Laser interferometer

Abstract

To provide a laser interferometer capable of miniaturizing an optical system and facilitating alignment work.SOLUTION: A laser light source that emits a first laser light, an optical modulator that includes a vibration element and modulates the first laser light using the vibration element to generate a second laser light including a modulated signal, and a third laser light including a sample signal generated by reflecting the second laser light and the first laser light on a measurement target; A laser interferometer comprising a light receiving element configured to output a light receiving signal, an optical coupler having a function of branching a first laser light and a function of branching a merged light of a second laser light and a third laser light, a first collimator configured to collimate the first laser light branched by the optical coupler, a second collimator configured to collimate 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.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a laser vibrometer as a device for measuring the vibration velocity of an object. This laser vibrometer irradiates a laser beam onto the object to be measured and measures the vibration velocity based on the scattered laser beam that has undergone a Doppler shift.

[0003] The laser vibrometer described in Patent Document 1 specifically includes a vibration element such as a piezoelectric element. The vibration element shifts the frequency of the laser light based on the vibration frequency. The object being measured also shifts the frequency of the laser light according to its vibration state. The light that has been frequency-shifted by the vibration element and the object being measured returns to the half mirror as return light. The half mirror reflects the return light to a photodetector, reflects a portion of the laser light, reflects it off a reflecting mirror, transmits it again, and then transmits it to the photodetector as reference light. The return light and the reference light are then photomixed by the photodetector, and the beat frequency is electrically extracted. The vibration of the object being measured is then detected as a frequency displacement and quantified using a frequency-modulated wave demodulator and a signal processing device.

[0004] The laser vibrometer described in Patent Document 1 includes optical elements such as a semiconductor laser that emits laser light, a half mirror, a polarizing beam splitter, a λ / 4 plate, a reflecting mirror, a vibration element, and a photodetector. Among these, the polarizing beam splitter transmits the light emitted from the laser, causes it to enter the vibration element, reflects it, causes it to enter the object to be measured, and then reflects it again and causes it to enter the vibration element. Furthermore, as mentioned above, the half mirror reflects the returning light and transmits the reference light, causing them to enter the photodetectors. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-285898 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in the laser vibrometer described in Patent Document 1, various optical elements are optically connected to one another. This requires securing space to accommodate each optical element, making it difficult to miniaturize the optical system. Furthermore, to extract a highly accurate beat frequency, high precision is required for the alignment of the optical elements. This makes alignment time-consuming. Furthermore, an adjustment mechanism is required to perform the alignment, which also makes it difficult to miniaturize the optical system.

[0007] For the above reasons, it is necessary to reduce the size of the optical system and to simplify the alignment process. [Means for solving the problem]

[0008] A laser interferometer according to an application example of the present invention includes: a laser light source that emits a first laser beam; an optical modulator including a vibration element, the optical modulator modulating the first laser light using the vibration element to generate a second laser light including a modulation signal; a light-receiving element that receives the second laser light and a third laser light including a sample signal generated when the first laser light is reflected by a measurement object, and outputs a light-receiving signal; an optical coupler into which the first laser light, the second laser light, and the third laser light are incident, the optical coupler having a function of splitting the first laser light and a function of splitting a combined light of the second laser light and the third laser light; a first collimator that collimates one of the first laser beams branched by the optical coupler and outputs the collimated first laser beam toward the optical modulator; a second collimator that collimates the other of the first laser beams branched by the optical coupler and emits the collimated laser beam toward the object to be measured; a first optical wiring that optically connects the laser light source and the optical coupler and causes the first laser light emitted from the laser light source to be incident on the optical coupler; a second optical wiring that optically connects the light receiving element and the optical coupler and causes the combined light branched by the optical coupler to be incident on the light receiving element; a third optical wiring that optically connects the first collimator and the optical coupler; a fourth optical wiring that optically connects the second collimator and the optical coupler; The present invention is characterized by comprising: [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a functional block diagram showing a laser interferometer according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the configuration of the sensor head unit shown in FIG. [Figure 3] FIG. 3 is a perspective view showing a first configuration example of the optical modulator shown in FIG. [Figure 4] FIG. 10 is a plan view showing a part of a second configuration example of the optical modulator. [Figure 5] FIG. 10 is a plan view showing a third configuration example of the optical modulator. [Figure 6] 1 is a conceptual diagram illustrating the generation of multiple diffracted beams when incident light Ki is incident on the surface of a vibration element in a direction perpendicular to the surface. [Figure 7] FIG. 10 is a conceptual diagram illustrating an optical modulator configured so that the angle formed between the traveling direction of incident light Ki and the traveling direction of reference light L2 is 180°. [Figure 8] FIG. 10 is a conceptual diagram illustrating an optical modulator configured so that the angle formed between the traveling direction of incident light Ki and the traveling direction of reference light L2 is 180°. [Figure 9] FIG. 10 is a conceptual diagram illustrating an optical modulator configured so that the angle formed between the traveling direction of incident light Ki and the traveling direction of reference light L2 is 180°. [Figure 10] FIG. 1 is a cross-sectional view showing an optical modulator having a package structure. [Figure 11] FIG. 1 is a circuit diagram showing the configuration of a single-stage inverter oscillator circuit. [Figure 12] 1 is an example of a circuit diagram showing an LCR equivalent circuit of a vibration element. [Figure 13] FIG. 10 is a perspective view showing a sensor head portion of a laser interferometer according to a first modified example of the first embodiment. [Figure 14] FIG. 10 is a schematic configuration diagram showing a sensor head portion of a laser interferometer according to a second modified example of the first embodiment. [Figure 15] FIG. 10 is a schematic configuration diagram showing a sensor head unit of a laser interferometer according to a second embodiment. [Figure 16] FIG. 10 is a schematic configuration diagram showing a sensor head unit of a laser interferometer according to a third embodiment. [Figure 17] FIG. 10 is a schematic configuration diagram showing a sensor head unit of a laser interferometer according to a fourth embodiment. [Figure 18] FIG. 10 is a schematic configuration diagram showing a sensor head unit of a laser interferometer according to a fifth embodiment. [Figure 19] FIG. 10 is a schematic configuration diagram showing a sensor head unit of a laser interferometer according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0011] FIG. 1 is a functional block diagram showing a laser interferometer 1 according to the first embodiment. The laser interferometer 1 shown in Figure 1 has a sensor head unit 51 equipped with an optical system 50, a current-voltage converter 531, and an oscillator circuit 54, and a main body unit 59 equipped with a demodulation circuit 52 to which a received light signal from the optical system 50 is input.

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

[0013] 1.1.1.Optical system As shown in FIG. 2, the optical system 50 includes a laser light 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.

[0014] An optical fiber 61 (first optical wiring) is provided between the laser light source 2 and the optical coupler 4. The optical fiber 61 optically connects the laser light source 2 and the optical coupler 4 together.

[0015] An optical fiber 62 (second optical wiring) 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.

[0016] An optical fiber 63 (third optical wiring) 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 together.

[0017] An optical fiber 64 (fourth optical wiring) 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 together.

[0018] As described above, in the optical system 50, optical elements such as the laser light source 2, optical coupler 4, light-receiving element 10, collimator 21, optical modulator 12, and collimator 22 are optically connected to one another via optical fibers 61-64. In such an optical system 50, fewer connection points through which light propagates in free space are required when connecting optical elements. This facilitates alignment and reduces the need for realignment. Furthermore, while there are limitations to miniaturizing optical elements at connection points that require alignment, given the adjustment range, the optical system 50 obviates such limitations and eliminates the need for position adjustment devices and the like required for alignment. Furthermore, the optical fibers 61-64 are flexible, allowing light to propagate even when bent.

[0019] The laser light source 2 emits output light L1 (laser light). The optical coupler 4 splits the output light L1 into two. One of the output light L1 split by the optical coupler 4 is irradiated onto an optical modulator 12 equipped with a vibration element 30 and reflected as reference light L2 containing a modulated signal, which is a Doppler signal derived from the vibration element 30. The other output light L1 split by the optical coupler 4 is irradiated onto a measurement object 14 and reflected as object light L3 containing a sample signal, which is a Doppler signal derived from the measurement object 14. The reference light L2 and object light L3 are combined by the optical coupler 4 to become combined light L4, which is then split into two. The light-receiving element 10 receives one of the combined light L4 split by the optical coupler 4 and converts it into an electrical signal.

[0020] The sensor head unit 51 is movable. "Movable" means that it is portable and has a size that allows for high installation flexibility. The position and posture of the movable sensor head unit 51 can be adjusted so that the emitted light L1 is irradiated onto the measurement object 14. Therefore, the sensor head unit 51 may be mounted on a position adjustment device such as a goniostage, if necessary.

[0021] On the other hand, the main body 59 does not need to be movable, and therefore can be installed on a storage rack, a table, or the like.

[0022] Each part of the optical system 50 will be further described below. Laser light source The laser light source 2 is a laser light source that emits coherent output light L1. A light source with a linewidth in the MHz range or less is preferably used as the laser light source 2. Specific examples include gas lasers such as He-Ne lasers, and semiconductor laser elements such as DFB-LDs (Distributed Feedback Laser Diodes), FBG-LDs (Fiber Bragg Grating Laser Diodes), VCSELs (Vertical Cavity Surface Emitting Lasers), and FP-LDs (Fabry-Perot Laser Diodes).

[0023] It is particularly preferable that the laser light source 2 is a semiconductor laser element. This allows the laser light source 2 to be particularly small and lightweight. This allows the laser interferometer 1 to be made smaller. In particular, the sensor head 51 of the laser interferometer 1, which houses the optical system 50, can be made smaller and lighter, which improves the operability of the laser interferometer 1, such as the degree of freedom in installing the sensor head 51.

[0024] Optical Coupler The optical coupler 4 is a 2x2 type coupler with four optical input / output terminals. This optical coupler 4 has the functions of splitting the incident output light L1, joining the incident reference light L2 and object light L3 to obtain joined light L4, and splitting the joined light L4.

