laser interferometer

Abstract

The present application provides a laser interferometer, which can realize miniaturization of an optical system and easy alignment. The laser interferometer is characterized by comprising: a laser light source that emits first laser light; a light modulator that includes a vibration element, modulates the first laser light using the vibration element, and generates second laser light that includes a modulation signal; a light receiving element that receives the second laser light and third laser light and outputs a light receiving signal, the third laser light including a sample signal generated by reflection of the first laser light on a measured object; an optical coupler that has a function of branching the first laser light and a function of branching a combined light of the second laser light and the third laser light; a first collimator that parallelizes the first laser light branched by the optical coupler; a second collimator that parallelizes the first laser light branched by the optical coupler; a first optical wiring; a second optical wiring; a third optical wiring; and a fourth optical wiring.

Description

Technical Field

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

[0002] Patent Document 1 discloses a laser vibrator as an apparatus for measuring the vibration velocity of an object. In this laser vibrator, a laser is irradiated onto the object being measured, and the vibration velocity is measured based on the scattered laser light that has undergone a Doppler frequency shift.

[0003] Specifically, the laser vibrator described in Patent Document 1 includes a vibrating element such as a piezoelectric element. The vibrating element shifts the frequency of the laser beam according to its vibration frequency. Additionally, the object being measured also shifts the laser beam frequency according to its vibration state. The frequency-shifted light, received by both the vibrating element and the object being measured, returns as reflected light to a semi-reflecting mirror. In the semi-reflecting mirror, the returned light is reflected and enters a photodetector, while a portion of the laser beam is reflected, reflected again in the mirror, and transmitted through the photodetector as reference light. Furthermore, the photodetector performs optical mixing of the returned light and the reference light, and electrically extracts the beat frequency. Then, a frequency-modulated wave demodulator and a signal processing device detect the vibration of the object being measured as a frequency shift and quantify it.

[0004] The laser vibrator described in Patent Document 1 includes optical elements such as a semiconductor laser that emits a laser beam, a semi-reflective mirror, a polarizing beam splitter, a λ / 4 plate, a reflector, a vibrating element, and a photodetector. The polarizing beam splitter allows light emitted from the laser to pass through and enter the vibrating element, where it is reflected and then directed to the object being measured, and further reflected back into the vibrating element. Additionally, as described above, the semi-reflective mirror reflects the returning light and allows reference light to pass through, both of which are directed to the photodetector.

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-285898

[0006] In the laser vibrator described in Patent Document 1, as mentioned above, various optical elements are optically connected to each other. Therefore, sufficient space is required to accommodate each optical element, making miniaturization of the optical system difficult. Furthermore, high alignment accuracy of the optical elements is required to obtain a high-precision beat frequency. Therefore, alignment is time-consuming and labor-intensive. Additionally, the need for an alignment adjustment mechanism further hinders miniaturization of the optical system from this perspective.

[0007] For the reasons mentioned above, miniaturization of optical systems and simplification of alignment operations have become key issues. Summary of the Invention

[0008] The laser interferometer according to the applicable examples of the present invention is characterized by comprising:

[0009] The laser source emits the first laser beam.

[0010] An optical modulator, comprising a vibrating element, uses the vibrating element to modulate the first laser to generate a second laser containing a modulated signal;

[0011] A light-receiving element receives the second laser and the third laser, and outputs a light-receiving signal, wherein the third laser includes a sampling signal generated by the reflection of the first laser by the object being measured;

[0012] An optical coupler is provided, wherein the first laser, the second laser, and the third laser are incident on the optical coupler, and the optical coupler has the function of splitting the first laser and splitting the combined beam of the second laser and the third laser;

[0013] A first collimator parallelizes the first laser beam that has been bisected by the optical coupler and directs it toward the optical modulator.

[0014] The second collimator parallelizes the first laser beam that has been split off by the optical coupler and directs it toward the object being measured.

[0015] The first optical fiber connects the laser source to the optical coupler, so that the first laser emitted from the laser source enters the optical coupler.

[0016] The second optical fiber connects the light-receiving element to the optical coupler, so that the combined light split by the optical coupler enters the light-receiving element.

[0017] A third optical wiring connection optically connects the first collimator to the optical coupler; and

[0018] The fourth optical fiber connects the second collimator to the optical coupler. Attached Figure Description

[0019] Figure 1 This is a functional block diagram illustrating the laser interferometer according to the first embodiment.

[0020] Figure 2 It means Figure 1 The diagram shows a schematic representation of the sensor head.

[0021] Figure 3 It means Figure 2 A perspective view of a first example of a light modulator.

[0022] Figure 4 This is a top view showing a portion of a second configuration example of an optical modulator.

[0023] Figure 5 This is a top view showing a third configuration example of an optical modulator.

[0024] Figure 6 This indicates that in the incident light K i A conceptual diagram illustrating the generation of multiple diffracted beams when light enters from a direction perpendicular to the surface of the vibrating element.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Figure 10 This is a cross-sectional view showing an optical modulator with a packaged structure.

[0029] Figure 11 This is a circuit diagram showing the configuration of a single-stage inverter oscillation circuit.

[0030] Figure 12 This is an example of a circuit diagram of the LCR equivalent circuit of a vibrating element.

[0031] Figure 13 This is a perspective view showing the sensor head of the laser interferometer according to the first variation of the first embodiment.

[0032] Figure 14 This is a schematic diagram showing the sensor head of the laser interferometer according to the second variation of the first embodiment.

[0033] Figure 15 This is a schematic diagram showing the sensor head of the laser interferometer according to the second embodiment.

[0034] Figure 16 This is a schematic diagram showing the sensor head of the laser interferometer according to the third embodiment.

[0035] Figure 17 This is a schematic diagram showing the sensor head of the laser interferometer according to the fourth embodiment.

[0036] Figure 18 This is a schematic diagram showing the sensor head of the laser interferometer according to the fifth embodiment.

[0037] Figure 19 This is a schematic diagram showing the sensor head of the laser interferometer according to the sixth embodiment.

[0038] Explanation of reference numerals in the attached figures

[0039] 1…Laser interferometer, 1A…Laser interferometer, 1B…Laser interferometer, 1C…Laser interferometer, 1D…Laser interferometer, 1E…Laser interferometer, 1F…Laser interferometer, 1G…Laser interferometer, 2…Laser source, 4…Optical coupler, 5…Optical isolator, 9…Substrate for mounting, 10…Light receiving element, 12…Optical modulator, 14…Object to be measured, 15…Optical path length changing unit, 15G…Optical path length changing unit, 20…Optical path, 21…Collider, 22…Collider, 23…Collider, 30…Vibration element, 30A…Vibration element, 30B…Vibration element, 31…Substrate, 32… 33… Pad, 34… Diffraction grating, 35… Pad, 36… Vibration direction, 37… Mirror, 45… Circuit element, 50… Optical system, 51… Sensor head, 52… Demodulation circuit, 53… Preprocessing section, 54… Oscillation circuit, 55… Demodulation processing section, 59… Main body, 61… Optical fiber, 62… Optical fiber, 63… Optical fiber, 64… Optical fiber, 70… Container, 72… Container body, 74… Cover, 76… Bonding line, 120… Optical modulation oscillator, 150… Optical reflecting surface, 151… First reflecting element, 152… Second reflecting element, 153… Drive section, 154a… Right angle prism Mirror, 154b…Right-angle prism mirror, 155a…Right-angle prism mirror, 155b…Right-angle prism mirror, 156…Substrate, 157…Substrate, 171…Refractive index variable, 172…Input section, 301…First electrode, 302…Second electrode, 303…Diffraction grating mounting section, 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 adjustment 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…Argontangent Operator, 559…Output Circuit, 721…First Recess, 722…Second Recess, 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, K0s …diffraction light, K 1s …diffraction light, K 2s …Diffraction light, K1…Incident light, L1…Outgoing light, L1…Series inductance, L2…Reference light, L3…Object light, L4…Combined 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…Bifurcation, jp2…Bifurcation, ps1…First signal path, ps2…Second signal path, x…Signal x, y…Signal y, β…Angle of incidence, θ B …Brightness angle, θ S …tilt angle. Detailed Implementation

[0040] The laser interferometer of the present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings.

[0041] 1. First Implementation Method

[0042] First, the laser interferometer involved in the first embodiment will be described.

[0043] Figure 1 This is a functional block diagram illustrating the laser interferometer 1 according to the first embodiment.

[0044] Figure 1 The laser interferometer 1 shown has a sensor head 51 and a main body 59. The sensor head 51 includes an optical system 50, a current-to-voltage converter 531, and an oscillation circuit 54. The main body 59 includes a demodulation circuit 52 that receives light signals from the optical system 50.

[0045] 1.1. Sensor Head

[0046] Figure 2 It means Figure 1 The diagram shows a schematic configuration of the sensor head 51.

[0047] 1.1.1. Optical System

[0048] like Figure 2 As shown, the optical system 50 includes a laser source 2, an optical coupler 4, a light receiving element 10, a collimator 21 (first collimator), a frequency shifter type optical modulator 12, a collimator 22 (second collimator), and a measurement object 14.

[0049] An optical fiber 61 (first optical fiber) is provided between the laser source 2 and the optical coupler 4. The optical fiber 61 optically connects the laser source 2 and the optical coupler 4.

[0050] An optical fiber 62 (second optical fiber) is provided between the light-receiving element 10 and the optical coupler 4. The optical fiber 62 optically connects the light-receiving element 10 and the optical coupler 4.

[0051] An optical fiber 63 (third optical fiber) is provided between the collimator 21 and the optical coupler 4. The optical fiber 63 optically connects the collimator 21 and the optical coupler 4.

[0052] An optical fiber 64 (fourth optical fiber) is provided between the collimator 22 and the optical coupler 4. The optical fiber 64 optically connects the collimator 22 and the optical coupler 4.

[0053] In this way, in the optical system 50, optical elements such as the laser source 2, optical coupler 4, light receiving element 10, collimator 21, optical modulator 12, and collimator 22 are optically connected to each other via optical fibers 61-64. In such an optical system 50, fewer connection points for light propagation in free space are required when connecting optical elements. Therefore, alignment can be easily performed, and the need for re-alignment is reduced. Furthermore, while there are limits to the miniaturization of optical elements at connection points requiring alignment, such constraints are not present in the optical system 50, and position adjustment devices required for alignment are not needed. Moreover, the optical fibers 61-64 are flexible, allowing light to propagate even when bent.

