 32 is formed on the electrode of the vibrating element 30 of the crystal AT oscillator by nanoimprinting. Here, the reason for forming it on the electrode is that, in the case of the crystal AT oscillator, high-quality thickness shear vibration can theoretically be generated on the electrode. It should be noted that the groove 32 is not limited to being formed on the electrode; it can also be formed on the surface of the material in the non-electrode portion. In addition, processing methods based on exposure and etching, electron beam lithography, focused ion beam processing (FIB), etc., can be used instead of nanoimprinting.

[0082] Alternatively, a diffraction grating can be formed on the chip of the crystal AT oscillator using a photoresist material, and a mirror film composed of a metal film and a dielectric multilayer film can be placed there. By adding the metal film and the mirror film, the reflectivity of the diffraction grating 34 can be improved.

[0083] Furthermore, a resist film can be formed on the chip or wafer of the crystal AT oscillator. After etching, the resist film is removed, and then a metal film or mirror film is formed on the processed surface. In this case, since the resist material is removed, the effects caused by the resist material's moisture absorption are eliminated, thus improving the chemical stability of the diffraction grating 34. In addition, by setting a highly conductive metal film such as Au or Al, it can also be used as an electrode to drive the oscillation element 30.

[0084] It should be noted that the diffraction grating 34 can also be formed using techniques such as anodic alumina (porous alumina).

[0085] 1.1.1.6.3. Other configuration examples of optical modulators

[0086] The vibrating element 30 is not limited to a crystal oscillator; for example, it can also be a Si oscillator, a surface wave (SAW) device, a ceramic oscillator, etc.

[0087] Figure 4 This is a top view showing a portion of a second configuration example of the optical modulator 12. Figure 5This is a top view showing a third configuration example of the optical modulator 12.

[0088] Figure 4 The vibrating element 30A shown is a Si oscillator manufactured from a Si substrate using MEMS technology. MEMS (Micro Electro Mechanical Systems) is a type of microelectromechanical system.

[0089] The vibrating element 30A includes: a first electrode 301 and a second electrode 302, which are adjacent to each other on the same plane with a gap between them; a diffraction grating mounting portion 303 disposed on the first electrode 301; and a diffraction grating 34 disposed on the diffraction grating mounting portion 303. The first electrode 301 and the second electrode 302 are driven, for example, by electrostatic attraction. Figure 4 The left and right directions, that is, along Figure 4 The axis connecting the first electrode 301 and the second electrode 302 vibrates repeatedly, approaching and separating from each other. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the Si oscillator is, for example, around 1 kHz to several hundred MHz.

[0090] Figure 5 The vibrating element 30B shown is a SAW device that utilizes surface waves. SAW (Surface Acoustic Wave) is an elastic surface wave.

[0091] The vibrating element 30B includes a piezoelectric substrate 305, a comb-shaped electrode 306 disposed on the piezoelectric substrate 305, a ground electrode 307, a diffraction grating mounting portion 303, and a diffraction grating 34. When an alternating voltage is applied to the comb-shaped electrode 306, an elastic surface wave is excited through the inverse piezoelectric effect. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the SAW device is, for example, from several hundred MHz to several GHz.

[0092] For devices like the above, by setting up a diffraction grating 34, optical modulation can be performed according to the principle described later, just as with the crystal AT oscillator.

[0093] On the other hand, when the vibrating element 30 is a crystal oscillator, the extremely high Q value of the crystal enables the generation of a high-precision modulation signal. The Q value is an indicator of the sharpness of the resonance peak. In addition, crystal oscillators are not easily affected by external interference. Therefore, by using the modulation signal modulated by the optical modulator 12 equipped with a crystal oscillator, the sampling signal from the measurement object 14 can be acquired with high precision.

[0094] 1.1.1.6.4. Optical modulation using vibrating elements

[0095] Next, the principle of using the vibrating element 30 to modulate light will be explained.

[0096] Figure 6 This explains when the incident light K i A conceptual diagram illustrating the generation of multiple diffracted beams when incident from a direction perpendicular to the surface of the vibrating element 30.

[0097] When the incident light K i When incident on a diffraction grating 34 that undergoes thickness shear vibration along the vibration direction 36, due to diffraction phenomena, such as... Figure 6 As shown, multiple diffracted beams K are generated. ns n is the diffracted light K ns The number of times, n = 0, ±1, ±2... It should be noted that... Figure 6 The diffraction grating 34 shown is not Figure 3 Instead of showing a blazed diffraction grating, this illustration, as an example of other diffraction gratings, depicts a diffraction grating formed by repeating concave and convex shapes. Furthermore, in Figure 6 In the text, the diffraction light K is omitted. 0s The illustration.

[0098] exist Figure 6 In the middle, the incident light K i The light is incident from a direction perpendicular to the surface of the vibrating element 30, but this incident angle is not particularly limited; the incident angle can also be set by incident at an angle relative to the surface of the vibrating element 30. In the case of oblique incident light, the diffracted light K ns Its direction of travel also changes accordingly.

[0099] It should be noted that, due to the design of the diffraction grating 34, higher-order light (|n|≥2) may not sometimes appear. Therefore, to obtain a stable modulation signal, it is ideal to set |n| = 1. That is, in Figure 2 In the laser interferometer 1, the frequency-shifting optical modulator 12 is preferably configured to use ±1st order diffracted light as reference light L2. This configuration enables the stabilization of measurements by the laser interferometer 1.

[0100] On the other hand, when higher-order light with |n|≥2 appears from the diffraction grating 34, the optical modulator 12 can be configured to use any diffraction light of ±2nd order or higher as the reference light L2, instead of ±1st order diffraction light. Thus, higher-order diffraction light can be utilized, thereby enabling the laser interferometer 1 to achieve higher frequency and smaller size.

[0101] In this embodiment, as an example, incident light K incident on the light modulator 12 i The optical modulator 12 is configured such that the angle between the direction of entry of the light and the direction of travel of the reference light L2 emitted from the optical modulator 12 is 180°. Three examples will be described below.

[0102] Figures 7 to 9 These are respectively the incident light K i A conceptual diagram illustrating an optical modulator 12 whose direction of travel forms an angle of 180° with the direction of travel of the reference light L2.

[0103] Figure 7 The optical modulator 12 shown includes a reflector 37 in addition to the vibrating element 30. The reflector 37 is configured to reflect the diffracted light K. 1s And it returns to the diffraction grating 34. At this time, the diffracted light K 1s The angle between the incident angle and the reflection angle at mirror 37 is 180°. As a result, the diffracted light K emitted from mirror 37 and returning to diffraction grating 34... 1s The light is diffracted again by the diffraction grating 34, and then directed towards the incident light K that is incident on the light modulator 12. i It travels in the opposite direction to the direction of travel. Therefore, by adding a reflector 37, the above-mentioned incident light K can be satisfied. i The condition that the angle between the direction of entry of the light and the direction of travel of the reference light L2 is 180°.

[0104] Furthermore, the reference light L2 generated by the optical modulator 12 is subjected to two frequency modulations via the reflector 37. Therefore, compared to using the vibrating element 30 alone, higher frequency modulation can be achieved by using the reflector 37 in conjunction with the vibrating element 30.

[0105] exist Figure 8 In, relative to Figure 6 The configuration causes the vibrating element 30 to tilt. The tilt angle θ at this point... S The incident light K is set to satisfy the above conditions. i The condition that the angle between the direction of entry of the light and the direction of travel of the reference light L2 is 180°.

[0106] Figure 9 The diffraction grating 34 shown has a blaze angle θ B A blazed diffraction grating. Then, incident light K travels at an incident angle β relative to the normal N of the surface of the vibrating element 30. i When incident on diffraction grating 34, reference light L2 is relative to the normal N with a blaze angle θ. B The same angle returns. Therefore, by making the incident angle β the same as the blaze angle θ B Equal, able to satisfy the above-mentioned incident light K i The condition that the angle between the direction of entry of the light beam and the direction of travel of the reference light L2 is 180°. In this case, it is not used. Figure 7 The reflector 37 shown, and as Figure 8As shown, the condition can be satisfied without tilting the vibrating element 30 itself, thus enabling further miniaturization and high-frequency operation of the laser interferometer 1. Especially in the case of a blazed diffraction grating, the configuration that satisfies the condition is called the "Litterow configuration," which also has the advantage of significantly improving the diffraction efficiency of the diffracted light.

[0107] It should be noted that, Figure 9 The pitch P represents the pitch of the blazed diffraction grating; as an example, the pitch P is 1 μm. Additionally, the blaze angle θ... B For example, 25°. In this case, to satisfy the condition, it is only necessary to make the incident light K... i The incident angle β relative to the normal N should also be 25°.