[0025] Examples of the optical coupler 4 include an optical fiber type coupler and an optical waveguide type coupler.

[0026] Of these, an optical fiber coupler is preferably used for the optical coupler 4. The optical fiber coupler is formed, for example, by fusing optical fibers together. Therefore, the optical fiber coupler is a structure in which the optical coupler 4, which is the fused portion of the optical fibers, and the optical fibers 61 to 64 (first optical wiring to fourth optical wiring) extending from the fused portion are integrated. Therefore, by using an optical fiber coupler, it is possible to realize an optical system 50 with low optical loss. Another advantage is that the optical system 50 can be easily assembled, since the connection and alignment work between the optical coupler 4 and the optical fibers 61 to 64 is not required. Note that the optical coupler 4 and the optical fibers 61 to 64 may be separate structures.

[0027] Furthermore, the optical fibers 61 to 64 may each be a glass optical fiber or a plastic optical fiber.

[0028] On the other hand, an optical waveguide coupler is composed of, for example, an optical waveguide having a branch core portion. Furthermore, an optical waveguide coupler can be easily integrated with an optical waveguide wiring extending from the branch core portion. Therefore, the optical waveguide coupler may also be a structure in which the optical coupler 4, which is the branch core portion, and the optical waveguide wirings, which are the first to fourth optical wirings, are integrated. The optical waveguide wirings can be easily formed along any path in a sheet-like member. Therefore, even when an optical waveguide coupler including an optical waveguide wiring is used, it is possible to easily achieve miniaturization, weight reduction, space saving, etc. of the optical system 50.

[0029] Examples of materials constituting the optical waveguide coupler include ferroelectrics, compound semiconductors, glass, and plastics.

[0030] The branching ratio of the optical coupler 4 is not particularly limited, but is preferably 20:80 or more and 80:20 or less, and more preferably 40:60 or more and 60:40 or less. This prevents the light intensity after branching from becoming extremely biased, making it possible to prevent a decrease in the S / N ratio (signal-to-noise ratio) of the received light signal.

[0031] Furthermore, the laser light source 2 and the optical fiber 61, the light receiving element 10 and the optical fiber 62, the collimator 21 and the optical fiber 63, and the collimator 22 and the optical fiber 64 may be physically and optically connected using an intermediary such as an optical adhesive, or may be optically connected via a small free space. In particular, with the former connection method, once the alignment work of the connection points is completed during the manufacturing stage of the optical system 50, no further alignment work is required unless the optical elements are repaired or replaced. This improves the maintainability of the optical system 50. Furthermore, the former connection method is highly resistant to disturbances such as vibration, impact, and temperature changes.

[0032] 1.1.1.3.Photodetector One of the combined light beams L4 branched by the optical coupler 4 is incident on the light receiving element 10. The light receiving element 10 receives this combined light beam L4 and outputs a light receiving signal. By demodulating this light receiving signal into a sample signal using a method described below, it is possible to ultimately determine the movement of the measurement object 14, i.e., the vibration velocity and displacement. The light receiving element 10 may be, for example, a photodiode.

[0033] Collimator The collimator 21 is an optical element (optical component) disposed between the optical fiber 63 and the optical modulator 12, and an example thereof is an aspherical lens. The collimator 21 collimates the output light L1 that has been branched by the optical coupler 4 and propagated through the optical fiber 63, and emits the collimated output light L1 toward the optical modulator 12. The emitted output light L1 propagates through free space and enters the optical modulator 12. The reference light L2 generated by the optical modulator 12 propagates through free space and enters the optical fiber 63 via the collimator 21. Note that in this specification, "collimation" does not only refer to converting divergent light into perfectly parallel light, but also refers to correcting the beam divergence angle of the divergent light in a direction that reduces it. Therefore, for example, the output light L1 and the reference light L2 that have passed through the collimator 21 do not necessarily need to be perfectly parallel light.

[0034] Alignment work is required to optically connect the collimator 21 and the optical modulator 12. This alignment work includes the work of adjusting the position of the collimator 21 to collimate the emitted light L1, the work of making the emitted light L1 incident on the optical modulator 12, the work of adjusting the installation angle of the optical modulator 12 to couple the reference light L2 to the collimator 21, etc.

[0035] The collimator 22 is an optical element (optical component) disposed between the optical fiber 64 and the measurement object 14, and an example thereof is an aspherical lens. The collimator 22 collimates the output light L1 that has been branched by the optical coupler 4 and propagated through the optical fiber 64, and emits the collimated light toward the measurement object 14. The emitted output light L1 propagates through free space and is incident on the measurement object 14. In addition, the object light L3 generated by the measurement object 14 propagates through free space and is incident on the optical fiber 64 via the collimator 22.

[0036] Alignment work is required to optically connect the collimator 22 and the measurement object 14. This alignment work includes adjusting the position of the collimator 22 to collimate the emitted light L1, making the emitted light L1 incident on the measurement object 14, adjusting the installation angle of the sensor head unit 51 to couple the object light L3 to the collimator 22, and the like.

[0037] Each of the collimators 21 and 22 may include an optical element other than an aspherical lens.

[0038] Optical Modulator FIG. 3 is a perspective view showing a first configuration example of the optical modulator 12 shown in FIG.

[0039] 1.1.1.5.1. Overview of the first example of optical modulator configuration The frequency shifter type optical modulator 12 has an optical modulation oscillator 120. The optical modulation oscillator 120 shown in FIG.

[0040] The vibration element 30 is made of a material that, when a voltage is applied, repeats a vibration mode in which the vibration is distorted in a direction along the surface. In this configuration example, the vibration element 30 is a quartz crystal AT resonator that vibrates in a thickness-shear mode along a vibration direction 36 in a high frequency region in the MHz band. A diffraction grating 34 is formed on the surface of the vibration element 30. The diffraction grating 34 has grooves 32 that have components that intersect with the vibration direction 36, i.e., a plurality of linear grooves 32 that extend in a direction that intersects with the vibration direction 36.

[0041] The substrate 31 has a front surface 311 and a back surface 312 which are opposite surfaces. The vibration elements 30 are arranged on the front surface 311. The front surface 311 is also provided with pads 33 for applying a voltage to the vibration elements 30. Meanwhile, the back surface 312 is also provided with pads 35 for applying a voltage to the vibration elements 30.

[0042] The size of the substrate 31 is, for example, about 0.5 mm to 10.0 mm in length. The thickness of the substrate 31 is, for example, about 0.10 mm to 2.0 mm. As an example, the shape of the substrate 31 is a square with each side measuring 1.6 mm, and the thickness is 0.35 mm.

[0043] The size of the vibration element 30 is, for example, about 0.2 mm or more and 3.0 mm or less in terms of the long side, and the thickness of the vibration element 30 is, for example, about 0.003 mm or more and 0.5 mm or less.

[0044] As an example, the shape of the vibrating element 30 is a square with sides of 1.0 mm and a thickness of 0.07 mm. In this case, the vibrating element 30 oscillates at a fundamental oscillation frequency of 24 MHz. Note that by changing the thickness of the vibrating element 30 and taking into account overtones, the oscillation frequency can be adjusted within a range from 1 MHz to 1 GHz.

[0045] In FIG. 3, the diffraction grating 34 is formed on the entire surface of the vibration element 30, but it may be formed on only a part of the surface.

[0046] The magnitude of the optical modulation by the optical modulator 12 is given by the dot product of the differential wave vector between the wave vector of the output light L1 entering the optical modulator 12 and the wave vector of the reference light L2 exiting from the optical modulator 12, and the vector in the vibration direction 36 of the vibration element 30. In this configuration example, the vibration element 30 vibrates in a thickness-shear manner, but because this vibration is an in-plane vibration, optical modulation cannot be achieved even if light is incident perpendicularly to the surface of the vibration element 30 alone. Therefore, in this configuration example, a diffraction grating 34 is provided in the vibration element 30, making optical modulation possible based on a principle described below.

[0047] The diffraction grating 34 shown in Fig. 3 is a blazed diffraction grating. A blazed diffraction grating is a diffraction grating whose cross section has a stepped shape. The linear grooves 32 of the diffraction grating 34 are arranged so that their extension direction is perpendicular to the vibration direction 36.

[0048] 1 and 2 to the vibration element 30 shown in Fig. 3, the vibration element 30 oscillates. The electric power (driving power) required for oscillation of the vibration element 30 is not particularly limited, but is small, about 0.1 μW to 100 mW. Therefore, the drive signal Sd output from the oscillation circuit 54 can be used to oscillate the vibration element 30 without amplifying it.

[0049] Furthermore, conventional optical modulators sometimes require a structure to maintain the temperature of the optical modulator, making it difficult to reduce their volume. Furthermore, conventional optical modulators have a problem in that they consume a lot of power, making it difficult to reduce the size and power consumption of the laser interferometer. In contrast, in this configuration example, the volume of the vibration element 30 is very small and the power required for oscillation is also small, making it easy to reduce the size and power consumption of the laser interferometer 1.

[0050] 1.1.1.5.2.Method of forming a diffraction grating The method for forming the diffraction grating 34 is not particularly limited, but one example is to create a mold using a mechanical ruling engine, and then form the grooves 32 on an electrode formed on the surface of the vibration element 30 using a nanoimprinting method. The reason for forming the grooves on the electrode is that, in principle, a quartz AT resonator can generate high-quality thickness-shear vibration on the electrode. The grooves 32 do not necessarily have to be formed on the electrode, but may also be formed on the surface of a material in the non-electrode portion. Instead of nanoimprinting, other processing methods such as exposure and etching, electron beam lithography, and focused ion beam (FIB) processing may also be used.

[0051] Alternatively, a diffraction grating may be formed on the chip of a quartz crystal AT resonator using a resist material, and a metal film or a dielectric multilayer mirror film may be provided on top of the grating. By providing a metal film or a mirror film, the reflectance of the diffraction grating 34 can be increased.