[0054] Laser source 2 emits outgoing light L1 (laser). Optical coupler 4 splits outgoing light L1 into two. One of the outgoing light L1s split by optical coupler 4 illuminates optical modulator 12 equipped with vibrating element 30 and is reflected as reference light L2, which contains a modulation signal as a Doppler signal from vibrating element 30. The other outgoing light L1 split by optical coupler 4 illuminates the object to be measured 14 and is reflected as object light L3, which contains a sample signal as a Doppler signal from object to be measured 14. Reference light L2 and object light L3 merge in optical coupler 4 to become a combined light L4, which is then split into two. Light receiving element 10 receives the combined light L4 split by optical coupler 4 and converts it into an electrical signal.

[0055] The sensor head 51 is movable. Movable means possessing the ability to move and having dimensions that allow for a high degree of freedom in setting. The movable sensor head 51 adjusts its position or orientation to allow the emitted light L1 to illuminate the object 14 being measured. Therefore, the sensor head 51 can also be mounted on a position adjustment device such as a goniometer as needed.

[0056] On the other hand, the main body 59 does not need to be movable. Therefore, the main body 59 can be mounted on a storage rack or workbench, for example.

[0057] The following is a further explanation of each part of the optical system 50.

[0058] 1.1.1.1. Laser source

[0059] Laser source 2 is a laser source that emits coherent outgoing light L1. Laser source 2 preferably uses a light source with a linewidth of MHz or less. Specifically, examples include gas lasers such as He-Ne lasers, semiconductor laser elements such as DFB-LD (Distributed Feedback-Laser Diode), FBG-LD (Laser Diode with Fiber Bragg Grating), VCSEL (Vertical Cavity Surface Emitting Laser), and FP-LD (Fabry-Perot Laser Diode).

[0060] The laser source 2 is preferably a semiconductor laser element. This allows for miniaturization and weight reduction of the laser source 2. Consequently, miniaturization of the laser interferometer 1 can be achieved. In particular, since the sensor head 51 housing the optical system 50 in the laser interferometer 1 can be miniaturized and weight reduced, the operability of the laser interferometer 1, such as the degree of freedom in setting the sensor head 51, can be improved.

[0061] 1.1.1.2. Optical Coupler

[0062] Optical coupler 4 is a 2×2 type coupler with four optical input and output terminals. This optical coupler 4 has the functions of splitting the incident outgoing light L1, merging the incident reference light L2 and the object light L3 to obtain the merged light L4, and splitting the merged light L4.

[0063] Examples of optical couplers 4 include fiber optic couplers and optical waveguide couplers.

[0064] In this design, the optical coupler 4 is preferably a fiber optic coupler. The fiber optic coupler is formed, for example, by fusion splicing optical fibers together. Therefore, the fiber optic coupler becomes an integrated structure of the optical coupler 4 (which serves as the fusion splice between the optical fibers) and the optical fibers 61-64 (first optical wiring to fourth optical wiring) extending from the fusion splice. Thus, by using the fiber optic coupler, an optical system 50 with low optical loss can be achieved. Furthermore, since the connection and alignment work between the optical coupler 4 and the optical fibers 61-64 is not required, the assembly of the optical system 50 is also easier. Moreover, the optical coupler 4 and the optical fibers 61-64 can also be independent structures.

[0065] In addition, optical fibers 61 to 64 can be made of glass or plastic, respectively.

[0066] On the other hand, an optical waveguide coupler can be constructed, for example, from an optical waveguide with a bifurcated core. Furthermore, the optical waveguide coupler is easily integrated with optical waveguide wiring extending from the bifurcated core. Therefore, the optical waveguide coupler can also be a structure integrating the optical coupler 4, which is the bifurcated core, with the optical waveguide wiring, which is the first to fourth optical wiring. The optical waveguide wiring can be easily formed in any path within a sheet-like component. Therefore, even when using an optical waveguide coupler that includes optical waveguide wiring, miniaturization, weight reduction, and space saving of the optical system 50 can be easily achieved.

[0067] Materials used to construct optical waveguide couplers include, for example, strong dielectrics, compound semiconductors, glass, and plastics.

[0068] The bifurcation ratio in the optical coupler 4 is not particularly limited, but it is preferably 20:80 or higher and 80:20 or lower, more preferably 40:60 or higher and 60:40 or lower. This prevents extreme bias in the light intensity after bifurcation, thus suppressing the decrease in the signal-to-noise ratio (S / N) of the received signal.

[0069] Furthermore, the laser source 2 and fiber 61, the light-receiving element 10 and fiber 62, the collimator 21 and fiber 63, and the collimator 22 and fiber 64 can be physically and optically connected using an optical adhesive, or they can be optically connected via a small free space. In particular, with the former connection method, after the alignment of the connection points is completed during the manufacturing stage of the optical system 50, no alignment work is required unless the optical elements are repaired or replaced. Therefore, the maintainability of the optical system 50 can be improved. In addition, the former connection method exhibits excellent durability against disturbances such as vibration, shock, and temperature changes.

[0070] 1.1.1.3. Light-receiving element

[0071] The combined light L4, split by the optical coupler 4, enters the light-receiving element 10. The light-receiving element 10 receives the combined light L4 and outputs a light-receiving signal. By demodulating the sampled signal based on the light-receiving signal and using the method described later, the motion, i.e., vibration velocity or displacement, of the object 14 to be measured can be determined. Examples of light-receiving elements 10 include photodiodes.

[0072] 1.1.1.4. Collimator

[0073] Collimator 21 is an optical element (optical component) disposed between optical fiber 63 and optical modulator 12; an aspherical lens can be cited as an example. Collimator 21 parallelizes the outgoing light L1, which is branched by optical coupler 4 and propagates in optical fiber 63, and directs it toward optical modulator 12. The outgoing light L1 propagates in free space and enters optical modulator 12. Meanwhile, reference light L2 generated by optical modulator 12 propagates in free space and enters optical fiber 63 after passing through collimator 21. Furthermore, in this specification, "parallelization" refers not only to making the diverging light completely parallel, but also to correcting the direction of the divergence angle of the diverging light beam. Therefore, for example, the outgoing light L1 or reference light L2 after passing through collimator 21 may not be completely parallel.

[0074] In order to optically connect the collimator 21 to the optical modulator 12, an alignment operation is required. Examples of such alignment operations include adjusting the position of the collimator 21 to parallelize the emitted light L1, directing the emitted light L1 into the optical modulator 12, and adjusting the setting angle of the optical modulator 12 to couple the reference light L2 with the collimator 21.

[0075] Collimator 22 is an optical element (optical component) disposed between optical fiber 64 and the object to be measured 14; an aspherical lens can be cited as an example. Collimator 21 parallelizes the outgoing light L1, which is split by optical coupler 4 and propagates in optical fiber 63, and directs it toward the object to be measured 14. The outgoing light L1 propagates in free space and enters the object to be measured 14. In addition, the object light L3 generated by the object to be measured 14 propagates in free space and enters optical fiber 64 after passing through collimator 22.

[0076] In order to optically connect the collimator 22 with the object to be measured 14, an alignment operation is required. Examples of such alignment operations include adjusting the position of the collimator 22 to parallelize the emitted light L1, inputting the emitted light L1 into the object to be measured 14, and adjusting the setting angle of the sensor head 51 to couple the object light L3 with the collimator 22.

[0077] In addition, collimators 21 and 22 may also contain optical elements other than aspherical lenses.

[0078] 1.1.1.5. Optical Modulator

[0079] Figure 3 It means Figure 2 A perspective view of a first configuration example of the optical modulator 12 shown.

[0080] 1.1.1.5.1. Summary of the First Configuration Example of an Optical Modulator

[0081] The frequency shifter type optical modulator 12 has an optical modulation oscillator 120. Figure 3 The optical modulation oscillator 120 shown has a plate-shaped vibrating element 30 and a substrate 31 supporting the vibrating element 30.

[0082] The vibrating element 30 is made of a material that repeatedly vibrates in a mode that is distorted in a direction along a surface when a voltage is applied. In this configuration example, the vibrating element 30 is an AT-cut quartz oscillator that undergoes thickness shear vibration along the vibration direction 36 in the high-frequency region of the MHz band. A diffraction grating 34 is formed on the surface of the vibrating element 30. The diffraction grating 34 has grooves 32 that hold components intersecting the vibration direction 36, that is, a plurality of straight grooves 32 extending in a direction intersecting the vibration direction 36.

[0083] The substrate 31 has a surface 311 and a back surface 312 that are face-to-back with respect to each other. A vibrating element 30 is disposed on the surface 311. In addition, pads 33 for applying voltage to the vibrating element 30 are provided on the surface 311. On the other hand, pads 35 for applying voltage to the vibrating element 30 are also provided on the back surface 312.

[0084] The size of the substrate 31 is, for example, approximately 0.5 mm or more and 10.0 mm or less on the long side. Additionally, the thickness of the substrate 31 is, for example, approximately 0.10 mm or more and 2.0 mm or less. As an example, the substrate 31 is a square with one side measuring 1.6 mm, and its thickness is 0.35 mm.

[0085] The size of the vibrating element 30 is, for example, about 0.2 mm or more and about 3.0 mm or less on the long side. In addition, the thickness of the vibrating element 30 is, for example, about 0.003 mm or more and about 0.5 mm or less.

[0086] As an example, the vibrating element 30 is a square with one side of 1.0 mm and a thickness of 0.07 mm. In this case, the vibrating element 30 oscillates at a fundamental oscillation frequency of 24 MHz. Furthermore, by changing the thickness of the vibrating element 30 or taking into account harmonics (overtones), the oscillation frequency can be adjusted in the range of 1 MHz to 1 GHz.

[0087] In addition, Figure 3 In this process, the diffraction grating 34 is formed on the entire surface of the vibrating element 30, but it may also be formed on only a portion of it.

[0088] The magnitude of optical modulation 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. In this configuration example, the vibrating element 30 performs thickness shear vibration, but since this vibration is in-plane vibration, optical modulation cannot be performed even if light is incident perpendicularly to the surface of the vibrating element 30. Therefore, in this configuration example, by providing a diffraction grating 34 on the vibrating element 30, optical modulation can be performed according to the principle described later.