[0108] 1.1.1.6.5. Packaging Structure

[0109] Figure 10 This is a cross-sectional view showing an optical modulator 12 with an encapsulation structure.

[0110] Figure 10 The optical modulator 12 shown includes a container 70 as a frame, an optical modulation oscillator 120 housed in the container 70, and circuit elements 45 constituting an oscillation circuit 54. It should be noted that the container 70 is, for example, hermetically sealed in a reduced pressure atmosphere such as a vacuum or in an inert gas atmosphere such as nitrogen or argon.

[0111] like Figure 10 As shown, the container 70 has a container body 72 and a lid 74. The container body 72 has a first recess 721 disposed inside it and a second recess 722 disposed inside the first recess 721 and deeper than the first recess 721. The container body 72 is made of, for example, a ceramic material or a resin material. Furthermore, although not shown, the container body 72 includes internal terminals disposed on its inner surface, external terminals disposed on its outer surface, and wiring connecting the internal and external terminals.

[0112] Furthermore, the opening of the container body 72 is sealed by the cap 74 via a sealing ring (not shown), low-melting-point glass, or other sealing components. The cap 74 is made of a material that is transparent to laser light, such as glass.

[0113] An 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). In addition, the internal terminals of the container body 72 are electrically connected to the optical modulation oscillator 120, for example, via a conductive material (not shown) such as a bonding wire or a bonding metal.

[0114] A circuit element 45 is disposed on the bottom surface of the second recess 722. The circuit element 45 is electrically connected to the internal terminals of the container body 72 via a bonding wire 76. Thus, the optical modulation oscillator 120 and the circuit element 45 are also electrically connected via wiring provided in the container body 72. It should be noted that circuitry other than the oscillation circuit 54 described later may also be provided in the circuit element 45.

[0115] By employing this packaging structure, the optical modulation oscillator 120 and the circuit element 45 can be overlapped, thus bringing their physical distance closer and shortening the wiring length between them. Therefore, it is possible to suppress noise from the outside entering the drive signal Sd, or conversely, to prevent the drive signal Sd from becoming a noise source. Furthermore, a container 70 can protect both the optical modulation oscillator 120 and the circuit element 45 from the influence of the external environment. Therefore, it is possible to both miniaturize the sensor head 51 and improve the reliability of the laser interferometer 1.

[0116] It should be noted that the structure of container 70 is not limited to the structure shown in the figure. For example, the optical modulation oscillator 120 and circuit element 45 can also have separate packaging structures. Additionally, although not shown, other circuit elements constituting the oscillation circuit 54 can also be accommodated in container 70. It should be noted that container 70 can be provided as needed or omitted.

[0117] Furthermore, the optical modulator 12 is not limited to an optical modulator with a vibrating element 30 as described above; for example, it can also be an acousto-optic modulator (AOM), an electro-optic modulator (EOM), etc. It should be noted that when an AOM or EOM is applied to the optical modulator 12, a light reflection function can also be added to the AOM or EOM.

[0118] 1.1.1.7. Obstruction element

[0119] The blocking element 17 is an iris disposed between the collimating lens 3 and the polarizing beam splitter 4. The blocking element 17 has an opening 172 corresponding to the optical path 18. The blocking element 17 suppresses the backlight L5 generated by the optical modulator 12, the object to be measured 14, etc., from incident on the laser source 2. Since the blocking element 17 only needs to function as a blocker of the backlight L5, its structure is very simple. Therefore, it contributes to the simplification of the structure of the laser interferometer 1. It should be noted that the blocking element 17 can also be a slit, a pinhole, etc., and its structure is not particularly limited.

[0120] The function and effect of the blocking element 17 will be described in detail later.

[0121] 1.1.2. Oscillator Circuit

[0122] like Figure 1As shown, the oscillation circuit 54 outputs a drive signal Sd that is input to the optical modulator 12 of the optical system 50. Additionally, the oscillation circuit 54 outputs a reference signal Ss that is input to the demodulation circuit 52.

[0123] The oscillation circuit 54 is not particularly limited as long as it is a circuit that can make the oscillating element 30 oscillate; various circuit configurations can be used. Figure 11 This is a circuit diagram showing the configuration of a single-stage inverter oscillator circuit as an example of circuit configuration.

[0124] Figure 11 The oscillation circuit 54 shown includes circuit element 45, feedback resistor Rf, limiting resistor Rd, first capacitor Cg, second capacitor Cd, and third capacitor C3.

[0125] Circuit element 45 is an inverter IC. Terminals X1 and X2 of circuit element 45 are respectively connected to the inverter terminals inside circuit element 45. Terminal GND is connected to the ground potential, and terminal Vcc is connected to the power supply potential. Terminal Y is used for oscillation output.

[0126] A first capacitor Cg is connected between terminal X1 and the ground potential. Additionally, a limiting resistor Rd and a second capacitor Cd, connected in series between terminal X2 and the ground potential, are connected sequentially 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 the limiting resistor Rd.

[0127] In addition, one end of the vibrating element 30 is connected between the first capacitor Cg and the feedback resistor Rf, and the other end of the vibrating element 30 is connected between the second capacitor Cd and the limiting resistor Rd. Thus, the vibrating element 30 becomes the signal source of the oscillation circuit 54.

[0128] Figure 12 This is an example of the LCR equivalent circuit of the vibrating element 30.

[0129] like Figure 12 As shown, the LCR equivalent circuit of the vibration element 30 consists of a series capacitor C1, a series inductor L1, an equivalent series resistance R1, and a parallel capacitor C0.

[0130] exist Figure 11 In the oscillation circuit 54 shown, when the capacitance of the first capacitor Cg is set to C... g Let the capacitance of the second capacitor Cd be C. d At that time, the load capacitance C L It is given by the following formula (a).

[0131]

[0132] Thus, the oscillation frequency f output from terminal Y of the oscillation circuit 54 osc It is given by the following formula (b).

[0133]

[0134] f Q It is the natural frequency of the vibrating element 30.

[0135] According to equation (b) above, by appropriately changing the load capacitance C L The oscillation frequency f of the signal output from terminal Y can be... osc Make minor adjustments.

[0136] In addition, the natural frequency f of the vibrating element 30 Q The oscillation frequency f of the oscillation circuit 54 osc The difference Δf is given by the following equation (c).

[0137]

[0138] Here, since C1 << C0 and C1 << C L Therefore, Δf is approximately given by the following equation (d).

[0139]

[0140] Therefore, the oscillation frequency f of the oscillation circuit 54 osc Becoming the natural frequency f of the vibrating element 30 Q The corresponding value.

[0141] Here, when the vibrating element 30 is fixed to, for example, the container 70, if it is subjected to expansion stress caused by temperature via the fixing part, the natural frequency f Q Changes occur. Furthermore, when the vibrating element 30 is tilted, it is affected by gravity and other forces generated by its own weight, causing its natural frequency f to change. Q Changes have occurred.

[0142] In the oscillator circuit 54, even if the inherent frequency f is due to such reason Q The change has occurred; based on the above equation (d), the oscillation frequency f osc It also changes in conjunction with this change. That is to say, the oscillation frequency f osc Always from the natural frequency f Q The value deviates from Δf. Therefore, the vibration of the vibrating element 30 is stable, and the displacement amplitude is stable. Because the displacement amplitude is stable, the modulation characteristics of the optical modulator 12 are stable, thus improving the demodulation accuracy of the sampled signal in the demodulation circuit 52.

[0143] As an example, the preferred value is Δf = |fosc -f Q |≤3000[Hz], further preferably 600[Hz].

[0144] As described above, in the laser interferometer 1 according to this embodiment, the optical modulator 12 includes a vibrating element 30. The optical modulator 12 uses the vibrating element 30 to modulate the reflected light L1a (laser).

[0145] Based on this configuration, the optical modulator 12 can be miniaturized and made lighter. Therefore, the laser interferometer 1 can be miniaturized and made lighter.

[0146] Furthermore, the laser interferometer 1 according to this embodiment includes a demodulation circuit 52 and an oscillation circuit 54. The oscillation circuit 54 includes a vibration element 30 as its signal source, such as... Figure 1 As shown, the demodulation circuit 52 outputs a reference signal Ss. Based on the reference signal Ss, the demodulation circuit 52 demodulates the sampled signal originating from the measured object 14 from the received light signal.

[0147] Based on this configuration, even if the natural frequency f of the vibrating element 30 is... Q The change can also affect the oscillation frequency f of the oscillation circuit 54. osc The change is related to the natural frequency f of the vibrating element 30. Q The corresponding values ​​allow for easy stabilization of the vibration of the vibrating element 30. This enables the temperature characteristics of the modulation signal to correspond to the temperature characteristics of the vibrating element 30, stabilizing the modulation characteristics of the optical modulator 12. Consequently, the demodulation accuracy of the sampled signal in the demodulation circuit 52 is improved.