[0052] Furthermore, a resist film may be formed on a chip or wafer of a quartz crystal AT resonator, processed by etching, and then removed. A metal film or mirror film may then be formed on the processed surface. In this case, the resist material is removed, eliminating the effects of moisture absorption by the resist material and improving the chemical stability of the diffraction grating 34. Furthermore, by providing a highly conductive metal film such as Au or Al, it can also be used as an electrode for driving the resonator element 30.

[0053] The diffraction grating 34 may be formed using techniques such as anodic alumina (porous alumina).

[0054] 1.1.1.5.3.Other Configuration Examples of Optical Modulators The vibrating element 30 is not limited to a quartz vibrator, but may be, for example, a Si vibrator, a surface acoustic wave (SAW) device, a ceramic vibrator, or the like.

[0055] Fig. 4 is a plan view showing a part of a second configuration example of the optical modulator 12. Fig. 5 is a plan view showing a third configuration example of the optical modulator 12.

[0056] 4 is a Si vibrator manufactured from a Si substrate using MEMS technology. MEMS (Micro Electro Mechanical Systems) stands for micro-electromechanical systems.

[0057] The vibration element 30A includes a first electrode 301 and a second electrode 302 adjacent to each other on the same plane with a gap therebetween, a diffraction grating mounting portion 303 provided on the first electrode 301, and a diffraction grating 34 provided on the diffraction grating mounting portion 303. The first electrode 301 and the second electrode 302 vibrate, for example, by electrostatic attraction as a driving force, in the left-right direction in FIG. 4, i.e., along an axis connecting the first electrode 301 and the second electrode 302 shown in FIG. 4, so as to repeatedly approach and move away from each other. This allows in-plane vibration to be imparted to the diffraction grating 34. The oscillation frequency of the Si vibrator is, for example, from about 1 kHz to several hundred MHz.

[0058] The vibrating element 30B shown in Fig. 5 is a SAW device that uses surface waves. SAW (Surface Acoustic Wave) stands for surface acoustic wave.

[0059] The vibration element 30B includes a piezoelectric substrate 305, a comb-shaped electrode 306 provided on the piezoelectric substrate 305, a ground electrode 307, a diffraction grating mounting portion 303, and a diffraction grating 34. When an AC voltage is applied to the comb-shaped electrode 306, a surface acoustic wave is excited due to the inverse piezoelectric effect. This allows in-plane vibration to be applied to the diffraction grating 34. The oscillation frequency of the SAW device is, for example, from several hundred MHz to several GHz.

[0060] In the above-described device, by providing a diffraction grating 34, optical modulation becomes possible according to the principle described below, as in the case of a quartz crystal AT oscillator.

[0061] On the other hand, if the vibration element 30 is a quartz crystal oscillator, a highly accurate modulation signal can be generated by utilizing the extremely high Q value of the quartz crystal. The Q value is an index that indicates the sharpness of the resonance peak. Furthermore, a quartz crystal oscillator has the advantage of being less susceptible to external disturbances. Therefore, by using a modulation signal modulated by the optical modulator 12 equipped with a quartz crystal oscillator, a sample signal derived from the measurement object 14 can be acquired with high accuracy.

[0062] 1.1.1.5.4.Light modulation by vibration elements Next, the principle of modulating light using the vibration element 30 will be described.

[0063] FIG. 6 shows the incident light K i 1 is a conceptual diagram illustrating the generation of multiple diffracted beams when incident light.

[0064] Light K is incident on a diffraction grating 34 that is vibrating in thickness shear along a vibration direction 36. i When the incident light is incident on the surface, the diffraction phenomenon causes multiple diffracted light beams K nsoccurs. n is the diffracted light K ns The order of the diffraction grating 3 shown in FIG. 4 shows a diffraction grating made of repeated concaves and convexes as an example of a different diffraction grating from the blazed diffraction grating shown in FIG. 3. Also, in FIG. 6, diffracted light K 0s The illustration of do.

[0065] In Figure 6, the incident light K i is incident on the surface of the vibration element 30 from a direction perpendicular to the surface of the vibration element 30, but this incident angle is not particularly limited, and the incident angle may be set so that the light is incident obliquely on the surface of the vibration element 30. When the light is incident obliquely, the diffracted light K ns The direction of travel is also It changes accordingly.

[0066] Depending on the design of the diffraction grating 34, higher-order light of |n| ≥ 2 may not appear. Therefore, to obtain a stable modulated signal, it is desirable to set |n| = 1. That is, in the laser interferometer 1 of FIG. 2, the frequency shifter-type optical modulator 12 is preferably arranged so that the ±1st-order diffracted light is used as the reference light L2. This arrangement enables stable measurement by the laser interferometer 1.

[0067] On the other hand, when high-order light of |n|≧2 emerges from the diffraction grating 34, the optical modulator 12 may be arranged so that any of the ±2nd-order or higher-order diffracted light is used as the reference light L2, rather than the ±1st-order diffracted light. This allows the use of high-order diffracted light, thereby achieving higher frequency and miniaturization of the laser interferometer 1.

[0068] In this embodiment, as an example, incident light K i The optical modulator 12 is configured so that the angle formed between the direction of incidence of the reference beam L2 and the direction of travel of the reference beam L2 emitted from the optical modulator 12 is 180°. Three examples will be described below with reference to Figs. 7 to 9.

[0069] 7 to 9 show the incident light K i 1 is a conceptual diagram illustrating an optical modulator 12 configured so that the angle formed between the traveling direction of the reference light L1 and the traveling direction of the reference light L2 is 180°.

[0070] In FIG. 7, a mirror 37 is provided in addition to the vibration element 30. The mirror 37 reflects the diffracted light K 1s The mirror 37 is arranged to reflect the light back to the diffraction grating 34. Diffracted light K 1s The angle between the incident angle of the light and the reflection angle of the mirror 37 is 180°. As a result, the diffracted light K emitted from the mirror 37 and returned to the diffraction grating 34 1s is a diffraction grating The incident light K is diffracted again at 34 and enters the optical modulator 12. i Therefore, by adding the mirror 37, the incident light K i This satisfies the condition that the angle formed between the incident direction of the reference beam L1 and the traveling direction of the reference beam L2 is 180°.

[0071] Furthermore, by passing the reference light L2 through the mirror 37 in this way, the reference light L2 generated by the optical modulator 12 is subjected to frequency modulation twice. Therefore, by using the mirror 37 in combination, it is possible to perform frequency modulation at a higher frequency than when the vibration element 30 is used alone.

[0072] In Fig. 8, the vibration element 30 is tilted relative to the arrangement in Fig. 6. The tilt angle θ S is the incident light K i The angle formed by the incident direction of the reference light L1 and the traveling direction of the reference light L2 is set to 180°.

[0073] The diffraction grating 34 shown in FIG. B The blazed diffraction grating has the following structure: incident light K propagating at an incident angle β with respect to the normal N of the surface of the vibration element 30. iis incident on the diffraction grating 34, the blaze angle θ B Therefore, the reference light L2 returns at the same angle as the incident angle β. B By making it equal to the incident light K i of The condition that the angle between the incident direction and the traveling direction of the reference light L2 is 180° can be satisfied. In this case, the above condition can be satisfied without using the mirror 37 shown in Fig. 7 or without tilting the vibration element 30 itself as shown in Fig. 8, so the laser interferometer 1 can be made even more compact and operate at a higher frequency. In particular, in the case of a blazed diffraction grating, an arrangement that satisfies the above condition is called a "Littrow arrangement," which has the advantage of being able to particularly increase the diffraction efficiency of the diffracted light.

[0074] 9 indicates the pitch of the blazed diffraction grating, and as an example, the pitch P is set to 1 μm. B is set to, for example, 25°. In this case, in order to satisfy the above condition, the incident light K i The angle of incidence β with respect to the normal N should also be set to 25°.

[0075] Package Structure FIG. 10 is a cross-sectional view showing an optical modulator 12 having a package structure.

[0076] 10 includes a container 70 serving as a housing, an optical modulation oscillator 120 housed in the container 70, and a circuit element 45 constituting an oscillation circuit 54. The container 70 is hermetically sealed in a reduced pressure atmosphere such as a vacuum, or in an inert gas atmosphere such as nitrogen or argon.

[0077] 10, the container 70 has a container body 72 and a lid 74. Of these, the container body 72 has a first recess 721 provided therein and a second recess 722 provided inside the first recess 721 and deeper than the first recess 721. The container body 72 is made of, for example, a ceramic material, a resin material, or the like. Although not shown, the container body 72 also has internal terminals provided on the inner surface, external terminals provided on the outer surface, wiring connecting the internal terminals and the external terminals, and the like.

[0078] The opening of the container body 72 is closed by a lid 74 via a sealing member such as a seal ring or low-melting-point glass (not shown). The lid 74 is made of a material that is transparent to laser light, such as a glass material.

[0079] The optical modulation oscillator 120 is disposed on the bottom surface of the first recess 721. The optical modulation oscillator 120 is supported on the bottom surface of the first recess 721 by a bonding member (not shown). Furthermore, the internal terminal of the container body 72 and the optical modulation oscillator 120 are electrically connected via a conductive material (not shown), such as a bonding wire or a bonding metal.

[0080] The circuit element 45 is disposed on the bottom surface of the second recess 722. The circuit element 45 is electrically connected to an internal terminal of the container body 72 via a bonding wire 76. As a result, the optical modulation oscillator 120 and the circuit element 45 are also electrically connected via the wiring provided in the container body 72. Note that the circuit element 45 may be provided with a circuit other than the oscillation circuit 54 described below.

[0081] By adopting such a package structure, the optical modulation oscillator 120 and the circuit element 45 can be stacked, thereby reducing the physical distance between them and shortening the wiring length between them. This makes it possible to prevent external noise from entering the drive signal Sd, or conversely, to prevent the drive signal Sd from becoming a noise source. Furthermore, a single container 70 can protect both the optical modulation oscillator 120 and the circuit element 45 from the external environment. This makes it possible to reduce the size of the sensor head unit 51 while improving the reliability of the laser interferometer 1.