[0089] Figure 3 The diffraction grating 34 shown is a blazed diffraction grating. A blazed diffraction grating is a grating with a stepped cross-sectional shape. The straight grooves 32 of the diffraction grating 34 are arranged such that their extension direction is orthogonal to the vibration direction 36.

[0090] 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, ranging from as low as 0.1 μW to about 100 mW. Therefore, the drive signal Sd output from the oscillation circuit 54 can be used to make the vibrating element 30 oscillate without amplification.

[0091] Furthermore, existing optical modulators sometimes require structures to maintain their temperature, making it difficult to reduce their size. Additionally, existing optical modulators consume a lot of power, thus posing a challenge to miniaturization and power saving in laser interferometers. In contrast, in this configuration example, the oscillation element 30 is very small, and the power required for oscillation is also low; therefore, miniaturization and power saving of the laser interferometer 1 are easily achieved.

[0092] 1.1.1.5.2. Methods for forming diffraction gratings

[0093] The method for forming the diffraction grating 34 is not particularly limited. As an example, one method is to fabricate a mold using a mechanical scribing method (scrubbing machine) and then form a groove 32 on the electrode formed on the surface of the vibrating element 30 using nanoimprint lithography. The reason for forming the groove on the electrode is that, in the case of an AT-cut quartz oscillator, high-quality thickness shear vibration can theoretically be generated on the electrode. Furthermore, the formation of the groove 32 is not limited to the electrode and can also be on the surface of a material other than the electrode. Alternatively, exposure-based etching methods, electron beam lithography, focused ion beam (FIB) processing, etc., can be used instead of nanoimprint lithography.

[0094] Alternatively, a diffraction grating can be formed on the chip of an AT-cut quartz oscillator using a photoresist material, and a mirror film composed of a metal film or a multilayer dielectric film can be placed on the diffraction grating. By placing a metal film or a mirror film, the reflectivity of the diffraction grating 34 can be improved.

[0095] Furthermore, a resist film can be formed on the chip or wafer of an AT-cut quartz oscillator. After etching, the resist film is removed, and then a metal film or mirror film is formed on the processed surface. In this case, since the resist material is removed, it is not affected by the moisture absorption of the resist material, thus improving the chemical stability of the diffraction grating 34. Additionally, by setting a highly conductive metal film such as Au or Al, it can also be used as an electrode to drive the oscillation element 30.

[0096] In addition, the diffraction grating 34 can also be formed using techniques such as anodic aluminum oxide (porous aluminum oxide).

[0097] 1.1.1.5.3. Other configuration examples of optical modulators

[0098] The vibrating element 30 is not limited to a quartz oscillator; for example, it can also be a Si oscillator, a surface acoustic wave (SAW) device, a ceramic oscillator, etc.

[0099] Figure 4 This is a top view showing a portion of a second configuration example of the optical modulator 12. Figure 5 This is a top view showing a third configuration example of the optical modulator 12.

[0100] Figure 4 The vibrating element 30A shown is a Si oscillator manufactured from a Si substrate using MEMS technology. MEMS (Micro-Electro-Mechanical Systems) is a micro-electromechanical system.

[0101] The vibrating element 30A includes a first electrode 301 and a second electrode 302 adjacent to each other on the same plane with a gap between them, a diffraction grating mounting portion 303 disposed on the first electrode 301, and a diffraction grating 34 disposed on the diffraction grating mounting portion 303. The first electrode 301 and the second electrode 302 are driven, for example, by electrostatic attraction, to... Figure 4 The left and right directions, that is, along Figure 4 The axis connecting the first electrode 301 and the second electrode 302 vibrates by repeatedly approaching and separating from each other. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the Si oscillator is, for example, around 1 kHz to several hundred MHz.

[0102] Figure 5The vibrating element 30B shown is a SAW device that utilizes surface waves. SAW (Surface Acoustic Wave) is a type of surface acoustic wave.

[0103] The vibrating element 30B includes a piezoelectric substrate 305, a comb-shaped electrode 306 disposed on the piezoelectric substrate 305, a ground electrode 307, a diffraction grating mounting portion 303, and a diffraction grating 34. When an alternating voltage is applied to the comb-shaped electrode 306, a surface acoustic wave (SAW) is excited through the inverse piezoelectric effect. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the SAW device is, for example, around several hundred MHz to several GHz.

[0104] For devices like the above, optical modulation can also be performed according to the principle described later, in the same way as with AT-cut quartz oscillators, by setting diffraction grating 34.

[0105] On the other hand, when the vibrating element 30 is a quartz oscillator, the extremely high Q value of quartz can be used to generate a high-precision modulation signal. The Q value is an indicator of the sharpness of the resonant peak. In addition, quartz oscillators have the advantage of being less susceptible to disturbances. Therefore, by using the modulation signal modulated by the optical modulator 12 equipped with a quartz oscillator, the sampling signal from the object to be measured 14 can be acquired with high precision.

[0106] 1.1.1.5.4. Optical Modulation Based on Vibrating Elements

[0107] Next, the principle of using the vibrating element 30 to modulate light will be explained.

[0108] Figure 6 This indicates that in the incident light K i A conceptual diagram illustrating the generation of multiple diffracted beams when incident from a direction perpendicular to the surface of the vibrating element 30.

[0109] When the incident light K i When the light is incident on a diffraction grating 34 that undergoes thickness shear vibration along the vibration direction 36, such as Figure 6 As shown, multiple diffracted beams K are generated through the diffraction phenomenon. ns n is the diffracted light K ns The number of times, n = 0, ±1, ±2, ... Furthermore, in Figure 6 In the diffraction grating 34 shown, the one illustrated is not... Figure 3 Instead of showing a blazed diffraction grating, this illustration serves as an example of other diffraction gratings, depicting a diffraction grating formed by repeated concave and convex shapes. Furthermore, in Figure 6 In the text, the diffraction light K is omitted. 0s The illustration.

[0110] exist Figure 6 In the middle, the incident light K iThe light enters from a direction perpendicular to the surface of the vibrating element 30, but this angle of incidence is not particularly limited; the angle of incidence can also be set to be oblique relative to the surface of the vibrating element 30. In the case of oblique incidence, the diffracted light K ns Its direction of travel also changes accordingly.

[0111] Furthermore, depending on the design of the diffraction grating 34, higher-order light with |n|≥2 may not sometimes appear. Therefore, to obtain a stable modulation signal, it is best to set |n|=1. That is, in Figure 2 In the laser interferometer 1, the preferred frequency shifter type optical modulator 12 is configured to use ±1st order diffracted light as reference light L2. This configuration allows for the stabilization of measurements in the laser interferometer 1.

[0112] On the other hand, in the case where higher-order light of |n|≥2 appears from the diffraction grating 34, the optical modulator 12 can be configured to use any diffracted light of ±2nd order or higher as the reference light L2 instead of ±1st order diffracted light. Thus, since higher-order diffracted light can be used, the laser interferometer 1 can be made more frequent and smaller.

[0113] In this embodiment, as an example, the incident light K of the incident light modulator 12 is... i The optical modulator 12 is configured such that the angle between its entry direction and the travel direction of the reference light L2 emitted from the optical modulator 12 is 180°. The following shows... Figures 7 to 9 Three examples will be used to illustrate this.

[0114] Figures 7 to 9 These are descriptions of the composition of incident light K. i A conceptual diagram of an optical modulator 12 whose direction of travel is 180° from the direction of travel of the reference light L2.

[0115] exist Figure 7 In addition to the vibrating element 30, the device also includes a reflector 37. The reflector 37 is configured to reflect the diffracted light K. 1s The light is reflected back to the diffraction grating 34. At this point, the diffracted light K... 1s The angle between the incident angle and the reflection angle in mirror 37 is 180°. As a result, the diffracted light K emitted from mirror 37 and returning to diffraction grating 34... 1s The light is diffracted again at diffraction grating 34, directed toward the incident light K that is incident on the modulator 12. i It travels in the opposite direction to the direction of travel. Therefore, by adding a reflector 37, the aforementioned incident light K can be satisfied. i The condition is that the angle between the direction of entry of the light and the direction of travel of the reference light L2 is 180°.

[0116] Furthermore, by using the reflector 37, the reference light L2 generated by the light modulator 12 becomes light that has undergone two frequency modulations. Therefore, by using the reflector 37, a higher frequency modulation can be achieved compared to using a single vibrating element 30.

[0117] exist Figure 8 In, relative to Figure 6 The configuration causes the vibrating element 30 to tilt. The tilt angle θ at this point... S The incident light K is set to satisfy the aforementioned condition. i The condition is that the angle between the direction of entry of the light and the direction of travel of the reference light L2 is 180°.

[0118] Figure 9 The diffraction grating 34 shown has a blaze angle θ B A blazed diffraction grating. Furthermore, when incident light K travels at an incident angle β relative to the normal N of the surface of the vibrating element 30... i When the light enters the diffraction grating 34, the reference light L2 is relative to the normal N with the blaze angle θ. B The same angle returns. Therefore, by making the incident angle β the same as the blaze angle θ B Equal, which satisfies the aforementioned incident light K i The condition is that the angle between the direction of entry of the light beam and the direction of travel of the reference light L2 is 180°. In this case, since no light is used... Figure 7 The reflector 37 shown is not required. Figure 8 As shown, tilting the vibrating element 30 itself satisfies the aforementioned condition, thus enabling further miniaturization and high-frequency operation of the laser interferometer 1. Especially in the case of a blazed diffraction grating, the configuration that satisfies the aforementioned condition is called the "Litterrow configuration," which also has the advantage of significantly improving the diffraction efficiency of the diffracted light.

[0119] also, Figure 9 The pitch P represents the pitch of the blazed diffraction grating; for 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 adjust the incident light K... i The incident angle β relative to the normal N can also be set to 25°.

[0120] 1.1.1.5.5. Packaging Structure

[0121] Figure 10 This is a cross-sectional view showing an optical modulator 12 with an encapsulation structure.

[0122] Figure 10The optical modulator 12 shown includes a container 70 as a housing, an optical modulation oscillator 120 housed in the container 70, and circuit elements 45 constituting an oscillation circuit 54. Furthermore, the container 70 is hermetically sealed, for example, in a vacuum or other reduced-pressure atmosphere, or in an inert gas atmosphere such as nitrogen or argon.

[0123] 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 terminals and the external terminals.

[0124] Additionally, the opening of the container body 72 is blocked by the cap 74 via a sealing ring (not shown) or a low-melting-point glass or other sealing component. The cap 74 is made of a material that allows laser light to pass through, such as glass.