[0148] Furthermore, in the above configuration, the temperature characteristics of the reference signal Ss output from the oscillation circuit 54 to the demodulation circuit 52 can also correspond to the temperature characteristics of the vibrating element 30. In this way, both the temperature characteristics of the modulation signal and the temperature characteristics of the reference signal correspond to the temperature characteristics of the vibrating element 30. Therefore, the changes in the modulation signal caused by temperature variations are consistent with or approximately similar to the changes in the reference signal Ss. Thus, even if the temperature of the vibrating element 30 changes, the impact on demodulation accuracy can be suppressed, and the demodulation accuracy of the sampled signal originating from the measurement object 14 can be improved.

[0149] Furthermore, in this embodiment, since the oscillation circuit 54 has low power consumption, it is easy to achieve power saving in the laser interferometer 1.

[0150] It should be noted that, in place of the oscillation circuit 54, signal generators such as function generators or signal generators can also be used.

[0151] 1.2. Demodulation Circuit

[0152] The demodulation circuit 52 performs demodulation processing on the sampled signal originating from the object to be measured 14, which is derived from the light-receiving signal output from the light-receiving element 10. The sampled signal includes, for example, phase information and frequency information. Furthermore, the displacement of the object to be measured 14 can be obtained from the phase information, and the velocity of the object to be measured 14 can be obtained from the frequency information. If different information can be obtained in this way, the laser interferometer 1 can be highly functionalized by having the functions of a displacement meter and a velocity meter.

[0153] The demodulation circuit 52 is configured according to the modulation processing method. In the laser interferometer 1 according to this embodiment, an optical modulator 12 equipped with a vibrating element 30 is used. Since the vibrating element 30 is a single vibrating element, its vibration speed changes constantly within the period. Therefore, the modulation frequency also changes with time, and existing demodulation circuits cannot be used as is.

[0154] Existing demodulation circuits, for example, refer to circuits that demodulate sampled signals from received optical signals containing modulated signals obtained using an acousto-optic modulator (AOM). In an acousto-optic modulator, the modulation frequency does not change. Therefore, existing demodulation circuits can demodulate sampled signals from received optical signals containing modulated signals with a fixed modulation frequency, but they cannot perform demodulation in the case of modulated signals containing modulated signals modulated by the optical modulator 12 with a changing modulation frequency.

[0155] therefore, Figure 1 The demodulation circuit 52 shown includes a preprocessing unit 53 and a demodulation processing unit 55. The light-receiving signal output from the light-receiving element 10 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 light-receiving signal. Through this preprocessing, a signal that can be demodulated by a conventional demodulation circuit can be obtained. Therefore, in the demodulation processing unit 55, the sampling signal originating from the object to be measured 14 is demodulated using a known demodulation method.

[0156] 1.2.1. Composition of the pretreatment unit

[0157] Figure 1 The preprocessing unit 53 shown includes a first bandpass filter 534, a second bandpass filter 535, a first delay adjuster 536, a second delay adjuster 537, a multiplier 538, a third bandpass filter 539, a first AGC 540, a second AGC 541, and an adder 542. It should be noted that AGC stands for Automatic Gain Control.

[0158] Between the light-receiving element 10 and the preprocessing unit 53, starting from the light-receiving element 10, a current-to-voltage converter 531 and an ADC 532 are connected in sequence. The current-to-voltage converter 531 is a transimpedance amplifier that converts the current output from the light-receiving element 10 into a voltage signal. The ADC 532 is an analog-to-digital converter that converts the analog signal into a digital signal with a specified number of sampling bits.

[0159] The current output from the light-receiving element 10 is converted into a voltage signal by a current-to-voltage converter 531. The voltage signal is then converted into a digital signal by an ADC 532, and split into two signals, a first signal S1 and a second signal S2, by a branch JP1. Figure 1 In this process, the path of the first signal S1 is set as the first signal path ps1, and the path of the second signal S2 is set as the second signal path ps2.

[0160] An ADC533 is connected between the oscillator circuit 54 and the second delay adjuster 537. The ADC533 is an analog-to-digital converter that converts analog signals into digital signals at a specified number of sampling bits.

[0161] The first bandpass filter 534, the second bandpass filter 535, and the third bandpass filter 539 are filters that selectively allow signals in specific frequency bands to pass through.

[0162] The first delay adjuster 536 and the second delay adjuster 537 are circuits that adjust the delay of the signals, respectively. The multiplier 538 is a circuit that generates an output signal proportional to the product of the two input signals. The adder 542 is a circuit that generates an output signal proportional to the sum of the two input signals.

[0163] Next, the operation of the preprocessing unit 53 will be explained along the flow of the first signal S1, the second signal S2, and the reference signal Ss.

[0164] After passing through the first bandpass filter 534 configured on the first signal path ps1, the group delay of the first signal S1 is adjusted by the first delay adjuster 536. The group delay adjusted by the first delay adjuster 536 is equivalent to the group delay of the second signal S2 generated by the second bandpass filter 535 (described later). Through this delay adjustment, the delay time accompanying the filter circuits can be made consistent between the first bandpass filter 534 through which the first signal S1 passes and the second bandpass filter 535 and third bandpass filter 539 through which the second signal S2 passes. The first signal S1, after passing through the first delay adjuster 536, is input to the adder 542 via the first AGC 540.

[0165] The second signal S2, after passing through the second bandpass filter 535 configured on the second signal path ps2, is input to the multiplier 538. In the multiplier 538, the second signal S2 is multiplied by the reference signal Ss output from the second delay adjuster 537. Specifically, the reference signal Ss output from the oscillator circuit 54, which is cos(ω... m The reference signal Ss, represented by t), is digitally converted by ADC533, phase-adjusted by the second delay adjuster 537, and then input to multiplier 538. ω m t is the angular frequency of the modulation signal of the optical modulator 12, and t is time. Then, the second signal S2 passes through the third bandpass filter 539 and is input to the adder 542 via the second AGC 541.

[0166] In the adder 542, an output signal proportional to the sum of the first signal S1 and the second signal S2 is output to the demodulation processing unit 55.

[0167] 1.2.2. Basic Principles of Preprocessing

[0168] Next, the basic principle of preprocessing in preprocessing unit 53 will be explained. It should be noted that the basic principle referred to here is the principle described in Japanese Patent Application Publication No. 2-38889. Furthermore, in the following explanation, as an example, a system in which the frequency of the modulation signal varies sinusoidally and the displacement of the object 14 being measured also varies with a single vibration along the optical axis will be considered. Here, E... m E d , It can be expressed by the following formula:

[0169] E m =a m {cos(ω0t+B sinω m t+φ m )+i sin(ω0t+B sinω m t+φ m )} (1)

[0170] E d =a d {cos(ω0t+A sinω d t+φ d )+i sin(ω0t+A sinω d t+φ d (2)

[0171] φ=φ m -φ d (3)

[0172] At that time, the light-receiving signal I output from the light-receiving element 10 pDTheoretically, it can be represented by the following formula.

[0173] I PD =<|E m +E d | 2 >

[0174] =<|E m 2 +E d 2 +2E m E d |>

[0175] =a m 2 +a d 2 +2a m a d cos(B sinω m tA sinω d t+φ) (4)

[0176] It should be noted that E m E d , ω m ω d , ω0, a m a d The details are as follows.

[0177] E m Electric field components of the modulation signal originating from the optical modulator

[0178] E d Electric field components originating from the sampling signal of the object being measured.

[0179] The initial phase of the modulation signal originating from the optical modulator

[0180] The initial phase of the sampling signal originating from the object being measured

[0181] Optical path phase difference of laser interferometer

[0182] ω m Angular frequency of the modulation signal originating from the optical modulator

[0183] ω d : The angular frequency derived from the sampling signal of the object being measured

[0184] ω0: Angular frequency of the emitted light from the light source

[0185] a m :coefficient

[0186] a d :coefficient

[0187] In addition, in equation (4), <> represents time average.

[0188] The first and second terms of equation (4) above represent the DC component, and the third term represents the AC component. When this AC component is set as I... PD·AC At that time, I PD·AC It is expressed by the following formula.

[0189] I PD·AC =2a m a d cos(B sinω m tA sinω d t+φ)

[0190] =2a m a d {cos(B sinω m t)cos(A sinω d t-φ)+sin(B sinω m t)sin(A sinω d t-φ)} (5)

[0191]

[0192]

[0193] A: Phase shift of the sampled signal

[0194] f dmax Doppler frequency shift of the sampled signal

[0195] f d Frequency of the sampled signal

[0196] B: Phase shift of the modulated signal

[0197] f mmax Doppler frequency shift of the modulated signal

[0198] f m Frequency of the modulating signal

[0199] Here, the following v-degree Bessel functions are known: equations (8) and (9).