[0082] The structure of the container 70 is not limited to the structure shown in the figure, and for example, the optical modulation oscillator 120 and the circuit element 45 may have separate package structures. Although not shown, the container 70 may also house other circuit elements that make up the oscillation circuit 54. The container 70 may be provided as needed, and may be omitted.

[0083] 1.1.2. Current-to-voltage converter The current-voltage converter 531 is also called a transimpedance amplifier (TIA), and converts the photocurrent (received light signal) output from the light receiving element 10 into a voltage signal, which is output as a light detection signal.

[0084] 1 is disposed between the current-voltage converter 531 and the demodulation circuit 52. The ADC 532 is an analog-to-digital converter that converts an analog signal into a digital signal at a predetermined sampling bit rate. The ADC 532 is provided in the sensor head unit 51.

[0085] The optical system 50 may include a plurality of light receiving elements 10. In this case, by providing a differential amplifier circuit between the plurality of light receiving elements 10 and the current-voltage converter 531, it is possible to perform differential amplification processing on the photocurrent and increase the S / N ratio (signal-to-noise ratio) of the photodetection signal. Note that the differential amplification processing may also be performed on the voltage signal.

[0086] Oscillator Circuit 1, the oscillation circuit 54 outputs a drive signal Sd to be input to the optical modulator 12 of the optical system 50. The oscillation circuit 54 also outputs a reference signal Ss to be input to the demodulation circuit 52.

[0087] The oscillator circuit 54 is not particularly limited, and circuits of various configurations can be used as long as they are capable of oscillating the vibration element 30. As an example of the circuit configuration, a circuit diagram showing the configuration of a single-stage inverter oscillator circuit is shown in FIG.

[0088] The oscillation circuit 54 shown in FIG. 11 includes a circuit element 45, a feedback resistor Rf, a limiting resistor Rd, a first capacitor Cg, a second capacitor Cd, and a third capacitor C3.

[0089] The circuit element 45 is an inverter IC. The terminals X1 and X2 of the circuit element 45 are terminals connected to the inverters inside the circuit element 45. The terminal GND is connected to the ground potential, and the terminal Vcc is connected to the power supply potential. The terminal Y is a terminal for oscillation output.

[0090] A first capacitor Cg is connected between terminal X1 and ground potential. A limiting resistor Rd and a second capacitor Cd are connected in series between terminal X2 and ground potential, in that order from the terminal X2 side. Furthermore, one end of a feedback resistor Rf is connected between terminal X1 and the first capacitor Cg, and the other end of the feedback resistor Rf is connected between terminal X2 and limiting resistor Rd.

[0091] One end of the vibration element 30 is connected between the first capacitor Cg and the feedback resistor Rf, and the other end of the vibration element 30 is connected between the second capacitor Cd and the limiting resistor Rd. This makes the vibration element 30 a signal source for the oscillation circuit 54.

[0092] FIG. 12 is an example of a circuit diagram showing an LCR equivalent circuit of the vibration element 30. As shown in FIG. 12, the LCR equivalent circuit of the vibrating element 30 is made up of a series capacitance C1, a series inductance L1, an equivalent series resistance R1, and a parallel capacitance C0.

[0093] In the oscillation circuit 54 shown in FIG. 11, the capacitance of the first capacitor Cg is set to C g The capacitance of the second capacitor Cd is C d Then, the load capacitance C L is given by the following equation (a):

[0094]

number

[0095] Then, the oscillation frequency f output from the terminal Y of the oscillation circuit 54 is osc is expressed by the following formula ( b) is given by

[0096]

number

[0097] f Q is the natural frequency of the vibration element 30. According to the above formula (b), the load capacitance C L By appropriately changing the oscillation frequency f of the signal output from terminal Y, osc It can be seen that the

[0098] In addition, the natural frequency f of the vibration element 30 Q and the oscillation frequency f of the oscillator circuit 54 osc The difference between Δf is given by the following equation (c):

[0099]

number

[0100] where C1< <C0、C1<<C LTherefore, Δf can be approximately calculated by the following equation (d): Given.

[0101]

number

[0102] Therefore, the oscillation frequency f of the oscillator circuit 54 osc is the natural frequency f of the vibration element 30 Q to The value will depend on the

[0103] Here, when the vibration element 30 is fixed to, for example, the container 70, if it is subjected to expansion stress due to temperature via the fixing part, the natural frequency f Q Furthermore, when the vibration element 30 is tilted, the natural frequency f Q fluctuates.

[0104] For this reason, the oscillator circuit 54 has a natural frequency f Q Even if fluctuates, the oscillation frequency f osc will change. That is, the oscillation frequency f osc is always increased by Δf, and the natural frequency f Q This will result in a value that deviates from the This stabilizes the vibration and displacement amplitude of the vibration element 30. Stable displacement amplitude stabilizes the modulation characteristics of the optical modulator 12, thereby improving the demodulation accuracy of the sample signal in the demodulation circuit 52.

[0105] As an example, Δf = |f osc -f Q |≦3000 [Hz], and Δf It is more preferable that the frequency is ≦600 [Hz].

[0106] The laser interferometer 1 also includes a demodulation circuit 52 and an oscillation circuit 54. The demodulation circuit 52 demodulates a sample signal derived from the measurement object 14 from a light detection signal based on a photocurrent (received light signal) based on a reference signal Ss. The oscillation circuit 54 operates using the vibration element 30 as a signal source, and outputs the reference signal Ss to the demodulation circuit 52, as shown in FIG.

[0107] With this configuration, the natural frequency f Q Even if the oscillation frequency f of the oscillator circuit 54 fluctuates, osc The natural frequency f of the vibration element 30 Q The value can be changed according to the This allows the vibration of the vibration element 30 to be easily stabilized. This allows the temperature characteristics of the modulation signal to correspond to the temperature characteristics of the vibration element 30, thereby stabilizing the modulation characteristics of the optical modulator 12. As a result, the demodulation accuracy of the sample signal in the demodulation circuit 52 can be improved.

[0108] Furthermore, in the above configuration, the temperature characteristics of the reference signal Ss output from the oscillator circuit 54 to the demodulation circuit 52 can also be made to correspond to the temperature characteristics of the vibration element 30. In this way, both the temperature characteristics of the modulated signal and the temperature characteristics of the reference signal correspond to the temperature characteristics of the vibration element 30, so that the behavior of the fluctuations in the modulated signal and the behavior of the fluctuations in the reference signal Ss that accompany temperature changes match or are similar to each other. Therefore, even if the temperature of the vibration element 30 changes, the effect on demodulation accuracy can be suppressed, and the demodulation accuracy of the sample signal derived from the measurement object 14 can be improved.

[0109] Furthermore, since the power consumption of the oscillator circuit 54 is low, the power consumption of the laser interferometer 1 can be easily reduced.

[0110] As mentioned above, the vibrating element 30 is preferably a quartz crystal vibrator. This allows for the generation of a highly accurate modulated signal by utilizing the extremely high Q value of quartz crystal. As a result, the sample signal derived from the measurement object 14 can be acquired with high accuracy.

[0111] Instead of the oscillation circuit 54, a signal generator such as a function generator or a signal generator may be used.

[0112] 1.2.Main body The main body 59 shown in FIGS. 1 and 2 includes a demodulation circuit 52.

[0113] The demodulation circuit 52 performs a demodulation process to demodulate the light detection signal output from the current-voltage converter 531 into a sample signal derived from the measurement object 14. The sample signal includes, for example, phase information and frequency information. The displacement of the measurement object 14 can be obtained from the phase information, and the velocity of the measurement object 14 can be obtained from the frequency information. If different physical quantities can be obtained in this way, the laser interferometer 1 can be given the functions of a displacement meter and a speed meter, thereby improving the functionality of the laser interferometer 1.

[0114] The circuit configuration of the demodulation circuit 52 is set according to the modulation processing method. The laser interferometer 1 according to this embodiment uses an optical modulator 12 equipped with a vibration element 30. The vibration element 30 is an element that vibrates simply, and therefore the vibration speed changes from moment to moment within the period. For this reason, the modulation frequency also changes over time, and a conventional demodulation circuit cannot be used as is.

[0115] A conventional demodulation circuit refers to a circuit that demodulates a sample signal from an optical detection signal that includes a modulated signal modulated using, for example, an acousto-optic modulator (AOM). An acousto-optic modulator does not change its modulation frequency. Therefore, while a conventional demodulation circuit can demodulate a sample signal from an optical detection signal that includes a modulated signal whose modulation frequency does not change, it cannot directly demodulate a sample signal that includes a modulated signal modulated by an optical modulator 12 whose modulation frequency changes.

[0116] 1 includes a preprocessing unit 53 and a demodulation processing unit 55. The photodetection signal output from the current-voltage converter 531 first passes through the preprocessing unit 53 and is then guided to the demodulation processing unit 55. The preprocessing unit 53 performs preprocessing on the photodetection signal. This preprocessing allows a signal that can be demodulated by a conventional demodulation circuit to be obtained. Therefore, the demodulation processing unit 55 demodulates the sample signal derived from the measurement object 14 using a known demodulation method.

[0117] The above-mentioned functions of the demodulation circuit 52 are realized by hardware including, for example, a processor, memory, an external interface, an input unit, a display unit, etc. Specifically, the functions are realized by the processor reading and executing a program stored in the memory. These components are capable of communicating with each other via an internal bus.

[0118] Examples of processors include a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. Instead of using these processors to execute software, a system in which software is executed by an FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), etc. may be adopted.

[0119] Examples of memory include HDD (Hard Disk Drive), SSD (Solid State Drive), EEPROM (Electrically Erasable Programmable Read-Only Memory), ROM (Read-Only Memory), and RAM (Random Access Memory).

[0120] Examples of the external interface include a digital input / output port such as a USB (Universal Serial Bus), an Ethernet (registered trademark) port, and the like.