[0125] 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 bonding wire, a bonding metal, or other conductive material (not shown).

[0126] 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. In addition, circuitry other than the oscillation circuit 54 described later may be disposed on the circuit element 45.

[0127] 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. This suppresses external noise from entering the drive signal Sd, or conversely, prevents 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 external environmental influences. Therefore, miniaturization of the sensor head 51 is achieved, and the reliability of the laser interferometer 1 is improved.

[0128] Furthermore, 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 independent packaging structures. Additionally, although not shown, other circuit elements constituting the oscillation circuit 54 can also be housed in container 70. Moreover, container 70 can be provided as needed and may be omitted.

[0129] 1.1.2. Current-to-voltage converter

[0130] The current-to-voltage converter 531, also known as a transimpedance amplifier (TIA), converts the photocurrent (photodetector signal) output from the photodetector 10 into a voltage signal and outputs it as a photodetector signal.

[0131] A current-to-voltage converter 531 and a demodulation circuit 52 are configured between them. Figure 1 The ADC532 is shown. The ADC532 is an analog-to-digital converter that converts analog signals into digital signals at a specified number of sampling bits. The ADC532 is located on the sensor head 51.

[0132] The optical system 50 may also include multiple light-receiving elements 10. In this case, by providing a differential amplifier circuit between the multiple light-receiving elements 10 and the current-to-voltage converter 531, differential amplification processing can be performed on the photocurrent, thereby improving the signal-to-noise ratio (S / N ratio) of the photodetector signal. Furthermore, differential amplification processing can also be performed on voltage signals.

[0133] 1.1.3. Oscillator Circuit

[0134] like Figure 1 As shown, the oscillation circuit 54 outputs a drive signal Sd, which is input to the optical modulator 12 of the optical system 50. Additionally, the oscillation circuit 54 outputs a reference signal Ss, which is input to the demodulation circuit 52.

[0135] The oscillation circuit 54 is any circuit capable of causing the oscillating element 30 to oscillate; there are no particular limitations, and various circuit configurations can be used. As an example of circuit configuration, Figure 11 The diagram below illustrates the configuration of a single-stage inverter oscillator circuit.

[0136] 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.

[0137] Circuit element 45 is an inverter IC. Terminals X1 and X2 of circuit element 45 are connected to the internal inverter of circuit element 45, respectively. Terminal GND is connected to ground potential, and terminal Vcc is connected to power supply potential. Terminal Y is used for oscillation output.

[0138] A first capacitor Cg is connected between terminal X1 and the ground potential. Additionally, a limiting resistor Rd and a second capacitor Cd are connected in series between terminal X2 and the ground potential, starting from terminal X2. Furthermore, one end of the 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.

[0139] 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.

[0140] Figure 12 This is an example of a circuit diagram representing the LCR equivalent circuit of the vibrating element 30.

[0141] 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.

[0142] exist Figure 11 In the oscillation circuit 54 shown, 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 equation (a).

[0143]

[0144] Therefore, the oscillation frequency f output from terminal Y of the oscillation circuit 54 osc It is given by the following equation (b).

[0145]

[0146] f Q It is the natural frequency of the vibrating element 30.

[0147] According to equation (b) above, by appropriately changing the load capacitance C L It can control the oscillation frequency f of the signal output from terminal Y. osc Make minor adjustments.

[0148] 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).

[0149]

[0150] Here, since C1 << C0 and C1 << C L Therefore, Δf is approximately given by the following equation (d).

[0151]

[0152] 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.

[0153] Here, when the vibrating element 30 is fixed in the container 70, for example, if it is subjected to expansion stress caused by temperature through the fixing part, the natural frequency f Q The change occurs. Furthermore, if the vibrating element 30 is tilted, the natural frequency f... Q It changes due to the influence of gravity and other factors caused by its own weight.

[0154] In the oscillator circuit 54, even if the inherent frequency f is reduced for such reasons... Q The change has occurred; based on the above equation (d), the oscillation frequency f osc It also changes in a manner linked to this change. That is, 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. By stabilizing the displacement amplitude, the modulation characteristics of the optical modulator 12 are stabilized, thus improving the demodulation accuracy of the sampled signal in the demodulation circuit 52.

[0155] As an example, the preferred value is Δf = |f osc -f Q |≤3000[Hz], more preferably Δf≤600[Hz].

[0156] In addition, the laser interferometer 1 includes a demodulation circuit 52 and an oscillation circuit 54. The demodulation circuit 52 demodulates the sampled signal from the object to be measured 14 from the photodetector signal based on photocurrent (received signal) according to the reference signal Ss. The oscillation circuit 54 operates by using the vibration element 30 as a signal source, and... Figure 1 The demodulation circuit 52 outputs a reference signal Ss, as shown.

[0157] Based on this configuration, even the natural frequency f of the vibrating element 30 Q Changes can also alter the oscillation frequency f of the oscillation circuit 54. osc The change is related to the natural frequency f of the vibrating element 30. QThe 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, thereby stabilizing the modulation characteristics of the optical modulator 12. Consequently, the demodulation accuracy of the sampled signal in the demodulation circuit 52 can be improved.

[0158] 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. Therefore, since 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, the changes in the modulation signal with 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 from the measurement object 14 can be improved.

[0159] Furthermore, since the oscillation circuit 54 has low power consumption, the power saving of the laser interferometer 1 can be easily achieved.

[0160] Furthermore, as described above, the vibrating element 30 is preferably a quartz oscillator. This allows for the generation of a high-precision modulation signal using the extremely high Q value of quartz. Consequently, the sampling signal from the object being measured 14 can be acquired with high precision.

[0161] Alternatively, a signal generator, such as a function generator or a signal generator, can be used instead of the oscillation circuit 54.

[0162] 1.2. Main Body

[0163] Figure 1 and Figure 2 The main body 59 shown has a demodulation circuit 52.

[0164] The demodulation circuit 52 performs demodulation processing as follows: it demodulates the sampled signal from the object to be measured 14 based on the optical detection signal output from the current-to-voltage converter 531. 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. Since different physical quantities can be obtained in this way, it can function as a displacement meter or a velocity meter, thus enabling high functionality of the laser interferometer 1.

[0165] The circuit configuration of the demodulation circuit 52 is set according to the modulation processing method. In the laser interferometer 1 according to this embodiment, an optical modulator 12 equipped with a vibrating element 30 is used. The vibrating element 30 is a simple harmonic oscillation element, and therefore its vibration speed changes constantly within the period. Therefore, the modulation frequency also changes with time, and existing demodulation circuits cannot be used directly.

[0166] Existing demodulation circuits refer to circuits that demodulate a sampled signal from a light detection signal containing a modulated signal modulated using an acousto-optic modulator (AOM). In an acousto-optic modulator, the modulation frequency does not change. Therefore, existing demodulation circuits can demodulate a sampled signal from a light detection signal containing a modulated signal with a fixed modulation frequency, but they cannot directly demodulate a modulated signal containing a modulated signal modulated by a light modulator 12 with a varying modulation frequency.

[0167] therefore, Figure 1 The demodulation circuit 52 shown includes a preprocessing unit 53 and a demodulation processing unit 55. The light detection signal output from the current-to-voltage converter 531 first passes through the preprocessing unit 53 and is then guided to the demodulation processing unit 55. The preprocessing unit 53 performs preprocessing on the light detection signal. Through this preprocessing, a signal that can be demodulated using a conventional demodulation circuit is obtained. Therefore, in the demodulation processing unit 55, the sampling signal from the object to be measured 14 is demodulated using a known demodulation method.

[0168] The aforementioned functions of the demodulation circuit 52 are implemented, for example, by hardware including a processor, memory, external interface, input unit, and display unit. Specifically, this is achieved by the processor reading and executing a program stored in the memory. Furthermore, these components can communicate with each other via an internal bus.

[0169] Examples of processors include CPUs (Central Processing Units) and DSPs (Digital Signal Processors). Alternatively, software can be executed using FPGAs (Field-Programmable Gate Arrays) or ASICs (Application Specific Integrated Circuits).

[0170] Examples of storage devices include HDD (Hard Disk Drive), SSD (Solid State Drive), EEPROM (Electrically Erasable Programmable Read-Only Memory), ROM (Read-Only Memory), and RAM (Random Access Memory).

[0171] External interfaces include, for example, digital input / output ports such as USB (Universal Serial Bus) and Ethernet (registered trademark) ports.

[0172] As an input unit, examples include various input devices such as keyboards, mice, touch panels, and touchpads. As a display unit, examples include liquid crystal display panels and organic EL (Electroluminescence) display panels.

[0173] 1.2.1. Composition of the pretreatment unit

[0174] 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. Furthermore, AGC stands for Automatic Gain Control.

[0175] The optical detection signal output from the current-to-voltage converter 531 is split into two signals, a first signal S1 and a second signal S2, at the bifurcation point 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.

[0176] An ADC 533 is connected between the oscillation circuit 54 and the second delay adjuster 537. The ADC 533 is an analog-to-digital converter that converts analog signals into digital signals at a specified number of sampling bits. The ADC 533 is located on the sensor head 51.

[0177] 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.

[0178] 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.

[0179] 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.

[0180] 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 caused by the second bandpass filter 535 (described later). Through this delay adjustment, the delay time generated by the filter circuits passing through the first bandpass filter 534 through which the first signal S1 passes is made consistent between the second bandpass filter 535 and the third bandpass filter 539 through which the second signal S2 passes. After passing through the first delay adjuster 536, the first signal S1 is input to the adder 542 via the first AGC 540.

[0181] The second signal S2 is input to the multiplier 538 after passing through the second bandpass filter 535 configured on the second signal path ps2. In the multiplier 538, the second signal S2 is multiplied by the reference signal Ss output from the second delay adjuster 537. Specifically, the reference signal Ss output from the oscillator circuit 54 is multiplied by cos(ω... m The reference signal Ss, represented by t), is digitally converted in the ADC533, its phase is adjusted in the second delay adjuster 537, and then input to the multiplier 538. ω m t is the angular frequency of the modulation signal of the optical modulator 12, and t is time. Then, after passing through the third bandpass filter 539, the second signal S2 is input to the adder 542 via the second AGC 541.

[0182] Adder 542 outputs an output signal that is proportional to the sum of the first signal S1 and the second signal S2. Furthermore, the circuit configuration of the preprocessing unit 53 described above is an example and is not limited to this.