[0200] cos{ζsin(2πf v t)}=J0(ζ)+2J2(ζ)cos(2·2πf v t)+2J4(ζ)cos(4·2πf vt)+… (8)

[0201] sin{ζsin(2πf v t)}=2J1(ζ)sin(1·2πf v t)+2J3(ζ)sin(3·2πf v t)+… (9)

[0202] If we use the Bessel functions of equations (8) and (9) to perform a series expansion of equation (5), it can be transformed into equation (10) as follows.

[0203] I PD.AC =2a m a d [{J0(B)+2J2(B)cos(2·ω m t)+2J4(B)cos(4·ω m t)+…}cos(A sinω d t-φ)-{2J1(B)sin(1·ω m t)+2J3(B)sin(3·ω m t)+…}sin(A sinω d t-φ)] (10)

[0204] Where J0(B), J1(B), J2(B), ... are Bessel coefficients.

[0205] When deformed as described above, it is theoretically possible to extract the frequency band corresponding to a specific number using a bandpass filter.

[0206] Therefore, in the aforementioned preprocessing unit 53, based on this theory, the received light signal is preprocessed according to the following process.

[0207] First, the light-receiving signal output from the aforementioned ADC 532 is split into two signals, a first signal S1 and a second signal S2, at branch JP1. The first signal S1 passes through a first bandpass filter 534. The center angular frequency of the first bandpass filter 534 is set to ω. m Therefore, the first signal S1 after passing through the first bandpass filter 534 is represented by the following formula.

[0208] I pass1 =J1(B){-cos(ω m t+Asinω d t-φ)+cos(ω m tA sinω d t+φ)}

[0209] =-2J1(B)sin(ω) mt)sin(A sinω d t-φ) (11)

[0210] On the other hand, the second signal S2 passes through the second bandpass filter 535. The center angular frequency of the second bandpass filter 535 is set to a value different from the center angular frequency of the first bandpass filter 534. Here, as an example, the center angular frequency of the second bandpass filter 535 is set to 2ω. m Therefore, the second signal S2 after passing through the second bandpass filter 535 is represented by the following formula.

[0211]

[0212] The reference signal Ss is multiplied by the second signal S2 after passing through the second bandpass filter 535 using multiplier 538. The second signal S2 after passing through multiplier 538 is expressed by the following formula.

[0213]

[0214] The second signal S2, after passing through multiplier 538, passes through third bandpass filter 539. The center angular frequency of third bandpass filter 539 is set to the same value as the center angular frequency of first bandpass filter 534. Here, as an example, the center angular frequency of third bandpass filter 539 is set to ω. m Therefore, the second signal S2 after passing through the third bandpass filter 539 is represented by the following formula.

[0215]

[0216] Subsequently, the phase of the first signal S1 represented by the above equation (11) is adjusted by the first delay adjuster 536, and the amplitude is adjusted by the first AGC 540.

[0217] In addition, the amplitude of the second signal S2, represented by the above formula (14), is also adjusted by the second AGC541 so that the amplitude of the second signal S2 is consistent with the amplitude of the first signal S1.

[0218] Then, the first signal S1 and the second signal S2 are added by adder 542. The result of the addition is represented by the following equation (15).

[0219] I 53 =cos(ω m t+A sinω d t-φ) (15)

[0220] As in equation (15) above, by performing an addition operation, unwanted items can be eliminated and desired items can be extracted. The result is input to the demodulation processing unit 55.

[0221] 1.2.3. Composition of the demodulation processing unit

[0222] The demodulation processing unit 55 performs demodulation processing on the sampled signal originating from the object to be measured 14, which is output from the preprocessing unit 53. There are no particular limitations on the demodulation processing method; a well-known method such as quadrature detection can be cited. Quadrature detection is a method of demodulation processing that involves mixing mutually orthogonal signals from the input signal from the outside.

[0223] Figure 1 The demodulation processing unit 55 shown is a digital circuit that includes a multiplier 551, a multiplier 552, a phase shifter 553, a first low-pass filter 555, a second low-pass filter 556, a divider 557, an arctangent arithmetic unit 558, and an output circuit 559.

[0224] 1.2.4. Demodulation processing in the demodulation processing unit

[0225] In the demodulation process, firstly, branch JP2 splits the signal output from preprocessing unit 53 into two. In multiplier 551, one of the split signals is multiplied by the coefficient of performance (cos(ω)) output from oscillation circuit 54. m The reference signal Ss is represented by t). For the other segmented signal, in multiplier 552, it is multiplied by the reference signal Ss output from oscillator circuit 54, whose phase is shifted by -90° by phase shifter 553, and is represented by -sin(ωt). m The signal represented by t). The reference signal Ss and the signal whose phase is shifted by the reference signal Ss are signals whose phases are offset from each other by 90°.

[0226] The signal passing through multiplier 551 passes through the first low-pass filter 555 and is then input as signal x to divider 557. The signal passing through multiplier 552 passes through the second low-pass filter 556 and is then input as signal y to divider 557. Dividing signal y by signal x is performed in divider 557, and the output y / x is passed through arctangent operator 558 to calculate the output atan(y / x).

[0227] Then, the phase is determined by passing the output atan(y / x) through the output circuit 559. As information derived from the object being measured 14, phase connection is performed in the output circuit 559 when there is a 2π phase jump between adjacent points through phase expansion processing. Based on the phase information output from the demodulation processing unit 55, the displacement of the object being measured 14 can be calculated. Thus, a displacement meter is realized. Furthermore, the velocity can be determined from the displacement. Thus, a speed meter is realized.

[0228] The circuit configuration of the demodulation processing unit 55 has been described above, but the circuit configuration of the digital circuit described above is just an example and is not limited thereto. For example, the configuration of the preprocessing unit 53 is not limited to the configuration described above. In addition, the demodulation processing unit 55 is not limited to a digital circuit, but may also be an analog circuit. The analog circuit may also include an F / V converter circuit and a Δ∑ counter circuit.

[0229] Furthermore, the circuit configuration of the demodulation processing unit 55 described above can also obtain frequency information from the object being measured 14. Based on the frequency information, the speed of the object being measured 14 can be calculated.

[0230] 1.3. Suppression of backlight by blocking elements

[0231] Next, the suppression of backlight by the blocking element 17 will be explained.

[0232] The emitted light L1 from laser source 2 diffuses due to light diffraction. Specifically, from the light path R... LD The optical path R of the emitted light L1 from the laser source 2 is at a distance x LD At the location, the diffusion radiation angle θ is represented by the following equation (16).

[0233] R = R LD +θx LD (16)

[0234] In the above equation (16), the second term is the diffraction term. The diffraction phenomenon is generally represented by the following equation (16-1).

[0235] R LD sinθ=mλ (16-1)

[0236] Since the diffraction terms of higher orders after the second order are sufficiently small, they are not considered. In this case, m can be set to 1. In addition, the diffusion radiation angle θ is generally small, so θ << 1. Therefore, the above equation (16-1) can be transformed into the following equation (16-2).

[0237]

[0238] In this way, the aforementioned equation (16) can be transformed into the following equation (16-3).

[0239]

[0240] Based on the above formula (16-3), the optical path R of the outgoing light L1 emitted from the laser source 2 when it enters the collimating lens 3 is calculated.

[0241] Figure 13 It shows from Figure 2The diagram shows the light trail of the emitted light L1 from the laser source 2 and the light trail of the reference light L2 generated by the reflection of the emitted light L1 by the optical modulator 12 as the return light L5 to the laser source 2. It should be noted that... Figure 13 For clarity, the diagram shows the straightened optical path after its mid-bend. Additionally, the L5 backlight includes... Figure 13 In addition to the light originating from the reference light L2, the light source shown may also include light originating from the object light L3, but this is not illustrated. Furthermore, the return light L5 may consist solely of light originating from the object light L3.

[0242] exist Figure 13 In this design, the center of the collimating lens 3 is set as the origin O (reference position), and the distance between the origin O and the optical modulator 12 is set as L. It should be noted that when the collimating lens 3 is omitted, the position where the collimated light is generated is set as the origin O (reference position). For example, in the case of a gas laser such as a He-Ne laser, since the collimated light exits from the exit point, the exit point becomes the origin. Furthermore, the optical path of the reflected light L5 reaching the collimating lens 3 is set as R′.

[0243] Thus, the optical path R′ of the reflected light L5 is represented by the following formula (16-4).

[0244]

[0245] exist Figure 13 In the optical system 50 shown, the intensity of the reflected light L5 reaching the laser source 2 is suppressed by providing a blocking element 17. The principle of this system will be explained below.