[0121] Examples of the input unit include various input devices such as a keyboard, a mouse, a touch panel, a touch pad, etc. Examples of the display unit include a liquid crystal display panel, an organic EL (Electro Luminescence) display panel, etc.

[0122] 1.2.1. Configuration of the preprocessing unit 1 includes a first band-pass filter 534, a second band-pass filter 535, a first delay adjuster 536, a second delay adjuster 537, a multiplier 538, a third band-pass filter 539, a first AGC 540, a second AGC 541, and an adder 542. Note that AGC is Auto Gain Control.

[0123] The photodetection signal output from the current-voltage converter 531 is split into two signals, a first signal S1 and a second signal S2, at the branch point jp1. In Fig. 1, the path of the first signal S1 is referred to as a first signal path ps1, and the path of the second signal S2 is referred to as a second signal path ps2.

[0124] The ADC 533 is connected between the oscillator circuit 54 and the second delay adjuster 537. The ADC 533 is an analog-to-digital converter that converts an analog signal into a digital signal at a predetermined sampling bit rate. The ADC 533 is provided in the sensor head unit 51.

[0125] First band-pass filter 534, second band-pass filter 535, and third band-pass filter 539 are filters that selectively transmit signals in specific frequency bands.

[0126] First delay adjuster 536 and second delay adjuster 537 are circuits that adjust the delay of a signal, multiplier 538 is a circuit that generates an output signal proportional to the product of two input signals, and adder 542 is a circuit that generates an output signal proportional to the sum of two input signals.

[0127] Next, the operation of the pre-processing unit 53 will be described along the flow of the first signal S1, the second signal S2, and the reference signal Ss.

[0128] The first signal S1 passes through a first band-pass filter 534 arranged on the first signal path ps1, and then the group delay is adjusted by a first delay adjuster 536. The group delay adjusted by the first delay adjuster 536 corresponds to the group delay of the second signal S2 caused by a second band-pass filter 535, which will be described later. This delay adjustment makes it possible to align the delay times associated with passing through the filter circuits between the first band-pass filter 534, through which the first signal S1 passes, and the second band-pass filter 535 and third band-pass filter 539, through which the second signal S2 passes. The first signal S1 that has passed through the first delay adjuster 536 passes through a first AGC 540 and is input to an adder 542.

[0129] The second signal S2 is passed through a second band-pass filter 535 arranged on the second signal path ps2, and then input to a multiplier 538. In the multiplier 538, the second signal S2 is multiplied by a reference signal Ss output from a second delay adjuster 537. Specifically, the cos(ω m The reference signal Ss represented by ωt is converted into a digital signal by the ADC 533, and its phase is adjusted by the second delay adjuster 537, and then input to the multiplier 538. m is the angular frequency of the modulated signal by the optical modulator 12, and t is time. After that, the second signal S2 passes through a third band-pass filter 539, then passes through a second AGC 541, and is input to an adder 542.

[0130] The adder 542 outputs an output signal proportional to the sum of the first signal S1 and the second signal S2. The above circuit configuration of the preprocessing unit 53 is an example and is not limited to this.

[0131] 1.2.2. Basic principles of pretreatment Next, the basic principle of preprocessing in the preprocessing unit 53 will be explained. In the following explanation, as an example, a system will be considered in which the frequency of the modulation signal changes sinusoidally and the displacement of the measurement object 14 also changes in simple harmonic motion in the optical axis direction. Here, E m , E d , φ,

[0132]

number

[0133] When this is the case, the light detection signal I output from the current-voltage converter 531 is PD is theoretically expressed as follows: is represented.

[0134]

number

[0135] In addition, E m , E d , φ m , φ d , φ, ω m , ω d ,ω0,a m , a d are respectively as follows: As follows.

[0136]

number

[0137] In addition, < > in equation (4) represents the time average. The first and second terms in the above equation (4) represent the DC component, and the third term represents the AC component. This AC component is called I PD·AC Then, I PD·AC is expressed as follows:

[0138]

number

[0139] Here, the v-order Bessel functions such as the following formulas (8) and (9) are known.

[0140]

number

[0141] When the above formula (5) is expanded into a series using the Bessel functions of the above formulas (8) and (9), it can be transformed into the following formula (10).

[0142]

number

[0143] where J0(B), J1(B), J2(B), ... are the Bessel coefficients. do.

[0144] By modifying it as described above, it can be said that, theoretically, it is possible to extract a band corresponding to a specific order using a band-pass filter.

[0145] Based on this theory, the pre-processing unit 53 performs pre-processing on the photodetection signal in the following manner.

[0146] First, the photodetection signal output from the current-voltage converter 531 is split into two signals, a first signal S1 and a second signal S2, at the branching point jp1. The first signal S1 is passed through a first band-pass filter 534. The first band-pass filter 534 has a center angular frequency of ω m As a result, the first signal S1 after passing through the first band-pass filter 534 is expressed by the following equation.

[0147]

number

[0148] On the other hand, the second signal S2 is passed through a second band-pass filter 535. The center angular frequency of the second band-pass filter 535 is set to a value different from the center angular frequency of the first band-pass filter 534. Here, as an example, the center angular frequency of the second band-pass filter 535 is set to 2ω m As a result, the second signal S2 after passing through the second band-pass filter 535 is expressed by the following equation.

[0149]

number

[0150] The second signal S2 after passing through the second band-pass filter 535 is multiplied by the reference signal Ss in the multiplier 538. The second signal S2 after passing through the multiplier 538 is expressed by the following equation.

[0151]

number

[0152] The second signal S2 after passing through the multiplier 538 is passed through a third band-pass filter 539. The central angular frequency of the third band-pass filter 539 is set to the same value as the central angular frequency of the first band-pass filter 534. Here, as an example, the central angular frequency of the third band-pass filter 539 is set to ω m As a result, the second signal S2 after passing through the third band-pass filter 539 is expressed by the following equation.

[0153]

number

[0154] Thereafter, the first signal S1 expressed by the above equation (11) is adjusted in phase by the first delay adjuster 536 and in amplitude by the first AGC 540.

[0155] The amplitude of the second signal S2 expressed by the above equation (14) is also adjusted by the second AGC 541, so that the amplitude of the second signal S2 is made equal to the amplitude of the first signal S1.

[0156] Then, the first signal S1 and the second signal S2 are added together in the adder 542. The result of the addition is expressed by the following equation (15).

[0157]

number

[0158] As shown in the above equation (15), the unnecessary terms disappear as a result of the addition, and the necessary terms can be extracted. In other words, the addition result I 53 is a signal obtained by extracting frequency modulation components. This addition result is I 53 is input to the demodulation processing unit 55.

[0159] 1.2.3. Demodulation Processing Unit Configuration The demodulation processing unit 55 performs demodulation processing to demodulate the signal output from the preprocessing unit 53 into a sample signal originating from the measurement object 14. The demodulation processing is not particularly limited, but may be a well-known quadrature detection method. The quadrature detection method is a method of performing demodulation processing by externally mixing mutually orthogonal signals with respect to the input signal.

[0160] The demodulation processing unit 55 shown in FIG. 1 is a digital circuit including 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 calculator 558, and an output circuit 559.

[0161] Multipliers 551 and 552 are circuits that generate an output signal proportional to the product of two input signals. Phase shifter 553 is a circuit that generates an output signal by inverting the phase of the input signal without changing the amplitude. First low-pass filter 555 and second low-pass filter 556 are filters that cut signals in high frequency bands.

[0162] The divider 557 is a circuit that generates an output signal proportional to the quotient of two input signals. The arctangent calculator 558 is a circuit that outputs the arctangent of the input signal. The output circuit 559 calculates the phase φ as information derived from the object 14 to be measured from the phase φ acquired by the arctangent calculator 558. d Furthermore, the output circuit 559 performs phase unwrapping when there is a phase jump of 2π between two adjacent points by phase unwrapping. Then, the displacement of the object 14 to be measured is calculated from the obtained phase information. This realizes a displacement meter. Furthermore, the velocity of the object 14 to be measured can be obtained from the displacement. This realizes a speed meter.

[0163] The above-described circuit configuration of the demodulation processing unit 55 is merely an example and is not limiting. For example, the demodulation processing unit 55 is not limited to a digital circuit and may be an analog circuit. The analog circuit may include an F / V converter circuit and a ΔΣ counter circuit.

[0164] 1.2.4. Demodulation processing by the demodulation processing unit In the demodulation process, first, the signal output from the pre-processing unit 53 is split into two by the branching unit jp2. One of the split signals is multiplied by the multiplier 551 using cos(ω m The other signal after division is multiplied by a reference signal Ss expressed as -sin(ω m The reference signal Ss and the signal obtained by shifting the phase of the reference signal Ss are signals whose phases are shifted by 90° from each other.

[0165] The signal that has passed through multiplier 551 passes through first low-pass filter 555 and is then input as signal x to divider 557. The signal that has passed through multiplier 552 passes through second low-pass filter 556 and is then input as signal y to divider 557. Divider 557 divides signal y by signal x, and passes the output y / x through arctangent calculator 558 to obtain output atan(y / x).

[0166] Thereafter, the output atan(y / x) is passed through the output circuit 559 to output the phase φ as information derived from the object 14 to be measured. d is obtained. In the output circuit 559, phase unwrapping is performed when there is a phase jump of 2π between adjacent points. Then, the displacement of the measurement object 14 can be calculated from the phase information. This realizes a displacement meter. Furthermore, the velocity can be obtained from the displacement. This realizes a speed meter.

[0167] On the other hand, frequency information may be obtained in the output circuit 559. Based on the frequency information, the velocity of the object 14 to be measured can be calculated.

[0168] 1.3. Advantages of the First Embodiment As described above, the laser interferometer 1 according to the first embodiment includes a laser light 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).