[0183] 1.2.2. Basic Principles of Preprocessing

[0184] Next, the basic principle of preprocessing in preprocessing unit 53 will be explained. 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 being measured 14 also varies in simple harmonic motion along the optical axis will be considered. Here, E... m E d , Set as

[0185] E m =a m {cos(ω0t+B sinω m t+φ m )+i sin(ω0t+B sinω m t+φ m )} (1)

[0186] E d =ad {cos(ω0t+A sinω d t+φ d )+i sin(ω0t+A sinω d t+φ d (2)

[0187] φ=φ m -φ d (3)

[0188] At that time, the light detection signal I output from the current-to-voltage converter 531 PD Theoretically, it can be expressed by the following formula.

[0189] I PD =<|E m +E d | 2 >

[0190] =<|E m 2 +E d 2 +2E m E d |>

[0191] =a m 2 +a d 2 +2a m a d cos(B sinω m tA sinω d t+φ) (4)

[0192] In addition, E m E d , ω m ω d , ω0, a m a d As shown below.

[0193] E m Electric field component of the modulation signal from the optical modulator

[0194] E d Electric field component from the sampling signal of the object being measured.

[0195] φ m The initial phase of the modulation signal from the optical modulator

[0196] φ d The initial phase of the sampling signal from the object being measured.

[0197] φ: Optical path phase difference of the laser interferometer

[0198] ω m Angular frequency of the modulation signal from the optical modulator

[0199] ω d Angular frequency of the sampled signal from the object being measured.

[0200] ω0: Angular frequency of the emitted light from the light source

[0201] a m :coefficient

[0202] a d :coefficient

[0203] In addition, in equation (4), <> represents time average.

[0204] The first and second terms of equation (4) above represent the DC component, and the third term represents the AC component. If this AC component is set as I... PD·AC , then I PD·AC As shown in the following formula.

[0205] I PD·AC =2a m a d cos(B sinω m tA sinω d t+φ)

[0206] =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)

[0207]

[0208]

[0209] A: Phase shift of the sampled signal

[0210] f dmax Doppler frequency shift of the sampled signal

[0211] f d Frequency of the sampled signal

[0212] B: Phase shift of the modulated signal

[0213] f mmaxDoppler frequency shift of the modulated signal

[0214] f m Frequency of the modulating signal

[0215] Here, we know of v-th degree Bessel functions as shown in equations (8) and (9).

[0216] cos{ζsin(2πf v t)}=J0(ζ)+2J2(ζ)cos(2·2πf v t)+2J4(ζ)cos(4·2πf v t)+… (8)

[0217] sin{ζsin(2πf v t)}=2J1(ζ)sin(1·2πf v t)+2J3(ζ)sin(3·2πf v t)+… (9)

[0218] If we use the Bessel functions of equations (8) and (9) above to perform a series expansion of equation (5), it can be transformed as shown in equation (10) below.

[0219] 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)

[0220] Where J0(B), J1(B), J2(B), ... are Bessel coefficients.

[0221] If the frequency band is modified as described above, then theoretically it can be said that a bandpass filter can be used to extract the frequency band corresponding to a specific number of frequencies.

[0222] Therefore, in the aforementioned preprocessing unit 53, the light detection signal is preprocessed according to the following process based on this theory.

[0223] First, the photodetector signal output from the current-to-voltage converter 531 is split into two signals, a first signal S1 and a second signal S2, at the bifurcation point jp1. The first signal S1 passes through a first bandpass filter 534. The center angular frequency of the first bandpass filter 534 is set to ω. m Therefore, the first signal S1 after passing through the first bandpass filter 534 is represented by the following formula.

[0224] I pass1 =J1(B){-cos(ω m t+A sinω d t-φ)+cos(ω m tA sinω d t+φ)}

[0225] =-2J1(B)sin(ω) m t)sin(A sinω d t-φ) (11)

[0226] 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.

[0227]

[0228] The second signal S2, after passing through the second bandpass filter 535, is multiplied by the reference signal Ss by the multiplier 538. The second signal S2 after passing through the multiplier 538 is represented by the following formula.

[0229]

[0230] 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.

[0231]

[0232] Then, the phase of the first signal S1 represented by the above formula (11) is adjusted by the first delay adjuster 536, and the amplitude is adjusted by the first AGC 540.

[0233] 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.

[0234] Furthermore, the first signal S1 and the second signal S2 are added together by adder 542. The result of the addition is represented by the following equation (15).

[0235] I 53 =cos(ω m t+A sinω d t-φ) (15)

[0236] As shown in equation (15) above, the result of the addition is that unnecessary terms disappear, and necessary terms can be extracted. In other words, the addition result I expressed by equation (15) is... 53 It is a signal obtained by extracting the frequency modulation component. The result of this addition is I. 53 The signal is input to the demodulation processing unit 55.

[0237] 1.2.3. Composition of the demodulation processing unit

[0238] The demodulation processing unit 55 performs demodulation processing as follows: it demodulates the sampled signal from the object to be measured 14 based on the signal output from the preprocessing unit 53. There are no particular limitations on the demodulation processing method; a well-known method of quadrature detection can be cited. Quadrature detection is a method of demodulation processing that involves externally mixing mutually orthogonal signals from the input signal.

[0239] 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 operator 558, and an output circuit 559.

[0240] Multipliers 551 and 552 are circuits that generate an output signal proportional to the product of the two input signals. Phase shifter 553 is a circuit that generates an output signal with its amplitude unchanged but its phase reversed. The first low-pass filter 555 and the second low-pass filter 556 are filters that cut off signals in the high-frequency band.

[0241] Divider 557 is a circuit that generates an output signal proportional to the quotient of the two input signals. Arctangent calculus 558 is a circuit that outputs the arctangent of the input signals. Output circuit 559 calculates the phase value obtained by arctangent calculus 558. Calculate the phase This information comes from the object being measured, 14. Furthermore, in the output circuit 559, phase connection is performed when there is a 2π phase jump between adjacent points through phase expansion processing. Moreover, the displacement of the object being measured, 14, is calculated based on the obtained phase information. Thus, a displacement meter is implemented. Additionally, the velocity of the object being measured, 14, can be determined from the displacement. Thus, a speed meter is implemented.

[0242] Furthermore, the circuit configuration of the demodulation processing unit 55 described above is an example and is not limited thereto. For example, the demodulation processing unit 55 is not limited to a digital circuit, but can also be an analog circuit. The analog circuit may also include an F / V converter circuit or a ΔΣ counter circuit.

[0243] 1.2.4. Demodulation processing in the demodulation processing unit

[0244] In the demodulation process, firstly, the signal output from the preprocessing unit 53 is split into two parts using the bifurcation section jp2. In the multiplier 551, one of the split signals is multiplied by the coefficient of performance (cos(ω)) output from the oscillation circuit 54. m The reference signal Ss is represented by t). In multiplier 552, the split signal is multiplied by -sin(ωt), which shifts the phase of the reference signal Ss output from oscillation circuit 54 by -90° through phase shifter 553. 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 shifted by 90° from each other.

[0245] The signal after passing through multiplier 551 passes through first low-pass filter 555, and then is input as signal x to divider 557. The signal after passing through multiplier 552 passes through second low-pass filter 556, and then is input as signal y to divider 557. In divider 557, the signal y is divided by the signal x, and the output y / x is passed through arctangent operator 558 to obtain the output atan(y / x).

[0246] Then, by passing the output atan(y / x) through the output circuit 559, the phase is determined. As information from the object being measured 14, the output circuit 559 performs phase unrolling processing to connect the phases when there is a 2π phase jump between adjacent points. Furthermore, the displacement of the object being measured 14 can be calculated from the phase information. Thus, a displacement meter is implemented. Additionally, the velocity can be derived from the displacement. Thus, a speed meter is implemented.

[0247] On the other hand, frequency information can also be obtained in the output circuit 559. The speed of the object 14 to be measured can be calculated based on the frequency information.

[0248] 1.3. Effects of the First Implementation Method

[0249] As described above, the laser interferometer 1 according to the first embodiment includes a laser source 2, an optical modulator 12, a light receiving element 10, an optical coupler 4, a collimator 21 (first collimator), a collimator 22 (second collimator), an optical fiber 61 (first optical wiring), an optical fiber 62 (second optical wiring), an optical fiber 63 (third optical wiring), and an optical fiber 64 (fourth optical wiring).

[0250] Laser source 2 emits outgoing light L1 (first laser). Optical modulator 12 includes a vibrating element 30, which modulates the outgoing light L1 to generate a reference light L2 (second laser) containing a modulation signal. Light receiving element 10 receives the reference light L2 and object light L3 (third laser) and outputs a received signal, wherein the object light L3 contains a sampling signal generated by the reflection of the outgoing light L1 by the object to be measured 14. Outgoing light L1, reference light L2, and object light L3 are incident on optical coupler 4, which has the function of splitting outgoing light L1 and splitting the combined light L4 of reference light L2 and object light L3. Collimator 21 (first collimator) parallelizes the outgoing light L1 split by optical coupler 4 and emits it toward optical modulator 12. Collimator 22 (second collimator) parallelizes the outgoing light L1 split by optical coupler 4 and emits it toward object to be measured 14.

[0251] Optical fiber 61 optically connects the laser source 2 to the optical coupler 4, allowing the outgoing light L1 emitted from the laser source 2 to enter the optical coupler 4. Optical fiber 62 optically connects the light-receiving element 10 to the optical coupler 4, allowing the combined light L4, split by the optical coupler 4, to enter the light-receiving element 10. Optical fiber 63 optically connects the collimator 21 to the optical coupler 4. Optical fiber 64 optically connects the collimator 22 to the optical coupler 4.

[0252] With this configuration, since optical fibers 61-64 are used as optical cabling when connecting optical elements such as the laser source 2, optical coupler 4, light receiving element 10, collimator 21, optical modulator 12, and collimator 22, the number of connection points that allow light to propagate in free space can be reduced. Therefore, alignment of the optical system 50 can be easily performed, and the need for re-alignment is reduced. Furthermore, while there are limits to the miniaturization of optical elements at connection points requiring alignment, such limitations are not present in the optical system 50, and position adjustment devices required for alignment are not needed. Therefore, miniaturization and weight reduction of the optical system 50 can be easily achieved. Moreover, the optical fibers 61-64 are flexible, allowing light to propagate even when bent. Therefore, the arrangement of optical elements can be optimized, and space-saving features of the optical system 50 can be easily achieved.