[0246] The blocking element 17 is disposed between the collimating lens 3 and the polarizing beam splitter 4. Therefore, if the diameter of the opening 172 of the blocking element 17 is made smaller... If the optical path R′ of the return light L5 is smaller than that of the return light L5, the light intensity of the return light L5 can be reduced.

[0247] The reflected light L5 is the cause of instability in the laser oscillation in laser source 2. Therefore, if the intensity of the reflected light L5 can be reduced, the laser oscillation can be stabilized. It should be noted that when opening 172 is not a perfect circle, the diameter of opening 172... It is the diameter of the circle inscribed within the opening 172.

[0248] Self-mixing in laser source 2 is related to the instability of laser oscillations caused by the backlight L5. Self-mixing is quantified by an index M, which is the product of the "mixing coefficient" and the "amount of backlight L5". The mixing coefficient is proportional to the reciprocal of the resonator length of laser source 2. Therefore, self-mixing is more easily salient in semiconductor laser elements with short resonator lengths when the amount of backlight L5 increases. If self-mixing is suppressed in semiconductor laser elements, it is considered that self-mixing is suppressed in most types of light sources.

[0249] Here, the inventors have discovered that, in order to suppress self-mixing in the laser source 2, the index M needs to satisfy M < 10. -6 This is equivalent to satisfying OD6 when the blocking capability of the blocking element 17 is expressed as optical density (OD value). Therefore, if the blocking element 17 has a blocking capability that satisfies OD6, laser oscillation stabilization can be achieved.

[0250] Based on this, the light intensity P0 of the emitted light L1 and the light intensity P of the returned light L5 that is not blocked by the blocking element 17 are also considered. r As long as the relationship in equation (17) is satisfied, it is acceptable.

[0251]

[0252] Here, the light intensity of the return light L5 that is about to be incident on the blocking element 17 is set as P′r. The light intensity P′r of the return light L5 is expressed by the following formula (18). It should be noted that the following formula (18) is an example when the light intensity distribution of the outgoing light L1 is a Gaussian distribution or a distribution based on a Gaussian distribution.

[0253] P′ r =P1×P2×P3 (18)

[0254]

[0255]

[0256]

[0257]

[0258] P3 = 1 - cos 2 (2Δψ) (18-3)

[0259] In equation (18-1) above, P is the peak light intensity of the emitted light L1, r is the radial position of the emitted light L1 from its central axis, and w is the light intensity of the emitted light L1, which is 1 / e of the peak light intensity. 2The position is the radial distance from the central axis of the emitted light L1. It should be noted that, in the case of emitted light L1, since θ << 1, it can be θ = λ / r. Therefore, w is expressed as in equation (18-1-1) above. Thus, equation (18-1) above can be modified as in equation (18-1-2) above. It should be noted that in equation (18-2) above, Refl... M It is the light reflectance on the light modulator 12, Refl S It measures the light reflectance on object 14. In addition, in the above formula (18-3), Δψ is the error of the setting angle of the half-wavelength plate, which is virtually formed by the two wavelength plates 6 and 8.

[0260] P1, expressed in equation (18-1), represents the light intensity of the emitted light L1 through the opening 172 of the blocking element 17. P2, expressed in equation (18-2), represents the reflectivity of the light modulator 12 and the reflectivity of the object being measured 14. P3, expressed in equation (18-3), represents the intensity of the light returning to the laser source 2 via the polarization beam splitter 4 when unexpected polarized light is generated due to the allowable angular error of the half-wave plate.

[0261] Based on the above formula (18), when the outgoing light L1 and the return light L5 are coaxial, the light intensity Pr of the return light L5 that is not blocked by the blocking element 17 and passes through the opening 172 is expressed by the following formula (19).

[0262]

[0263] In equation (19) above, x and y are the positions along two mutually orthogonal axes in the cross section of the return light L5. Furthermore, when the intensity distribution of the outgoing light L1 is Gaussian, w = 2σ when the standard deviation of the intensity distribution is set to σ.

[0264] Therefore, in order for the light intensity Pr calculated by the above equation (19) to satisfy the aforementioned equation (17), it is only necessary to select the diameter of the opening 172 of the blocking element 17. Thus, a laser interferometer 1 is achieved, enabling the stabilization of laser oscillations.

[0265] Specifically, in this embodiment, the diameter of the opening 172 As long as the relationship in equation (20) is satisfied, it is acceptable.

[0266] 0.10≤φ pin ≤10.0 (20)

[0267] When the diameter of the opening is 172 When within this range, the return light L5 can be blocked by the blocking element 17. As a result, the intensity of the return light L5 reaching the laser source 2 can be suppressed, and the laser oscillation can be prevented from becoming unstable.

[0268] 1.3.1. First Calculation Example

[0269] As an example of the light intensity Pr calculated by the above equation (19) satisfying the aforementioned equation (17), a first calculation example is shown. The parameters and calculation results of the first calculation example are shown in Table 1.

[0270] [Table 1]

[0271]

[0272] In the first calculation example, as shown in Table 1, the diameter of the opening 172 of the blocking element 17 is... Set the distance x between the collimating lens 3 and the laser source 2 to 0.1mm. LD Setting it to 4.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 1.0deg, thus P r The result of calculating / P0 is less than 1×10 -6 Therefore, in the first calculation example, the reflected light L5 incident on the laser source 2 can be suppressed to a degree that the laser oscillation will not become unstable.

[0273] It should be noted that if the error Δψ of the setting angle of the 1 / 2 wavelength plate is preferably 0.5 degrees or less, more preferably 0.2 degrees or less, it is allowed as an assembly error. Therefore, if the error Δψ is the above value, a laser interferometer 1 with excellent manufacturing ease can be realized.

[0274] 1.3.2. Calculation Examples 2 to 6

[0275] As examples of light intensity Pr calculated using equation (19) satisfying equation (17) above, the second to sixth calculation examples are shown. The parameters and calculation results of the first to sixth calculation examples are shown in Table 2.

[0276] [Table 2]

[0277]

[0278] In the second calculation example, as shown in Table 2, the diameter of the opening 172 of the blocking element 17 is... Set the distance x between the collimating lens 3 and the laser source 2 to 0.4mm. LD Setting it to 4.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0279] In the third calculation example, as shown in Table 2, the diameter of the opening 172 of the blocking element 17 is... Set the distance x between the collimating lens 3 and the laser source 2 to 2.0mm. LD Setting it to 15.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0280] In the fourth calculation example, as shown in Table 2, the diameter of the opening 172 of the blocking element 17 is... Set the distance x between the collimating lens 3 and the laser source 2 to 2.0mm. LD Setting it to 45.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 1.0deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0281] In the fifth calculation example, as shown in Table 2, the diameter of the opening 172 of the blocking element 17 is... Set the distance x between the collimating lens 3 and the laser source 2 to 6.0mm. LD Setting it to 45.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0282] In the sixth calculation example, as shown in Table 2, the diameter of the opening 172 of the blocking element 17 is... Set the distance x between the collimating lens 3 and the laser source 2 to 10.0mm. LD Setting it to 70.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0283] Therefore, in the second to sixth calculation examples, by satisfying It can suppress the reflected light L5 incident on the laser source 2 to a degree that the laser oscillation will not become unstable.

[0284] 1.4. Effects of the first implementation method

[0285] As described above, the laser interferometer 1 according to this embodiment includes a laser source 2, a blocking element 17, an optical modulator 12, and a light-receiving element 10. The laser source 2 emits outgoing light L1 (laser). The blocking element 17 has an opening 172 for the outgoing light L1 to pass through. The optical modulator 12 modulates the outgoing light L1 into a reference light L2 with a different frequency. The light-receiving element 10 receives the object light L3 generated by the reflection of the outgoing light L1 from the object to be measured 14 and the reference light L2, and outputs a light-receiving signal. Furthermore, when the diameter of the opening 172 is set to... At that time, laser interferometer 1 satisfies

[0286] Based on this configuration, the diameter is appropriately selected within the aforementioned range according to other parameters. The intensity of the reflected light L5 incident on the laser source 2 can be sufficiently suppressed. This allows for the stabilization of laser oscillations in the laser source 2. Consequently, due to the stable quality of the emitted light L1, the decrease in accuracy of demodulating the sampled signal from the received light signal in the demodulation circuit 52 can be suppressed.

[0287] Furthermore, in this embodiment, the emitted light L1 and the reflected light L5 are coaxial. Therefore, compared to the case where they are non-coaxial as described later, the adjustment of the laser interferometer 1 is easier, and the working distance of the laser interferometer 1, i.e., the distance to the object 14 that the laser interferometer 1 can measure, can be relatively longer. Thus, according to this embodiment, a laser interferometer 1 with good measurement accuracy of the displacement and velocity of the object 14 and excellent operability can be achieved.