[0169] The laser light source 2 emits an output light L1 (first laser light). The optical modulator 12 includes a vibration element 30 and modulates the output light L1 using the vibration element 30 to generate a reference light L2 (second laser light) containing a modulation signal. The light-receiving element 10 receives the reference light L2 and an object light L3 (third laser light) containing a sample signal generated when the output light L1 is reflected by a measurement object 14, and outputs a received light signal. The optical coupler 4 receives the output light L1, the reference light L2, and the object light L3, and has the function of splitting the output light L1 and the function of splitting a combined light L4 of the reference light L2 and the object light L3. The collimator 21 (first collimator) collimates one of the output light L1 split by the optical coupler 4 and outputs it toward the optical modulator 12. The collimator 22 (second collimator) collimates the other outgoing light L1 branched by the optical coupler 4, and emits the collimated light toward the object 14 to be measured.

[0170] The optical fiber 61 optically connects the laser light source 2 and the optical coupler 4, and causes the output light L1 emitted from the laser light source 2 to be incident on the optical coupler 4. The optical fiber 62 optically connects the light receiving element 10 and the optical coupler 4, and causes the combined light L4 branched by the optical coupler 4 to be incident on the light receiving element 10. The optical fiber 63 optically connects the collimator 21 and the optical coupler 4. The optical fiber 64 optically connects the collimator 22 and the optical coupler 4.

[0171] According to this configuration, optical elements such as the laser light source 2, the optical coupler 4, the light-receiving element 10, the collimator 21, the optical modulator 12, and the collimator 22 are connected to one another using optical fibers 61-64, which are optical wiring. This reduces the number of connections through which light propagates in free space. This facilitates alignment of the optical system 50 and reduces the need for realignment. Furthermore, while there are limitations on the miniaturization of optical elements at connection points requiring alignment, the optical system 50 obviates such limitations and eliminates the need for position adjustment devices and other devices required for alignment. This facilitates the miniaturization and weight reduction of the optical system 50. Furthermore, the optical fibers 61-64 are flexible, allowing light to propagate even when bent. This allows for optimal placement of optical elements, making it easier to reduce the space required for the optical system 50.

[0172] In this embodiment, the optical coupler 4 is an optical fiber coupler, and the first optical wiring, the second optical wiring, the third optical wiring, and the fourth optical wiring are the optical fibers 61 to 64 as described above.

[0173] According to this configuration, the optical fiber coupler is formed by fusing optical fibers together, thereby realizing a structure in which the optical coupler 4 and the optical fibers 61 to 64 are integrated together, thereby realizing an optical system 50 with little optical loss.

[0174] Moreover, the laser interferometer 1 according to this embodiment has a movable sensor head unit 51 and a main body unit 59. 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 provided in the sensor head unit 51. "Provided in the sensor head unit 51" means that these optical elements are housed in a housing (not shown) of the sensor head unit 51 or attached to the outside of the housing.

[0175] With this configuration, only the electrical wiring (not shown) electrically connecting the sensor head 51 and the main body 59 is exposed to the outside space, while all of the optical fibers 61-64 are provided in the sensor head 51. This prevents the optical fibers 61-64 from being exposed to the outside space, and suppresses the influence of external disturbances on the optical signals propagating through the optical fibers 61-64. Examples of the influence of external disturbances include unintended changes in the optical signals due to vibration, expansion, contraction, temperature changes, etc. of the optical fibers 61-64. By suppressing the influence of such disturbances, the S / N ratio of the received light signal output from the light-receiving element 10 can be improved. As a result, the measurement accuracy of the displacement and velocity of the measurement object 14 that can be measured using the laser interferometer 1 can be improved.

[0176] The laser interferometer 1 according to this embodiment also includes a demodulation circuit 52 and an oscillation circuit 54. The oscillation circuit 54 operates using the vibration element 30 as a signal source, and outputs a reference signal Ss to the demodulation circuit 52, as shown in Fig. 1. The demodulation circuit 52 demodulates a sample signal derived from the measurement object 14 from the received light signal based on the reference signal Ss.

[0177] With this configuration, the natural frequency f Q Even if the oscillation frequency f of the oscillator circuit 54 fluctuates, osc The natural frequency f of the vibration element 30 Q The value can be changed according to the This allows the vibration of the vibration element 30 to be easily stabilized. This allows the temperature characteristics of the modulation signal to correspond to the temperature characteristics of the vibration element 30, thereby stabilizing the modulation characteristics of the optical modulator 12. As a result, the demodulation accuracy of the sample signal in the demodulation circuit 52 can be improved.

[0178] Furthermore, in the above configuration, the temperature characteristics of the reference signal Ss output from the oscillator circuit 54 to the demodulation circuit 52 can also be made to correspond to the temperature characteristics of the vibration element 30. In this way, both the temperature characteristics of the modulated signal and the temperature characteristics of the reference signal correspond to the temperature characteristics of the vibration element 30, so that the behavior of the fluctuations in the modulated signal and the behavior of the fluctuations in the reference signal Ss that accompany temperature changes match or are similar to each other. Therefore, even if the temperature of the vibration element 30 changes, the effect on demodulation accuracy can be suppressed, and the demodulation accuracy of the sample signal derived from the measurement object 14 can be improved.

[0179] Furthermore, since the oscillator circuit 54 consumes less power than a function generator, a signal generator, or the like, it is easy to achieve power saving in the laser interferometer 1.

[0180] 1.4. First Modification of the First Embodiment Next, a first modification of the first embodiment will be described.

[0181] FIG. 13 is a perspective view showing a sensor head unit 51 of a laser interferometer 1A according to a first modified example of the first embodiment.

[0182] The first modified example will be described below, focusing on the differences from the first embodiment, and omitting a description of similarities. Note that in Fig. 13, the same reference numerals are used to designate the same components as those in the first embodiment.

[0183] The laser interferometer 1A according to the first modification further includes a mounting substrate 9 provided on the sensor head unit 51. 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 mounted on the mounting substrate 9, as shown in FIG.

[0184] According to this configuration, the optical elements can be fixed to the mounting substrate 9, so that the sensor head unit 51 can be further reduced in size and made easier to handle. This configuration also contributes to improved durability against disturbances such as vibrations, shocks, and temperature changes.

[0185] Examples of the mounting substrate 9 include a resin substrate, a ceramic substrate, and a metal substrate. The mounting substrate 9 may also be a circuit board. A circuit board is a substrate with built-in electrical wiring. This allows some of the electrical wiring that electrically connects the laser light source 2, the light receiving element 10, and the optical modulator 12 to the main body 59 to be built into the circuit board. This allows the sensor head 51 to be further miniaturized and easier to manufacture.

[0186] Furthermore, similar to the first embodiment described above, the first modified example also provides a high degree of freedom in the arrangement of the laser light source 2, the light receiving element 10, and the optical modulator 12. Therefore, the arrangement of each can be optimized taking into account the mutual influence of electromagnetic noise generated from each of these components.

[0187] It is preferable that the optical coupler 4 is fixed to the mounting substrate 9 at two or more points. This makes it possible to prevent the optical coupler 4 from being affected by vibrations or shocks even if the sensor head unit 51 is subjected to such vibrations or shocks.

[0188] The collimators 21 and 22 may be fixed on the surface of the mounting substrate 9, or may be fitted into a recess or a through-hole provided in the mounting substrate 9 and fixed thereto. In the first modified example as described above, the same effects as in the first embodiment can be obtained.

[0189] 1.5. Second Modification of the First Embodiment Next, a second modification of the first embodiment will be described.

[0190] FIG. 14 is a schematic diagram showing the configuration of a sensor head unit 51 of a laser interferometer 1B according to a second modified example of the first embodiment.

[0191] The second modified example will be described below, focusing on the differences from the first embodiment, and omitting a description of similarities. Note that in Fig. 14, the same reference numerals are used to designate the same components as those in the first embodiment.

[0192] As shown in FIG. 14, a laser interferometer 1B according to the second modification is similar to the laser interferometer 1 according to the first embodiment, except that it includes a collimator 23 (third collimator).

[0193] 14 is provided between the laser light source 2 and the optical coupler 4, and collimates the emitted light L1 (first laser light). The collimator 23 is an optical element (optical component) disposed between the laser light source 2 and the optical coupler 4, and an example of the optical element is an aspherical lens. The emitted light L1 emitted from the laser light source 2 passes through the collimator 23 and enters the optical fiber 61.

[0194] By providing such a collimator 23, it is possible to increase the efficiency of incidence of the output light L1 onto the optical fiber 61. In other words, it is possible to suppress the coupling loss between the laser light source 2 and the optical fiber 61.

[0195] The collimator 23 may include an optical element other than an aspherical lens. In the second modified example as described above, the same effects as in the first embodiment can be obtained.

[0196] 2. Second embodiment Next, a laser interferometer according to a second embodiment will be described.

[0197] FIG. 15 is a schematic diagram showing the configuration of a sensor head unit 51 of a laser interferometer 1C according to the second embodiment.

[0198] The second embodiment will be described below, focusing on the differences from the first embodiment, and the description of the similarities will be omitted. Note that in Fig. 15, the same reference numerals are used to designate the same components as those in the first embodiment.

[0199] 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 provided in the sensor head unit 51.

[0200] 15, the laser interferometer 1C according to this embodiment has a movable sensor head unit 51 and a main body unit 59, and a collimator 22 (second collimator) is provided in the sensor head unit 51. Meanwhile, the laser light source 2, the optical modulator 12, the light receiving element 10, the optical coupler 4, and the collimator 21 (first collimator) are provided in the main body unit 59. "Provided in the main body unit 59" means that these optical elements are housed in a housing (not shown) of the main body unit 59 or attached to the outside of the housing.

[0201] According to this configuration, it is possible to reduce the number of optical elements provided in the sensor head unit 51 compared to the first embodiment, thereby making it possible to particularly reduce the size of the sensor head unit 51. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0202] 3. Third embodiment Next, a laser interferometer according to a third embodiment will be described.