[0253] Furthermore, in this embodiment, the optical coupler 4 is a fiber optic coupler. Moreover, as described above, the first optical cabling, the second optical cabling, the third optical cabling, and the fourth optical cabling are optical fibers 61 to 64.

[0254] With this configuration, since the fiber optic coupler is formed by fusion splicing optical fibers, an integrated structure is achieved, integrating the optical coupler 4 with optical fibers 61-64. This enables the realization of an optical system 50 with minimal optical loss.

[0255] Furthermore, the laser interferometer 1 according to this embodiment has a movable sensor head 51 and a main body 59. A laser light source 2, an optical modulator 12, a light-receiving element 10, an optical coupler 4, a collimator 21 (first collimator), and a collimator 22 (second collimator) are disposed on the sensor head 51. "Disposed on the sensor head 51" means that these optical elements are housed within a housing (not shown) of the sensor head 51 or mounted outside the housing.

[0256] With this configuration, only the electrical wiring (not shown) connecting the sensor head 51 and the main body 59 is exposed to the external space, while all optical fibers 61 to 64 are located in the sensor head 51. Therefore, the exposure of optical fibers 61 to 64 to the external space can be prevented, thereby suppressing the influence of disturbances on the optical signals propagating in the optical fibers 61 to 64. The influence of disturbances can be exemplified by unexpected changes in the optical signal caused by vibration or expansion / contraction of the optical fibers 61 to 64, temperature changes, etc. By suppressing such disturbances, the signal-to-noise ratio (S / N ratio) of the received signal output from the light-receiving element 10 can be improved. As a result, the accuracy of measuring the displacement or velocity of the object 14, which can be measured using the laser interferometer 1, can be improved.

[0257] Furthermore, the laser interferometer 1 according to this embodiment includes a demodulation circuit 52 and an oscillation circuit 54. The oscillation circuit 54 operates by using the vibration element 30 as a signal source, and as follows... Figure 1 The demodulation circuit 52 outputs a reference signal Ss. Based on the reference signal Ss, the demodulation circuit 52 demodulates the sampled signal from the object being measured 14 from the received light signal.

[0258] Based on this configuration, even the natural frequency f of the vibrating element 30 Q Changes can also alter 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, thereby stabilizing the modulation characteristics of the optical modulator 12. Consequently, the demodulation accuracy of the sampled signal in the demodulation circuit 52 can be improved.

[0259] 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. Therefore, since 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, the changes in the modulation signal with 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 from the measurement object 14 can be improved.

[0260] In addition, the oscillation circuit 54 consumes less power than function generators or signal generators, thus making it easy to reduce the power consumption of the laser interferometer 1.

[0261] 1.4. First variation of the first embodiment

[0262] Next, a first variation of the first embodiment will be described.

[0263] Figure 13 This is a perspective view of the sensor head 51 of the laser interferometer 1A according to the first modification of the first embodiment.

[0264] The first modified example will be described below, but the description will focus on the differences from the first embodiment, omitting descriptions of identical items. Furthermore, in Figure 13 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0265] The laser interferometer 1A in the first modified example also includes a mounting substrate 9 disposed on the sensor head 51. Furthermore, as... Figure 13 As shown, the laser source 2, the optical modulator 12, the light receiving element 10, the optical coupler 4, the collimator 21 (first collimator) and the collimator 22 (second collimator) are mounted on the mounting substrate 9.

[0266] With this configuration, the aforementioned optical elements can be fixed to the mounting substrate 9, thus enabling further miniaturization of the sensor head 51 and improved operability. Furthermore, this configuration also helps improve durability against disturbances such as vibration, shock, and temperature changes.

[0267] Examples of substrates 9 for mounting the sensor head include resin substrates, ceramic substrates, and metal substrates. Alternatively, the substrate 9 can also be a circuit board. A circuit board is a substrate containing built-in electrical wiring. Therefore, a portion of the electrical wiring responsible for the electrical connection between the laser light source 2, the light-receiving element 10, and the light modulator 12 and the main body 59 can be incorporated into the circuit board. This allows for further miniaturization and ease of manufacturing of the sensor head 51.

[0268] Furthermore, similar to the first embodiment described above, in this first modification, the arrangement of the laser light source 2, the light receiving element 10, and the optical modulator 12 also has a high degree of freedom. Therefore, the arrangement can be optimized by taking into account the mutual influence of electromagnetic noise generated from these components.

[0269] Furthermore, the optocoupler 4 is preferably fixed to the mounting substrate 9 at two or more locations. As a result, even if vibration or impact is applied to the sensor head 51, its influence can be suppressed from affecting the optocoupler 4.

[0270] In addition, collimators 21 and 22 can be fixed to the surface of the mounting substrate 9, or they can be embedded in the recesses or through holes provided on the mounting substrate 9.

[0271] In this first variation, the same effect as the first embodiment can be obtained.

[0272] 1.5. Second variation of the first embodiment

[0273] Next, a second variation of the first embodiment will be described.

[0274] Figure 14 This is a schematic configuration diagram of the sensor head 51 of the laser interferometer 1B according to the second variation of the first embodiment.

[0275] The second variation will be described below, but the description will focus on the differences from the first embodiment, omitting descriptions of identical items. Furthermore, in... Figure 14 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0276] like Figure 14 As shown, the laser interferometer 1B in the second modification is the same as the laser interferometer 1 in the first embodiment, except that it has a collimator 23 (third collimator).

[0277] Figure 14The collimator 23 (third collimator) shown is positioned between the laser source 2 and the optical coupler 4 to parallelize the emitted light L1 (first laser). The collimator 23 is an optical element (optical component) disposed between the laser source 2 and the optical coupler 4; for example, an aspherical lens can be used. The emitted light L1 from the laser source 2 passes through the collimator 23 and enters the optical fiber 61.

[0278] By setting up such a collimator 23, the incident efficiency of the emitted light L1 relative to the optical fiber 61 can be improved. That is, the coupling loss between the laser source 2 and the optical fiber 61 can be suppressed.

[0279] In addition, the collimator 23 may also include optical elements other than aspherical lenses.

[0280] In this second variation, the same effect as the first embodiment can be obtained.

[0281] 2. Second Implementation Method

[0282] Next, the laser interferometer according to the second embodiment will be described.

[0283] Figure 15 This is a schematic diagram showing the sensor head 51 of the laser interferometer 1C according to the second embodiment.

[0284] The second embodiment will be described below, but the description will focus on the differences from the embodiment described above, omitting descriptions of identical items. Furthermore, in Figure 15 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0285] In the first embodiment described above, the laser light source 2, the optical modulator 12, the light receiving element 10, the optical coupler 4, the collimator 21 (first collimator), and the collimator 22 (second collimator) are all disposed on the sensor head 51.

[0286] In contrast, such as Figure 15 As shown, the laser interferometer 1C according to this embodiment has a movable sensor head 51 and a main body 59, with a collimator 22 (second collimator) disposed on the sensor head 51. On the other hand, the laser light source 2, the light modulator 12, the light receiving element 10, the optical coupler 4, and the collimator 21 (first collimator) are disposed on the main body 59. "Disposed on the main body 59" means that these optical elements are housed within a housing (not shown) of the main body 59 or mounted outside the housing.

[0287] With this configuration, the number of optical elements provided on the sensor head 51 can be reduced compared to the first embodiment. As a result, the sensor head 51 can be miniaturized.

[0288] In this second embodiment, the same effect as in the first embodiment can be obtained.

[0289] 3. Third Implementation Method

[0290] Next, the laser interferometer according to the third embodiment will be described.

[0291] Figure 16 This is a schematic diagram showing the sensor head 51 of the laser interferometer 1D according to the third embodiment.

[0292] The third embodiment will be described below, but the description will focus on the differences from the first embodiment, omitting descriptions of identical items. Furthermore, in... Figure 16 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0293] like Figure 16 As shown, the laser interferometer 1D according to this embodiment has a movable sensor head 51 and a main body 59. An optical modulator 12, a collimator 21 (first collimator), and a collimator 22 (second collimator) are provided on the sensor head 51. On the other hand, a laser source 2, a light receiving element 10, and an optical coupler 4 are provided on the main body 59.

[0294] With this configuration, since collimators 21 and 22 are located in the sensor head 51 and optical coupler 4 is located in the main body 59, optical fibers 63 and 64 are wound between the sensor head 51 and the main body 59. Optical fiber 63 serves as the medium for optically connecting collimator 21 and optical coupler 4 and propagating reference light L2. Optical fiber 64 serves as the medium for optically connecting collimator 22 and optical coupler 4 and propagating object light L3. Because both optical fibers 63 and 64 are wound to the outside, both reference light L2 and object light L3 are affected by disturbances. Therefore, the effects of disturbances in reference light L2 and object light L3 are canceled out or mutually suppressed. As a result, the signal-to-noise ratio (S / N ratio) of the received signal can be improved, or the S / N ratio can be stabilized.

[0295] Furthermore, in this embodiment, the number of optical elements disposed on the sensor head 51 can be reduced compared to the first embodiment. As a result, the sensor head 51 can be miniaturized.

[0296] In this third embodiment, the same effect as in the first embodiment can be obtained.

[0297] 4. Fourth Implementation Method

[0298] Next, the laser interferometer according to the fourth embodiment will be described.

[0299] Figure 17 This is a schematic diagram showing the sensor head 51 of the laser interferometer 1E according to the fourth embodiment.

[0300] The fourth embodiment will be described below, but the description will focus on the differences from the first embodiment, omitting descriptions of identical items. Furthermore, in... Figure 17 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0301] The laser interferometer 1E involved in this embodiment has the same configuration as the laser interferometer 1 involved in the first embodiment, except that... Figure 17 The device also includes an optical isolator 5 disposed between the laser source 2 and the optical coupler 4, otherwise it is the same as the laser interferometer 1 according to the first embodiment. The optical isolator 5 has the function of reducing the return light L5 from the optical coupler 4 toward the laser source 2.

[0302] Here, the optical coupler 4 is a 2×2 type coupler. Therefore, the combined light L4 from one of the branches enters the light-receiving element 10, and the combined light L4 from the other branch is directed towards the laser source 2. The light returning from the optical coupler 4 to the laser source 2 is called the "return light L5". If the return light L5 enters the laser source 2, the laser oscillation in the laser source 2 becomes unstable. This instability in the laser oscillation causes a decrease in the signal-to-noise ratio (S / N) of the received light signal.