[0288] It should be noted that the diameter of the opening is 172. Preferred satisfaction More preferably satisfied Further optimization to meet

[0289] When the diameter of the opening is 172 When the light intensity is below the lower limit, the intensity of the emitted light L1 through the opening 172 decreases drastically. Consequently, the signal-to-noise ratio (S / N) in the received signal decreases, and the measurement accuracy of the displacement and velocity of the object 14 decreases. On the other hand, when the diameter of the opening 172... When the upper limit is exceeded, the light intensity that can be reduced by the blocking element 17 becomes smaller. Therefore, it is not possible to sufficiently reduce the light intensity of the reflected light L5 incident on the laser source 2.

[0290] In addition, although the emitted light L1 (laser) incident on the light modulator 12 can also be non-collimated light, it is collimated light in this embodiment.

[0291] Therefore, it is possible to suppress the enlargement of the optical modulator 12 and the polarization beam splitter 4, and to achieve miniaturization and weight reduction of the laser interferometer 1. In addition, suppressing the expansion of the optical path of the emitted light L1 makes it easier to improve the S / N ratio in the received light signal.

[0292] Furthermore, although the light intensity distribution on the cross-section of the collimated light can be any distribution, a Gaussian distribution is preferred. Additionally, when the standard deviation of the Gaussian distribution is set to σ [mm], the diameter of the opening 172... Preferred satisfaction In this case, approximately 10% to 99% of the intensity of the emitted light L1 from the laser source 2 passes through the opening 172. Additionally, the diameter of the opening 172... More preferably satisfied In this case, approximately 40% to 99% of the intensity of the emitted light L1 from the laser source 2 passes through the opening 172. The diameter of the opening 172... Setting the light intensity to this range ensures the necessary and sufficient light intensity for the emitted light L1 passing through the opening 172. As a result, it is possible to suppress the decrease in the S / N ratio in the received light signal and suppress the decrease in the measurement accuracy of the displacement and velocity of the object being measured 14.

[0293] Additionally, the distance x between the collimating lens 3 and the laser source 2 LD This is equivalent to the focal length of collimating lens 3. Distance x LD Preferably, the diameter is 1.5 mm or more and 70.0 mm or less, more preferably 2.5 mm or more and 45.0 mm or less. This is especially true for the diameter of the opening 172. When the distance is 2mm or more, the distance x LD Preferably, the diameter is 15.0 mm or more and 45.0 mm or less. This allows for a further expansion of the permissible range of error Δψ.

[0294] It should be noted that the distance L between the collimating lens 3 and the light modulator 12 is preferably set to 5.0 mm or more and 200 mm or less, and more preferably 10.0 mm or more and 100 mm or less. This allows for both minimizing the size of the optical system 50 and ensuring a sufficient working distance.

[0295] In addition, the distance L between the collimating lens 3 and the blocking element 17 pin Preferably, the diameter is 0.5 mm or more and 15.0 mm or less, more preferably 1.0 mm or more and 10.0 mm or less. This allows the optical system 50 to be enlarged while enabling the blocking element 17 to function effectively.

[0296] 2. Second Implementation Method

[0297] Next, the laser interferometer involved in the second embodiment will be described.

[0298] Figure 14 This is a simplified configuration diagram showing the sensor head of the laser interferometer 1 according to the second embodiment. Figure 15 It shows from Figure 14 The diagram shows the light trail of the emitted light L1 from the laser source 2 and the light trail of the reference light L2 generated by the reflection of the emitted light L1 by the optical modulator 12 as the return light L5 to the laser source 2.

[0299] The second embodiment will now be described, but the description will focus on the differences from the first embodiment, while identical details will be omitted. It should be noted that in the figures, the same reference numerals are used to label the same components as in the first embodiment.

[0300] 2.1. Suppression of backlighting through blocking elements and optical axis deviation

[0301] In the first embodiment described above, the emitted light L1 and the returned light L5 are coaxial. In contrast, in the second embodiment, the emitted light L1 and the returned light L5 are not coaxial. Specifically, as... Figure 14 and Figure 15 As shown, the optical modulator 12 is tilted such that the optical axis of the reference light L2 generated by the optical modulator 12 is deviated from the optical axis of the reflected light L1a (outgoing light L1) incident on the optical modulator 12. Therefore, even if a portion of the reference light L2 is reflected again by the polarizing beam splitter 4 to generate a return light L5, the optical axis of the collimated outgoing light L1 (first optical axis A1) and the optical axis of the return light L5 originating from the reference light L2 (second optical axis A2) are non-coaxial. As a result, the return light L5 can be suppressed from incident on the laser source 2. In this specification, the misalignment of the first optical axis A1 and the second optical axis A2 is referred to as "optical axis misalignment." The first optical axis A1 is the optical axis of the outgoing light L1, and the second optical axis A2 is the optical axis of both the reference light L2 and the return light L5 originating from the reference light L2. It should be noted that the direction of optical axis misalignment, besides being as shown... Figure 2 The direction of the optical system 50 shown can be outside the plane extending from the plane, or it can be in a direction intersecting the plane.

[0302] As a result of the optical axis deviation, a deviation occurs between the first optical axis A1 and the second optical axis A2 at the position of the collimating lens 3. Figure 15 In this context, the deviation between the first optical axis A1 and the second optical axis A2 at collimating lens 3 is set as Δy [mm]. Additionally, in... Figure 15In this context, the angle between the first optical axis A1 and the second optical axis A2 is set as the deviation angle θ′. Furthermore, the distance between the center of the collimating lens 3 and the light modulator 12 is set as L. Thus, the deviation amplitude Δy is represented by the following equation (21).

[0303] Δy=L tanθ′ (21)

[0304] On the other hand, the deviation angle θ′ is usually θ′ << 1. Therefore, the above equation (21) can be transformed into the following equation (22).

[0305]

[0306] When considering the deviation magnitude Δy obtained in this way, equation (19) in the first embodiment is replaced as follows (23).

[0307]

[0308]

[0309] In the above equation (23-1), R pin It is the optical path of the reflected light L5 on the blocking element 17, L pin It is the distance between the center of the collimating lens 3 and the center of the blocking element 17.

[0310] Therefore, in order for the light intensity Pr calculated by the above equation (23) to satisfy the aforementioned equation (17), it is only necessary to select the diameter of the opening 172 of the blocking element 17. The deviation amplitude Δy is sufficient. Thus, the laser interferometer 1 can achieve the stabilization of laser oscillation.

[0311] Among them, regarding the diameter of the opening 172 of the blocking element 17 It is the same as the first implementation method.

[0312] On the other hand, the deviation magnitude Δy[mm] preferably satisfies the relationship of the following equation (24).

[0313] 0.10≤Δy≤10.0 (24) When the deviation amplitude Δy is within this range, most of the reflected light L5 can be blocked by the blocking element 17. As a result, the intensity of the reflected light L5 reaching the laser source 2 can be suppressed, and the laser oscillation can be prevented from becoming unstable.

[0314] 2.1.1. Seventh Calculation Example

[0315] As an example of the light intensity Pr calculated by the above equation (23) satisfying the aforementioned equation (17), the seventh calculation example is shown.

[0316] The parameters and calculation results for the seventh calculation example are shown in Table 3.

[0317] [Table 3]

[0318]

[0319] In the seventh calculation example, as shown in Table 3, the diameter of the opening 172 of the blocking element 17 is... Set the deviation amplitude Δy of the reflected light L5 at the collimating lens 3 to 0.50mm (≈0.7σ), and set the distance x between the collimating lens 3 and the laser source 2 to 0.10mm. LD Setting it to 4.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 Therefore, in the seventh calculation example, the reflected light L5 incident on the laser source 2 can be suppressed to a degree that the laser oscillation will not become unstable.

[0320] 2.1.2. Calculation Examples 8 to 16

[0321] As an example of the light intensity Pr calculated by the above equation (23) satisfying the aforementioned equation (17), calculation examples eight through sixteen are shown. The parameters and calculation results of calculation examples seven through sixteen are shown in Table 4.

[0322] [Table 4]

[0323]

[0324] In the eighth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 2.10mm (≈3.0σ), and the distance x between the collimating lens 3 and the laser source 2 is set to 1.80mm. LD Setting it to 4.0mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0325] Furthermore, in the seventh and eighth calculation examples, it was confirmed that, in particular, by adjusting the diameter of opening 172... Set as Set the deviation Δy to 0.10mm ≤ Δy ≤ 10.0mm, thus comparing it with P. r / P0 satisfies the relationship of the aforementioned equation (17).