[0203] FIG. 16 is a schematic diagram showing the configuration of a sensor head unit 51 of a laser interferometer 1D according to the third embodiment.

[0204] The third embodiment will be described below, focusing on the differences from the first embodiment, and omitting a description of similarities. Note that in Fig. 16, the same reference numerals are used to designate the same components as those in the first embodiment.

[0205] 16, the laser interferometer 1D according to this embodiment has a movable sensor head unit 51 and a main body unit 59, and the optical modulator 12, the collimator 21 (first collimator), and the collimator 22 (second collimator) are provided in the sensor head unit 51. On the other hand, the laser light source 2, the light receiving element 10, and the optical coupler 4 are provided in the main body unit 59.

[0206] With this configuration, the collimators 21 and 22 are provided in the sensor head 51, and the optical coupler 4 is provided in the main body 59. Therefore, optical fibers 63 and 64 are routed between the sensor head 51 and the main body 59. The optical fiber 63 optically connects the collimator 21 and the optical coupler 4 and is the medium through which the reference light L2 propagates. The optical fiber 64 optically connects the collimator 22 and the optical coupler 4 and is the medium through which the object light L3 propagates. Because both the optical fibers 63 and 64 are routed externally, both the reference light L2 and the object light L3 are affected by disturbances. This allows the influence of disturbances on the reference light L2 and the object light L3 to be canceled out or suppressed. As a result, the S / N ratio of the received light signal can be increased or stabilized.

[0207] Furthermore, in this embodiment, the number of optical elements provided in the sensor head unit 51 can be reduced compared to the first embodiment, thereby making it possible to reduce the size of the sensor head unit 51. In the third embodiment as described above, the same effects as in the first embodiment can be obtained.

[0208] 4. Fourth embodiment Next, a laser interferometer according to a fourth embodiment will be described.

[0209] FIG. 17 is a schematic diagram showing the configuration of a sensor head unit 51 of a laser interferometer 1E according to the fourth embodiment.

[0210] The fourth embodiment will be described below, focusing on the differences from the first embodiment, and omitting a description of similarities. Note that in Fig. 17, the same reference numerals are used to designate the same components as those in the first embodiment.

[0211] 17, the laser interferometer 1E according to this embodiment is similar to the laser interferometer 1 according to the first embodiment except that it has an optical isolator 5 provided between the laser light source 2 and the optical coupler 4. The optical isolator 5 has the function of reducing return light L5 from the optical coupler 4 toward the laser light source 2.

[0212] Here, the optical coupler 4 is a 2x2 type coupler. Therefore, one of the branched combined light beams L4 is incident on the light receiving element 10, while the other branched combined light beam L4 is directed toward the laser light source 2. The light directed from the optical coupler 4 toward the laser light source 2 is called "return light L5." When the return light L5 is incident on the laser light source 2, the laser oscillation in the laser light source 2 becomes unstable. The instability of the laser oscillation causes a decrease in the S / N ratio of the received light signal.

[0213] Therefore, as described above, the laser interferometer 1E according to this embodiment includes the optical isolator 5. The optical isolator 5 is provided between the laser light source 2 and the optical coupler 4, and reduces the return light L5 traveling from the optical coupler 4 toward the laser light source 2.

[0214] This configuration can reduce the light intensity of the return light L5 incident on the laser light source 2. This can stabilize the laser oscillation in the laser light source 2. As a result, the phase of the emitted light L1 is also stabilized, which can increase the S / N ratio of the received light signal.

[0215] The principle of the optical isolator 5 may be, for example, a polarization-dependent type or a polarization-independent type, etc. The form of the optical isolator 5 may be, for example, a free space type or a direct fiber coupling type, etc.

[0216] Furthermore, the performance required of the optical isolator 5 can be expressed, for example, by the optical density (OD value) of the ability of the optical isolator 5 to block the return light L5. It is preferable that the ability of the optical isolator 5 to block the return light L5 satisfies OD≧4. This allows for sufficient stabilization of laser oscillation. In the fourth embodiment as described above, the same effects as in the first embodiment can be obtained.

[0217] 5. Fifth embodiment Next, a laser interferometer according to a fifth embodiment will be described.

[0218] FIG. 18 is a schematic diagram showing the configuration of a sensor head unit 51 of a laser interferometer 1F according to the fifth embodiment.

[0219] The fifth embodiment will be described below, focusing on the differences from the first embodiment, and omitting a description of similarities. Note that in Fig. 18, the same reference numerals are used to designate the same components as those in the first embodiment.

[0220] The laser interferometer 1F according to this embodiment is similar to the laser interferometer 1 according to the first embodiment except that, in addition to having the same configuration as the laser interferometer 1 according to the first embodiment described above, it is equipped with an optical path length changing unit 15 as shown in Fig. 18. The optical path length changing unit 15 has a function of changing the optical path length of the optical path along which the output light L1 emitted from the collimator 21 propagates.

[0221] Here, in order to increase the S / N ratio of the received light signal, it is necessary to suppress frequency fluctuations of the output light L1 emitted from the laser light source 2, i.e., fluctuations in the phase of the output light L1. However, the frequency fluctuations of the output light L1 depend on the type of laser light source 2 and are therefore not easy to suppress. Therefore, in this embodiment, by providing an optical path length changing unit 15, it is possible to suppress a decrease in the S / N ratio of the received light signal due to frequency fluctuations of the output light L1, and ultimately to improve the measurement accuracy of the displacement of the measurement object 14. The function of such an optical path length changing unit 15 will be described below.

[0222] The demodulation circuit 52 demodulates the received light signal into a sample signal derived from the measurement object 14. Then, the displacement of the measurement object 14 can be obtained from the sample signal. When the measurement accuracy of this displacement is Δd, the measurement accuracy Δd is expressed by the following formula (I).

[0223]

number

[0224] The measurement accuracy Δd is expressed by the above formula (I), which includes a first term including the wavelength λ, a second term including the optical path difference d and the frequency fluctuation Δf (phase fluctuation) of the emitted light L1, and a third term including the optical path difference d and the fluctuation Δn of the refractive index of the atmosphere. In formula (I), when the optical path difference d is 0, the second and third terms on the right-hand side also become 0. In this case, theoretically, the displacement measurement accuracy Δd is not affected 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 and the fluctuation Δn of the refractive index of the atmosphere affect the displacement measurement accuracy Δd. In particular, the frequency fluctuation Δf of the emitted light L1 may be relatively large depending on the type of laser light source 2. This raises concerns that the measurement accuracy Δd of the displacement of the measurement object 14 may deteriorate depending on the type of laser light source 2.

[0225] Therefore, in this embodiment, the optical path length changing unit 15 is operated so that the optical path difference d approaches 0, that is, so that the optical path length from point A to point B2 and the optical path length from point A to point C2 in FIG. 18 approach each other. The optical path length changing unit 15 has a function of changing the optical path length from point A to point B2. By making the optical path difference d approach 0, the displacement measurement accuracy Δd becomes less susceptible to the influence of the frequency fluctuation Δf [Hz] of the emitted light L1. As a result, the displacement of the measurement object 14 can be measured with high accuracy regardless of the type of laser light source 2. Furthermore, the velocity of the measurement object 14 can also be calculated from the displacement. Note that the optical path length refers to an optical distance. Also, point A in Figure 18 is the center of the optical coupler 4, point B1 is the connection point between the optical fiber 63 and the collimator 21, point B2 is the light reflection point of the optical modulator 12, point C1 is the connection point between the optical fiber 64 and the collimator 22, and point C2 is the light reflection point of the object to be measured 14.

[0226] 18 includes a first reflecting element 151, a second reflecting element 152, and a driving unit 153 that drives the first reflecting element 151. The first reflecting element 151 and the second reflecting element 152 are optical elements that switch the optical path 20 along which the output light L1 travels. The driving unit 153 moves the first reflecting element 151 to change the physical distance between the first reflecting element 151 and the second reflecting element 152. This changes the optical path length between point A and point B2.

[0227] The driving unit 153 generates a driving force to move the first reflecting element 151 in a direction connecting the first reflecting element 151 and the second reflecting element 152. The driving unit 153 also holds the first reflecting element 151 at a target position. The driving unit 153 may be configured to move the second reflecting element 152 instead of the first reflecting element 151, or may be configured to move both the first reflecting element 151 and the second reflecting element 152. The direction of movement is not important as long as the optical path length of the optical path 20 can be changed.

[0228] As the driving section 153, a device that moves the first reflecting element 151 along a straight line is used, and examples thereof include a linear stage, an electric actuator, and a piezoelectric actuator.

[0229] First reflecting element 151 shown in FIG. 18 includes right-angle prism mirrors 154a and 154b and a base material 156 that supports them. Right-angle prism mirrors 154a and 154b are optical elements each having a light-reflecting surface 150 that intersects with optical path 20 at an angle of 45°. Right-angle prism mirrors 154a and 154b are arranged so that the angle between their light-reflecting surfaces 150 is 90°. As a result, optical path 20 is folded back at the unit consisting of a pair of right-angle prism mirrors 154a and 154b, and directed toward second reflecting element 152. Base material 156 supports multiple pairs of right-angle prism mirrors 154a and 154b together.

[0230] Second reflecting element 152 shown in FIG. 18 includes right-angle prism mirrors 155a and 155b and a base material 157 that supports them. Right-angle prism mirrors 155a and 155b are optical elements each having a light-reflecting surface 150 that intersects with optical path 20 at an angle of 45°. Right-angle prism mirrors 155a and 155b are arranged so that the angle between their light-reflecting surfaces 150 is 90°. As a result, optical path 20 extending from first reflecting element 151 is turned back at the unit consisting of a pair of right-angle prism mirrors 155a and 155b, and returns to first reflecting element 151. Base material 157 supports multiple pairs of right-angle prism mirrors 155a and 155b together.

[0231] The right-angle prism mirrors 154a, 154b, 155a, and 155b are highly accurate and easily available, making them useful as optical elements for the first reflecting element 151 and the second reflecting element 152.