[0303] Therefore, as described above, the laser interferometer 1E according to this embodiment includes an optical isolator 5. The optical isolator 5 is disposed between the laser source 2 and the optical coupler 4 to reduce the return light L5 from the optical coupler 4 toward the laser source 2.

[0304] With this configuration, the intensity of the returned light L5 incident on the laser source 2 can be reduced. This allows for the stabilization of laser oscillations within the laser source 2. Consequently, the phase of the emitted light L1 is also stabilized, thus improving the signal-to-noise ratio (S / N) of the received signal.

[0305] The principles underlying the optical isolator 5 can be polarization-dependent or polarization-independent, for example. Furthermore, the forms of the optical isolator 5 can be free-space or fiber-coupled, for example.

[0306] Furthermore, the required performance of the optical isolator 5 can be expressed, for example, by optical density (OD value), in its ability to block the return light L5. Preferably, the ability of the optical isolator 5 to block the return light L5 satisfies OD ≥ 4. This allows for sufficient stabilization of laser oscillation.

[0307] In this fourth embodiment, the same effect as in the first embodiment can also be obtained.

[0308] 5. Fifth Implementation Method

[0309] Next, the laser interferometer according to the fifth embodiment will be described.

[0310] Figure 18 This is a schematic diagram showing the sensor head 51 of the laser interferometer 1F according to the fifth embodiment.

[0311] The fifth embodiment will be described below, but the description will focus on the differences from the first embodiment, omitting descriptions of identical items. Furthermore, in... Figure 18 In this document, the same reference numerals are given to configurations that are the same as those in the first embodiment.

[0312] The laser interferometer 1F involved in this embodiment has the same configuration as the laser interferometer 1 involved in the first embodiment, except that... Figure 18 The instrument also includes an optical path length changing unit 15, which is otherwise the same as the laser interferometer 1 according to the first embodiment. The optical path length changing unit 15 has the function of changing the optical path length of the optical path through which the emitted light L1 emitted from the collimator 21 propagates.

[0313] Here, in order to improve the signal-to-noise ratio (S / N) of the received light signal, it is necessary to suppress the frequency fluctuations, i.e., the phase fluctuations, of the emitted light L1 emitted from the laser source 2. However, the frequency fluctuations of the emitted light L1 depend on the type of laser source 2 and are therefore difficult to suppress easily. Therefore, in this embodiment, by providing the optical path length changing unit 15, the decrease in the S / N ratio of the received light signal due to the frequency fluctuations of the emitted light L1 can be suppressed, and even the measurement accuracy of the displacement of the object 14 can be improved. The operation of such an optical path length changing unit 15 will be explained below.

[0314] In demodulation circuit 52, the sampled signal from the object to be measured 14 is demodulated based on the received light signal. Furthermore, the displacement of the object to be measured 14 can be determined based on the sampled signal. When the measurement accuracy of this displacement is set to Δd, the measurement accuracy Δd is expressed by the following formula (I).

[0315]

[0316] λ: Wavelength of the emitted light L1

[0317] Δφ: Phase of the sampled signal

[0318] n: Refractive index of the atmosphere

[0319] d: Figure 18 The difference between the optical path length from point A to point B2 and the optical path length from point A to point C2 (optical path difference)

[0320] Δf: Frequency fluctuation (phase fluctuation) of the emitted light L1

[0321] f: Frequency of emitted light L1

[0322] Δn: Fluctuation in the refractive index of the atmosphere

[0323] The measurement accuracy Δd is represented by the above equation (I), which includes a first term containing the wavelength λ, a second term containing the optical path difference d and the frequency fluctuation Δf (phase fluctuation) of the emitted light L1, and a third term containing the optical path difference d and the fluctuation Δn of the refractive index of the atmosphere. In the above equation (I), when the optical path difference d is 0, the second and third terms on the right side are also 0. In this case, the displacement measurement accuracy Δd is theoretically unaffected by the frequency fluctuation Δf (phase fluctuation) of the emitted light L1 or the fluctuation Δn of the refractive index of the atmosphere. On the other hand, when the optical path difference d is not 0, the frequency fluctuation Δf or the fluctuation Δn of the refractive index of the atmosphere affects the displacement measurement accuracy Δd. In particular, the frequency fluctuation Δf of the emitted light L1 is sometimes a large value depending on the type of laser source 2. Therefore, depending on the type of laser source 2, the measurement accuracy Δd of the displacement of the object 14 may deteriorate.

[0324] Therefore, in this embodiment, the optical path length changing unit 15 is activated to make the optical path difference d close to 0, that is, to make... Figure 18 The optical path length from point A to point B2 is close to that from point A to point C2. The optical path length changing unit 15 has the function of changing the optical path length from point A to point B2. By making the optical path difference d close to 0, the displacement measurement accuracy Δd is less affected by the frequency fluctuation Δf [Hz] of the emitted light L1. As a result, the displacement of the object to be measured 14 can be measured with high accuracy regardless of the type of laser source 2. In addition, the velocity of the object to be measured 14 can also be calculated from the displacement. Furthermore, the optical path length refers to the optical distance. Figure 18 Point A is the center of optical coupler 4, point B1 is the connection point between optical fiber 63 and collimator 21, point B2 is the light reflection point of optical modulator 12, point C1 is the connection point between optical fiber 64 and collimator 22, and point C2 is the light reflection point of the object to be measured 14.

[0325] Figure 18 The optical path length changing unit 15 shown includes a first reflective element 151 and a second reflective element 152, and a driving unit 153 that drives the first reflective element 151. The first reflective element 151 and the second reflective element 152 are optical elements that switch the optical path 20 of the emitted light L1. The driving unit 153 changes the physical distance between the first reflective element 151 and the second reflective element 152 by moving the first reflective element 151. As a result, the optical path length between point A and point B2 is changed.

[0326] The drive unit 153 generates a driving force, causing the first reflective element 151 to move in the direction connecting the first reflective element 151 and the second reflective element 152. Additionally, the drive unit 153 holds the first reflective element 151 at the target position. Furthermore, the drive unit 153 can be configured to move the second reflective element 152 without moving the first reflective element 151, or it can be configured to move both the first reflective element 151 and the second reflective element 152. Moreover, the direction of movement is not limited as long as the optical path length of the optical path 20 can be changed.

[0327] As the drive unit 153, a device that moves the first reflective element 151 in a straight line is used, such as a linear platform, an electric actuator, a piezoelectric actuator, etc.

[0328] Figure 18 The first reflecting element 151 shown includes right-angle prism reflectors 154a and 154b and a substrate 156 supporting the right-angle prism reflectors 154a and 154b. The right-angle prism reflectors 154a and 154b are optical elements having light-reflecting surfaces 150 that intersect the light path 20 at a 45° angle. Furthermore, the right-angle prism reflectors 154a and 154b are arranged such that the angle between their light-reflecting surfaces 150 and each other is 90°. Thus, the light path 20 folds back the right-angle prism reflectors 154a and 154b as a pair and faces the second reflecting element 152. The substrate 156 supports multiple pairs of right-angle prism reflectors 154a and 154b together.

[0329] Figure 18 The second reflective element 152 shown includes right-angle prism reflectors 155a and 155b and a substrate 157 supporting the right-angle prism reflectors 155a and 155b. The right-angle prism reflectors 155a and 155b are optical elements each having a light-reflecting surface 150 that intersects the light path 20 at a 45° angle. Furthermore, the right-angle prism reflectors 155a and 155b are arranged such that the angle between their light-reflecting surfaces 150 and each other is 90°. Thus, the light path 20 extending from the first reflective element 151 folds back towards the first reflective element 151 after the right-angle prism reflectors 155a and 155b are folded back as a pair. The substrate 157 supports multiple pairs of right-angle prism reflectors 155a and 155b together.

[0330] The right-angle prism reflectors 154a, 154b, 155a, and 155b are highly accurate and readily available. Therefore, the optical elements used as the first reflecting element 151 and the second reflecting element 152 are useful.

[0331] Furthermore, the configuration of the optical path length changing unit 15 is not limited to the above configuration as long as it can change the optical path length of the optical path 20. For example, the number of units, the structure of the right-angle prism reflector, and the path of the optical path 20 can also be different from those described above. Alternatively, a roof-type prism reflector or an integrated prism reflector can be used instead of the above-described units.

[0332] As described above, the laser interferometer 1F according to this embodiment also includes an optical path length changing unit 15. The optical path length changing unit 15 is disposed between the collimator 21 (first collimator) and the optical modulator 12, and changes the optical path length of the optical path 20 in which the emitted light L1 (first laser) emitted from the collimator 21 propagates.

[0333] With this configuration, since the optical path length of the optical path 20 can be freely changed, the optical path difference d in the above equation (I) can be made close to 0, and preferably d can be made to be 0. Therefore, the displacement measurement accuracy Δd is less affected by the frequency fluctuation Δf of the emitted light L1. As a result, regardless of the type of laser source 2, the displacement of the object 14 can be measured with high precision.

[0334] Furthermore, although the VCSEL (Vertical-Cavity Surface-Emitting Laser) and FP-LD (Fabry-Perot Laser Diode) in the aforementioned laser source 2 have a large frequency fluctuation Δf in the emitted light L1, they are inexpensive. Therefore, by using them as laser source 2, the cost of the laser interferometer 1F can be reduced.

[0335] in addition, Figure 18 The optical path length of the optical path 20 shown is adjusted according to the physical distance between optical elements or the refractive index of the atmosphere. That is, in this embodiment, when the optical path difference d is 0, the following equation (II) holds.

[0336] n f L fq +n0L q =n f L fs +n0L s …(II)

[0337] n f The refractive index of the fiber core

[0338] n0: Refractive index of the atmosphere

[0339] L fq : Figure 18 Propagation distance in optical fiber 63

[0340] L fs : Figure 18 Propagation distance in optical fiber 64

[0341] L q : Figure 18 The physical distance between point B1 and point B2

[0342] L s : Figure 18 The physical distance between point C1 and point C2

[0343] The optical path length of the optical path 20 is adjusted using a standard sample whose displacement or velocity of vibration is known. Specifically, the drive unit 153 is operated by measuring the displacement or velocity against the standard sample in a manner that makes the measured value close to the known value. Furthermore, when the measured value is obtained that is closest to the known value, the drive unit 153 is stopped, and the object to be measured 14 is measured in this state.