[0326] In the ninth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... Set the deviation amplitude Δy of the reflected light L5 at the collimating lens 3 to 0.70mm (≈1.0σ), and set the distance x between the collimating lens 3 and the laser source 2 to 0.75mm. LD Setting it to 4.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 1.0deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0327] In the tenth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 2.10mm (≈3.0σ), and the distance x between the collimating lens 3 and the laser source 2 is set to 2.30mm. LD Setting it to 4.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 1.0deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0328] Furthermore, in the ninth and tenth calculation examples, it was confirmed that, in particular, by adjusting the diameter of opening 172... Set as The deviation range Δy is set to 0.70mm ≤ Δy ≤ 10.0mm, thus ensuring that even if the allowable error Δψ reaches 1.0deg, it is still better than P. r / P0 also satisfies the relationship of the aforementioned equation (17).

[0329] In the eleventh calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 1.60mm (≈3.0σ), and the distance x between the collimating lens 3 and the laser source 2 is set to 1.40mm. LD Setting it to 3.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0330] In the twelfth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... Set the deviation amplitude Δy of the reflected light L5 at the collimating lens 3 to 0.40mm (≈0.7σ), and set the distance x between the collimating lens 3 and the laser source 2 to 0.10mm. LD Setting it to 3.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0331] Furthermore, in the eleventh and twelfth calculation examples, it was confirmed that, in particular, by adjusting the diameter of opening 172... Set as Set the deviation Δy to 0.70mm ≤ Δy ≤ 10.0mm, thus ensuring that the distance L and the distance L pin Shorter, than P r / P0 also satisfies the relationship of the aforementioned equation (17). As a result, the volume of the sensor head 51 of the laser interferometer 1 can be reduced to, for example, less than 10cc. As a result, the laser interferometer 1 can be miniaturized in particular.

[0332] In the thirteenth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 0.53mm (≈1.0σ), and the distance x between the collimating lens 3 and the laser source 2 is set to 0.50mm. LD Setting it to 3.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 1.0deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0333] In the fourteenth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 1.90mm (≈3.0σ), and the distance x between the collimating lens 3 and the laser source 2 is set to 2.10mm. LD Setting it to 3.0mm suppresses the error Δψ of the half-wavelength plate's setting angle to 1.0deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0334] Furthermore, in the thirteenth and fourteenth calculation examples, in particular, by measuring the diameter of opening 172... Set as By setting the deviation amplitude Δy to 0.50mm≤Δy≤10.0mm, even if the volume of the sensor head 51 is reduced to, for example, less than 10cc, the error Δψ can be allowed to be 1.0deg.

[0335] In the fifteenth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 6.00mm, and the distance x between the collimating lens 3 and the laser source 2 is set to 2.00mm. LDSetting it to 40mm, the error Δψ of the half-wavelength plate's setting angle is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0336] In the sixteenth calculation example, as shown in Table 4, the diameter of the opening 172 of the blocking element 17 is... The deviation amplitude Δy of the reflected light L5 at the collimating lens 3 is set to 10.0mm, and the distance x between the collimating lens 3 and the laser source 2 is set to 3.50mm. LD By setting it to 65mm, the error Δψ in the setting angle of the 1 / 2 wavelength plate is suppressed to 0.2deg, thus P r The result of calculating / P0 is less than 1×10 -6 .

[0337] Therefore, in the seventh to sixteenth calculation examples, by satisfying This suppresses the reflected light L5 incident on the laser source 2 to a level where the laser oscillation will not become unstable.

[0338] 2.2. Effects of the second implementation method

[0339] As described above, in the laser interferometer 1 according to this embodiment, the optical axis of the outgoing light L1, which serves as collimated light, is designated as the "first optical axis A1". When the reference light L2 or the object light L3 is generated and returns to the laser source 2 via the return light L5, the optical axis of the return light L5 is designated as the "second optical axis A2". Furthermore, the position where the collimated light is generated, i.e., the center of the collimating lens 3, is designated as the reference position, and the deviation between the first optical axis A1 and the second optical axis A2 at the reference position is designated as Δy [mm]. In the laser interferometer 1 according to this embodiment, the first optical axis A1 and the second optical axis A2 are deviated in such a manner that 0.10 ≤ Δy ≤ 10.0.

[0340] With this configuration, the first optical axis A1 of the emitted light L1 and the second optical axis A2 of the returned light L5 are non-coaxial. Consequently, the second optical axis A2 of the returned light L5 is offset from the center of the opening 172 of the blocking element 17. As a result, even without reducing the diameter of the opening 172... It can also suppress the return light L5 from incident on the laser source 2. Therefore, according to this embodiment, it is possible to improve the signal-to-noise ratio in the received signal while stabilizing the laser oscillation in the laser source 2. As a result, the quality of the emitted light L1 is stable, and the accuracy of demodulating the sampled signal from the received signal in the demodulation circuit 52 can be improved. As a result, the measurement accuracy of the displacement and velocity of the object 14 can be improved.

[0341] Furthermore, if the deviation amplitude Δy is within the aforementioned range, the error Δψ of the setting angle of the 1 / 2 wavelength plate can be easily suppressed within the range allowed as an assembly error. Therefore, a laser interferometer 1 with excellent manufacturing ease can be realized.

[0342] It should be noted that the deviation amplitude Δy preferably satisfies 0.50≤Δy≤10.0, more preferably 2.10≤Δy≤10.0, and even more preferably 2.30≤Δy≤10.0. Furthermore, when considering the size of the sensor head 51, the upper limit of the deviation amplitude Δy is more preferably 6.00 or less, and even more preferably 3.00 or less.

[0343] When the deviation Δy is below the aforementioned lower limit, the intensity of the reflected light L5 incident on the laser source 2 increases, and the allowable range of the error Δψ narrows, potentially reducing the ease of manufacturing the optical system 50. On the other hand, when the deviation Δy exceeds the aforementioned upper limit, it is necessary to increase the size of the polarization beam splitter 4, thus making it difficult to miniaturize the sensor head 51.

[0344] Furthermore, the laser interferometer 1 according to this embodiment includes a collimating lens 3. The collimating lens 3 is disposed between the laser source 2 and the blocking element 17. In addition, the collimating lens 3 makes the outgoing light L1 (laser) emitted from the laser source 2 parallel to generate collimated light.

[0345] With this configuration, collimated light can be generated even when using a semiconductor laser element as the laser source 2. This allows for the reduction of the size of the polarization beam splitter 4, and enables the miniaturization and weight reduction of the laser interferometer 1. Furthermore, it facilitates the suppression of the expansion of the emitted light path L1 and improves the signal-to-noise ratio (S / N) in the received light signal.

[0346] 3. First to fifth variations of the laser interferometer

[0347] Next, the laser interferometers involved in the first to fifth variations will be explained.

[0348] Figure 16 This is a simplified structural diagram showing the mounting structure of the optical system of the laser interferometer involved in the first modified example. Figure 17 This is a simplified structural diagram showing the mounting structure of the optical system of the laser interferometer involved in the second variation. Figure 18 This is a simplified configuration diagram showing the mounting structure of the optical system of the laser interferometer involved in the third variation. Figure 19 This is a simplified configuration diagram showing the mounting structure of the optical system of the laser interferometer involved in the fourth variation.

[0349] The first to fourth variations will be described below, but the description will focus on the differences from the aforementioned embodiments, while identical details will be omitted. It should be noted that in... Figures 16 to 19 In the drawings, the same reference numerals are used to indicate the same components as in the aforementioned embodiments.

[0350] Figure 16 The optical system 50D of the laser interferometer 1 shown includes a substrate 39. A laser source 2, an optical modulator 12, and a light-receiving element 10 are respectively mounted on this substrate 39. Furthermore, in Figure 16 On the substrate 39 shown, the light receiving element 10, the laser source 2, and the light modulator 12 are arranged sequentially along a direction orthogonal to the light path 22.

[0351] in addition, Figure 16 The optical system 50D shown includes prisms 40 and 42. Prism 40 is disposed on the optical path 24 between the light-receiving element 10 and the analyzer 9. Prism 42 is disposed on the optical path 20 between the light modulator 12 and the quarter-wave plate 8.

[0352] and, Figure 16 The optical system 50D shown includes a collimating lens 44. The collimating lens 44 is disposed on the optical path 18 between the laser source 2 and the polarizing beam splitter 4.

[0353] In the first variation example as described above, the same effect as the aforementioned implementation method can also be obtained.

[0354] Figure 17 The optical system 50E of the laser interferometer 1 shown is similar to that of the laser interferometer 1, except for the different configuration of components, etc. Figure 16 The optical system shown is the same as that of the 50D.

[0355] exist Figure 17 On the substrate 39 shown, the laser source 2, the light receiving element 10, and the light modulator 12 are arranged sequentially along a direction orthogonal to the optical path 22. The prism 40 is disposed on the optical path 18, and the prism 42 is disposed on the optical path 20.

[0356] In a second variation like the one described above, the same effect as the aforementioned implementation can also be obtained.

[0357] Figure 18 The optical system 50F of the laser interferometer 1 shown is different from the laser receiver 10 except for the different configuration of components and the different laser light received by the light-receiving element. Figure 17 The optical system shown, 50E, is the same.

[0358] exist Figure 18On the substrate 39 shown, the laser source 2, the light modulator 12, and the light receiving element 10 are arranged sequentially along a direction orthogonal to the optical path 22. The prism 42 is disposed on the optical path 24.

[0359] The emitted light L1 from the laser source 2 is split into two by the polarizing beam splitter 4 after passing through the prism 40. The emitted light L1 reflected by the polarizing beam splitter 4 passes through the quarter-wave plate 6 and is incident on the active measurement object 14. The emitted light L1 undergoes a Doppler frequency shift on the measurement object 14 and is reflected as object light L3. Object light L3 passes through the quarter-wave plate 6, the polarizing beam splitter 4, and the quarter-wave plate 8, and is incident on the optical modulator 12. Object light L3 undergoes a frequency shift on the optical modulator 12 and is reflected as object reference light L4. Object reference light L4 passes through the quarter-wave plate 8, the polarizing beam splitter 4, the prism 42, and the analyzer 9, and is incident on the light receiving element 10.

[0360] On the other hand, the outgoing light L1, which passes through the polarizing beam splitter 4, passes through the prism 42 and the analyzer 9, and is incident on the light receiving element 10.

[0361] Then, the object reference light L4 and the emitted light L1 are incident on the light-receiving element 10 as interference light. The object reference light L4 is a laser beam containing a modulation signal and a sampling signal.

[0362] In addition, in this modified example, the light receiving element 10 receives the interference light between the object reference light L4 and the emitted light L1, and the demodulation circuit 52 demodulates the sampled signal contained in the object reference light L4 based on the reference signal Ss and the modulation signal contained in the object reference light L4.

[0363] In a third variation like the one described above, the same effect as the aforementioned implementation can be obtained.

[0364] Figure 19 The optical system 50G of the laser interferometer 1 shown is similar to the laser interferometer 1 except that the orientation of the light reflecting surface of the polarization beam splitter 4 is different. Figure 18 The optical system shown in 50F is the same.

[0365] The emitted light L1 from the laser source 2 passes through the prism 40 and is split into two by the polarizing beam splitter 4.

[0366] The outgoing light L1, reflected by the polarizing beam splitter 4, passes through the quarter-wave plate 8 and enters the optical modulator 12. The outgoing light L1 undergoes a frequency shift at the optical modulator 12 and is reflected as reference light L2. Reference light L2 passes through the quarter-wave plate 8, the polarizing beam splitter 4, and the quarter-wave plate 6, and enters the active measurement object 14. Reference light L2 undergoes a Doppler frequency shift at the measurement object 14 and is reflected as object reference light L4. Object reference light L4 passes through the quarter-wave plate 6, the polarizing beam splitter 4, the prism 42, and the analyzer 9, and enters the light-receiving element 10.

[0367] On the other hand, the outgoing light L1, which passes through the polarizing beam splitter 4, passes through the prism 42 and the analyzer 9, and is incident on the light receiving element 10.

[0368] Then, the object reference light L4 and the emitted light L1 are incident on the light-receiving element 10 as interference light. The object reference light L4 is a laser beam containing a modulation signal and a sampling signal.

[0369] In addition, in this modified example, the light receiving element 10 receives the interference light between the object reference light L4 and the emitted light L1, and the demodulation circuit 52 demodulates the sampled signal contained in the object reference light L4 based on the reference signal Ss and the modulation signal contained in the object reference light L4.

[0370] In the fourth variation, as described above, the same effect as the aforementioned implementation can be obtained.

[0371] According to the above Figures 16 to 19 The mounting structure shown allows for easy miniaturization of the laser interferometer 1. It should be noted that the component configuration is not limited to the configuration shown in the figure.

[0372] In addition, Figures 16 to 19 In the mounting structure shown, the size of the light-receiving element 10 is, for example, 0.1 mm square, the size of the laser light source 2 is, for example, 0.1 mm square, and the size of the light modulator 12 is, for example, 0.5 to 10 mm square. Furthermore, the size of the substrate 39 on which they are mounted is, for example, 1 to 10 mm square. Thus, it is possible to miniaturize the optical system to the size of this substrate 39.

[0373] The above-described embodiments and variations all possess what is known as a Michelson-type interference optical system. In contrast, Figure 20 The optical system 50H of the laser interferometer 1 shown differs in that it is a Mach-Zehnder type interferometric optical system. This invention can also be applied to laser interferometers with Mach-Zehnder type interferometric optical systems.

[0374] Figure 20This is a simplified structural diagram showing the optical system 50H of the laser interferometer 1 involved in the fifth modification. It should be noted that... Figure 20 The diagram only shows the main optical components, omitting some of them.

[0375] Figure 20 The optical system 50H shown includes a laser source 2, polarizing beam splitters 4a, 4b, and 4c (optical splitters), a quarter-wavelength plate 6, a half-wavelength plate 7, an analyzer 9, an optical modulator 12H, a mirror 41, a light-receiving element 10, and a blocking element 17. In the optical system 50H, the optical modulator 12H is transparent. Therefore, examples of optical modulators 12H include acousto-optic modulators (AOM) and electro-optic modulators (EOM).

[0376] In this fifth variation, as described above, by including the blocking element 17 and tilting the light modulator 12H as needed, it is possible to suppress the backlight L5 from incident on the laser source 2. Therefore, in this fifth variation, the same effect as in the aforementioned embodiment can be obtained.

[0377] The laser interferometer of the present invention has been described above based on the illustrated embodiments. However, the laser interferometer of the present invention is not limited to the aforementioned embodiments, and the configuration of each part can be replaced with any configuration having the same function. Furthermore, other arbitrary components may be added to the laser interferometer involved in the aforementioned embodiments. Additionally, the laser interferometer of the present invention can also combine any two or more of the aforementioned embodiments and their variations.

[0378] In addition to the aforementioned displacement gauges and velocities, the laser interferometer of this invention can also be applied to, for example, vibration meters, inclinometers, and distance meters (length measuring devices). Furthermore, examples of applications of the laser interferometer of this invention include optical comb interferometry, which enables distance measurement, 3D imaging, and beam splitting, and fiber optic gyroscopes, which realize angular velocity sensors and angular acceleration sensors.

Claims

1. A laser interferometer, characterized in that, have: Laser source, emits laser light; A shielding element having an opening for the laser to pass through; An optical modulator modulates the laser light into reference light of different frequencies; and The light-receiving element receives the object light generated by the laser reflected from the object being measured, as well as the reference light, and outputs a light-receiving signal. When the diameter of the opening is set to pin When the laser interferometer satisfies 0.10 ≤ pin ≤10.0, where the diameter of the opening is... pin The unit is mm. The laser light incident on the optical modulator is collimated light. When the optical axis of the collimated light is set as the first optical axis, When the reference light or the object light is generated and returns to the laser source, the optical axis of the returning light is set as the second optical axis. Set the position where the collimated light is generated as the reference position. When the deviation between the first optical axis and the second optical axis at the reference position is set as Δy, The first optical axis and the second optical axis are offset in such a way that 0.10≤Δy≤10.0, wherein the unit of the offset Δy between the first optical axis and the second optical axis at the reference position is mm.

2. The laser interferometer according to claim 1, characterized in that, The light intensity distribution on the cross-section of the collimated light is Gaussian. When the standard deviation of the Gaussian distribution is set to σ, the diameter of the opening... pin Satisfying 0.5σ≤ pin / 2≤3.0σ, where the standard deviation σ of the Gaussian distribution is in mm.

3. The laser interferometer according to claim 1, characterized in that, The laser source is a semiconductor laser element.

4. The laser interferometer according to claim 3, characterized in that, The laser interferometer includes a collimating lens disposed between the laser source and the blocking element. The collimating lens makes the laser emitted from the laser source parallel to generate the collimated light.

5. The laser interferometer according to claim 1, characterized in that, The optical modulator has a vibrating element. The optical modulator uses the vibrating element to modulate the laser.

6. The laser interferometer according to claim 5, characterized in that, The laser interferometer has the following features: The demodulation circuit demodulates the sampled signal originating from the measured object based on the reference signal from the received light signal; and The oscillation circuit outputs the reference signal to the demodulation circuit. The vibrating element is the signal source of the oscillation circuit.

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