[0344] As mentioned above, Figure 18 The optical path length changing unit 15 shown has a first reflective element 151 and a driving unit 153 as movable optical elements. The first reflective element 151 has the function of changing the optical path length of the optical path 20 by moving it, that is, the optical path length of the optical path 20 through which the emitted light L1 (first laser) emitted from the collimator 21 (first collimator) propagates.

[0345] With this optical path length changing unit 15, the moving distance of the first reflective element 151 based on the drive unit 153 can be easily matched with the change in the optical path length of the optical path 20. Therefore, the optical path length changing unit 15, which allows for easy adjustment of the optical path length, can be realized. Furthermore, the actuator used as the drive unit 153 is readily available, and the adjustment of the moving distance is highly accurate. Therefore, with this configuration of the optical path length changing unit 15, the optical path length can be adjusted with high precision.

[0346] In this fifth embodiment, the same effect as in the first embodiment can be obtained.

[0347] 6. Sixth Implementation Method

[0348] Next, the laser interferometer according to the sixth embodiment will be described.

[0349] Figure 19 This is a schematic diagram showing the sensor head 51 of the laser interferometer 1G according to the sixth embodiment.

[0350] The sixth embodiment will be described below, but the description will focus on the differences from the fifth embodiment, omitting descriptions of identical items. Furthermore, in... Figure 19 In this document, the same reference numerals are given to configurations that are the same as those in the fifth embodiment.

[0351] like Figure 19As shown, the laser interferometer 1G according to this embodiment is the same as the laser interferometer 1F according to the fifth embodiment, except for the different configuration of the optical path length changing unit 15G. The optical path length changing unit 15G has the function of changing the optical path length of the optical path through which the emitted light L1 emitted from the collimator 21 propagates.

[0352] In the laser interferometer 1F according to the fifth embodiment described above, the optical path length changing unit 15 has a first reflecting element 151 and a second reflecting element 152. In contrast, in the laser interferometer 1G according to the sixth embodiment, as... Figure 19 As shown, the optical path length changing unit 15G includes a refractive index variable medium 171 and an input unit 172. The refractive index variable medium 171 is a medium disposed in the optical path 20 in which the emitted light L1 travels, and its refractive index changes according to the input control signal. The input unit 172 inputs a control signal to the refractive index variable medium 171.

[0353] In this optical path length changing section 15G, the optical path 20 passes through the refractive index variable 171. Moreover, by changing the refractive index of the refractive index variable 171, the optical path length of the optical path 20 can be changed.

[0354] The refractive index variable 171 is a transparent medium disposed on the optical path 20. For example, it is a medium whose refractive index can be changed by using electric field, magnetic field, heat, light, etc., as control parameters and inputting them as control signals. Among these, a polymer-dispersed liquid crystal is known as a medium for using an electric field as a control parameter. The refractive index of a polymer-dispersed liquid crystal varies depending on the magnitude of the applied electric field. By using a polymer-dispersed liquid crystal as the refractive index variable 171, the refractive index can be changed by using an easily controllable electric field as a control parameter. Therefore, the configuration of the optical path length changing unit 15G can be further simplified.

[0355] Furthermore, as an example of a refractive index variable 171 other than a polymer-dispersed liquid crystal, a medium having a temperature-dependent refractive index can be cited. Examples of such media include inorganic materials such as quartz glass and organic materials such as acrylic resin. In this case, the input unit 172 is a temperature adjustment unit that inputs heat as a control parameter; for example, a heat exchange element such as a Peltier element can be cited.

[0356] As described above, in the laser interferometer 1G involved in this embodiment, Figure 19 The optical path length changing unit 15G shown has a refractive index variable 171 and an input unit 172. The refractive index of the refractive index variable 171 changes according to the input of a control signal. The input unit 172 inputs a control signal to the refractive index variable 171.

[0357] The optical path length changing section 15G has no movable parts, thus exhibiting high durability. Therefore, the reliability of the laser interferometer 1G can be improved.

[0358] also, Figure 19 The optical path length of the optical path 20 shown is adjusted according to the physical distance between optical elements or the refractive index of the atmosphere. That is, in this embodiment, when the optical path difference d is 0, the following equation (III) holds. Furthermore, Figure 19 Point B3 is the end of the refractive index variable 171 on the side of point B1, and point B4 is the end of the refractive index variable 171 on the side of point B2.

[0359] n f L fq +n0(L q1 +L q3 )+n r L q2 =n f L fs +n0L s …(III)

[0360] n f The refractive index of the fiber core

[0361] n0: Refractive index of the atmosphere

[0362] nr: Refractive index of refractive index variant 171

[0363] L fq : Figure 19 Propagation distance in optical fiber 63

[0364] L fs : Figure 19 Propagation distance in optical fiber 64

[0365] L q1 : Figure 19 The physical distance between point B1 and point B3

[0366] L q2 The physical length of the refractive index variable 171 ( Figure 19 (physical length from point B3 to point B4)

[0367] L q3 : Figure 19 The physical distance between point B4 and point B2

[0368] The optical path length of optical path 20 is adjusted using a standard sample whose displacement or velocity of vibration is known. Specifically, the input unit 172 is operated by measuring the displacement or velocity against the standard sample and making the measured value close to the known value. Furthermore, when the measured value is obtained that is closest to the known value, the input unit 172 is stopped, and the object to be measured 14 is measured in this state.

[0369] In this sixth embodiment, the same effect as in the first embodiment can also be obtained.

[0370] The laser interferometer of the present invention has been described above with reference to the illustrated embodiments. However, the laser interferometer of the present invention is not limited to the described embodiments, and the configuration of each part can be replaced with any configuration having the same function. In addition, other arbitrary configurations may be added to the laser interferometer involved in the described embodiments.

[0371] Furthermore, the laser interferometer of the present invention may also include any two or more of the described embodiments and their variations. For example, it may be a combination of the fourth embodiment with an optical isolator and the fifth embodiment with a movable optical element (a first composite embodiment), or it may be a combination of the fourth embodiment and the sixth embodiment with a variable refractive index body (a second composite embodiment). Additionally, the first composite embodiment is based on the first embodiment, but may also be based on the second or third embodiment. Similarly, the second composite embodiment is also based on the first embodiment, but may also be based on the second or third embodiment.

[0372] In addition to the aforementioned displacement gauges and velocities, the laser interferometer of the present invention can also be applied to vibratory meters, inclinometers, rangefinders (length measuring devices), etc. Furthermore, as applications of the laser interferometer of the present invention, examples include optical comb interferometry technology capable of measuring distance, 3D imaging, and beam splitting, as well as fiber optic gyroscopes such as angular velocity sensors, accelerometers, and angular acceleration sensors.

[0373] Furthermore, while the various embodiments and modifications described herein have a so-called Michelson-type interferometric optical system, the laser interferometer of the present invention can also be applied to laser interferometers having other types of interferometric optical systems, such as Mach-Zehnder-type interferometric optical systems.

Claims

1. A laser interferometer, characterized in that, have: The laser source emits the first laser beam. An optical modulator, comprising a vibrating element, uses the vibrating element to modulate the first laser to generate a second laser containing a modulated signal; A light-receiving element receives the second laser and the third laser, and outputs a light-receiving signal, wherein the third laser includes a sampling signal generated by the reflection of the first laser by the object being measured; An optical coupler is provided, wherein the first laser, the second laser, and the third laser are incident on the optical coupler, and the optical coupler has the function of splitting the first laser and splitting the combined beam of the second laser and the third laser; A first collimator parallelizes the first laser beam that has been bisected by the optical coupler and directs it toward the optical modulator. The second collimator parallelizes the first laser beam that has been split off by the optical coupler and directs it toward the object being measured. The first optical fiber connects the laser source to the optical coupler, so that the first laser emitted from the laser source enters the optical coupler. The second optical fiber connects the light-receiving element to the optical coupler, so that the combined light split by the optical coupler enters the light-receiving element. The third optical fiber connects the first collimator to the optical coupler. The fourth optical fiber connects the second collimator to the optical coupler. An optical path length changing unit is disposed between the first collimator and the optical modulator to change the optical path length of the optical path propagated by the first laser emitted from the first collimator; The demodulation circuit demodulates the sampled signal from the received light signal based on the reference signal; as well as An oscillation circuit uses the vibrating element as a signal source to operate and outputs a reference signal corresponding to the natural frequency of the vibrating element.

2. The laser interferometer according to claim 1, characterized in that, The optical coupler is a fiber optic coupler. The first optical cable, the second optical cable, the third optical cable, and the fourth optical cable are optical fibers.

3. The laser interferometer according to claim 1 or 2, characterized in that, The laser interferometer has the following features: A movable sensor head; and Main body, The laser source, the optical modulator, the light-receiving element, the optical coupler, the first collimator, and the second collimator are disposed on the sensor head.

4. The laser interferometer according to claim 3, characterized in that, The laser interferometer includes a mounting substrate disposed on the sensor head. The laser source, the optical modulator, the light-receiving element, the optical coupler, the first collimator, and the second collimator are mounted on the mounting substrate.

5. The laser interferometer according to claim 1 or 2, characterized in that, The laser interferometer has the following features: A movable sensor head; and Main body, The second collimator is disposed on the sensor head. The laser source, the optical modulator, the light-receiving element, the optical coupler, and the first collimator are disposed on the main body.

6. The laser interferometer according to claim 1 or 2, characterized in that, The laser interferometer has the following features: A movable sensor head; and Main body, The optical modulator, the first collimator, and the second collimator are disposed on the sensor head. The laser source, the light-receiving element, and the optical coupler are disposed on the main body.

7. The laser interferometer according to claim 1, characterized in that, The laser interferometer includes an optical isolator, which is disposed between the laser source and the optical coupler to reduce the return light from the optical coupler toward the laser source.

8. The laser interferometer according to claim 1, characterized in that, The laser interferometer includes a third collimator, which is disposed between the laser source and the optical coupler to parallelize the first laser.

9. The laser interferometer according to claim 1, characterized in that, The optical path length changing unit has: Movable optical elements, whose movement changes the length of the optical path; and The drive unit drives the movable optical element.

10. The laser interferometer according to claim 1, characterized in that, The optical path length changing unit has: The refractive index is variable, changing according to the input of a control signal; and The input unit inputs the control signal to the refractive index variable.

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