[0232] The configuration of the optical path length changing unit 15 is not limited to the above, 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 mirror, the route of the optical path 20, etc. may be different from those described above. Also, a roof prism mirror or an integrated prism mirror may be used instead of the above units.

[0233] As described above, the laser interferometer 1F according to this embodiment further includes the optical path length changing unit 15. The optical path length changing unit 15 is provided between the collimator 21 (first collimator) and the optical modulator 12, and changes the optical path length of the optical path 20 along which the output light L1 (first laser light) emitted from the collimator 21 propagates.

[0234] With this configuration, the optical path length of the optical path 20 can be freely changed, and the optical path difference d in the above formula (I) can be made close to 0, and preferably 0. This makes the displacement measurement accuracy Δd less susceptible to the influence of the frequency fluctuation Δf of the emitted light L1. As a result, regardless of the type of laser light source 2, the displacement of the measurement object 14 can be measured with high accuracy.

[0235] Among the above-mentioned laser light sources 2, VCSELs (vertical-cavity surface-emitting laser diodes) and FP-LDs (Fabry-Perot semiconductor laser diodes) are inexpensive, although the frequency fluctuation Δf of the emitted light L1 is relatively large. Therefore, by using these as the laser light source 2, it is possible to reduce the cost of the laser interferometer 1F.

[0236] 18 is adjusted taking into account the physical distance between optical elements and the refractive index of the atmosphere. In other words, when the optical path difference d is 0 in this embodiment, the following formula (II) holds true:

[0237]

number

[0238] The optical path length of the optical path 20 is adjusted using a standard sample whose vibration displacement or velocity is known. Specifically, the displacement or velocity of the standard sample is measured, and the driving unit 153 is operated so that the measured value approaches the known value. Then, when the measured value closest to the known value is obtained, the operation of the driving unit 153 is stopped, and measurement of the measurement object 14 is performed in that state.

[0239] 18 has the first reflecting element 151, which is a movable optical element, and the driving unit 153. The first reflecting element 151 has a function of changing the optical path length of the optical path 20, that is, the optical path length of the optical path 20 along which the emitted light L1 (first laser light) emitted from the collimator 21 (first collimator) propagates, by moving.

[0240] With this optical path length changing unit 15, it is possible to easily match the movement distance of the first reflecting element 151 by the driving unit 153 with the change amount of the optical path length of the optical path 20. This makes it possible to realize an optical path length changing unit 15 that can easily adjust the optical path length. Furthermore, actuators that can be used as the driving unit 153 are easy to obtain and have high accuracy in adjusting the amount of movement. Therefore, with the optical path length changing unit 15 configured as above, it is possible to adjust the optical path length with high accuracy. In the fifth embodiment as described above, the same effects as in the first embodiment can be obtained.

[0241] 6. Sixth embodiment Next, a laser interferometer according to a sixth embodiment will be described.

[0242] FIG. 19 is a schematic diagram showing the configuration of a sensor head unit 51 of a laser interferometer 1G according to the sixth embodiment.

[0243] The sixth embodiment will be described below, focusing on the differences from the fifth embodiment, and a description of similarities will be omitted. Note that in Fig. 19, the same reference numerals are used to designate the same components as those in the fifth embodiment.

[0244] 19, the laser interferometer 1G according to this embodiment is the same as the laser interferometer 1F according to the fifth embodiment except for the configuration of the optical path length changing unit 15G. The optical path length changing unit 15G has a function of changing the optical path length of the optical path along which the output light L1 emitted from the collimator 21 propagates.

[0245] In the laser interferometer 1F according to the fifth embodiment described above, the optical path length changing section 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 shown in FIG. 19 , the optical path length changing section 15G has a refractive index variable body 171 and an input section 172. The refractive index variable body 171 is disposed in the optical path 20 along which the output light L1 travels, and is a medium whose refractive index changes in response to an input control signal. The input section 172 inputs a control signal to the refractive index variable body 171.

[0246] In such an optical path length changing section 15 G, the optical path 20 passes through the refractive index variable body 171 . By changing the refractive index of the refractive index variable body 171, the optical path length of the optical path 20 can be changed.

[0247] The refractive index variable body 171 is a light-transmitting medium disposed on the optical path 20, and its refractive index changes when, for example, an electric field, a magnetic field, heat, or light is input as a control parameter. Among these, a polymer-dispersed liquid crystal is known as a medium using an electric field as a control parameter. The refractive index of a polymer-dispersed liquid crystal changes depending on the magnitude of the applied electric field. By using a polymer-dispersed liquid crystal as the refractive index variable body 171, the refractive index can be changed using an easily controllable electric field as a control parameter. This further simplifies the configuration of the optical path length changing unit 15G.

[0248] An example of the refractive index variable body 171 other than the polymer dispersed liquid crystal is a medium whose refractive index is temperature dependent. Examples of such a medium 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, and examples of such a heat exchange element include a Peltier element.

[0249] As described above, in the laser interferometer 1G according to this embodiment, the optical path length changing unit 15G shown in Fig. 19 has the refractive index variable body 171 and the input unit 172. The refractive index of the refractive index variable body 171 changes in response to an input of a control signal. The input unit 172 inputs the control signal to the refractive index variable body 171.

[0250] Such an optical path length changing unit 15G has no moving parts and is therefore highly durable, which can improve the reliability of the laser interferometer 1G.

[0251] 19 is adjusted taking into account the physical distance between optical elements and the refractive index of the atmosphere. That is, in this embodiment, when the optical path difference d is 0, the following formula (III) holds. Note that point B3 in FIG. 19 is the end of the refractive index variable body 171 on the point B1 side, and point B4 is the end of the refractive index variable body 171 on the point B2 side.

[0252]

number

[0253] The optical path length of the optical path 20 is adjusted using a standard sample with a known displacement or velocity of vibration. Specifically, the displacement or velocity of the standard sample is measured, and the input unit 172 is operated so that the measured value approaches the known value. Then, when the measured value closest to the known value is obtained, the operation of the input unit 172 is stopped, and measurement of the measurement object 14 is performed in that state. In the sixth embodiment as described above, the same effects as in the first embodiment can be obtained.

[0254] While the laser interferometer of the present invention has been described above based on the illustrated embodiment, the laser interferometer of the present invention is not limited to the embodiment, and the configuration of each part can be replaced with any configuration having a similar function. Furthermore, any other component may be added to the laser interferometer according to the embodiment.

[0255] Furthermore, the laser interferometer of the present invention may be a combination of any two or more of the above-described embodiments and modifications. For example, it may be a combination (first composite embodiment) of the fourth embodiment including an optical isolator and the fifth embodiment including a movable optical element, or a combination (second composite embodiment) of the fourth embodiment and the sixth embodiment including a refractive index variable body. Furthermore, 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 based on the first embodiment, but may also be based on the second or third embodiment.

[0256] In addition to the displacement meters and speed meters described above, the laser interferometer of the present invention can also be applied to, for example, vibrometers, inclinometers, distance meters (length measuring devices), etc. Applications of the laser interferometer of the present invention include optical comb interferometry technology that enables distance measurement, 3D imaging, spectroscopy, etc., and optical fiber gyros that realize angular velocity sensors, acceleration sensors, angular acceleration sensors, etc.

[0257] Furthermore, although the above-described embodiments and modifications have a so-called Michelson type interference optical system, the laser interferometer of the present invention can also be applied to other types of interference optical system, such as those having a Mach-Zehnder type interference optical system. [Explanation of symbols]

[0258] 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 light source, 4...optical coupler, 5...optical isolator, 9...mounting substrate, 10...light receiving element, 12...optical modulator, 14...measurement object, 15...optical path length changing section, 15G...optical path length changing section, 20...optical path, 21...collimator, 22...collimator, 23...collimator, 30...vibration element, 30A...vibration element, 30B...vibration element, 31...base Plate, 32...groove, 33...pad, 34...diffraction grating, 35...pad, 36...vibration direction, 37...mirror, 45...circuit element, 50...optical system, 51...sensor head unit, 52...demodulation circuit, 53...preprocessing unit, 54...oscillating circuit, 55...demodulation processing unit, 59...main body unit, 61...optical fiber, 62...optical fiber, 63...optical fiber, 64...optical fiber, 70...container, 72...container body, 74...lid, 76...bonding wire, 120...light modulation oscillator, 150...light reflecting surface, 151...first reflecting element, 152...second reflecting element, 153...driver , 154a...Right-angle prism mirror, 154b...Right-angle prism mirror, 155a...Right-angle prism mirror, 155b...Right-angle prism mirror, 156...Base material, 157...Base material, 171...Refractive index variable body, 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...Front surface, 312...Back surface, 531...Current-voltage converter, 532...ADC, 533...ADC, 534...First band-pass filter, 535...Second band-pass filter, 536...First delay delay adjuster, 537...second delay adjuster, 538...multiplier, 539...third band-pass filter, 540...first AGC, 541...second AGC, 542...adder, 551...multiplier, 552...multiplier, 553...phase shifter, 555...first low-pass filter, 556...second low-pass filter, 557...divider, 558...arctangent calculator, 559...output circuit, 721...first recess, 722...second recess, C0...shunt capacitance, C1...series capacitance, C3...third capacitor, Cd...second capacitor, Cg...first capacitor, GND...GND terminal, K -2s ...diffracted light, K -1s ...diffracted light, K 0s ...diffracted light, K 1s ...diffracted light, K 2s ...diffracted light, K i …Incoming 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 resistor, Rf...feedback resistor, S1...first signal, S2...second signal, Sd...drive signal, Ss...reference signal, Vcc...terminal, X1...terminal, X2...terminal, Y...terminal, jp1...branch, jp2...branch, ps1...first signal path, ps2...second signal path, x...signal x, y...signal y, β...angle of incidence, θ B …blaze angle, θ S ...angle of inclination degree

Claims

1. a laser light source that emits a first laser beam; an optical modulator including a vibration element, the optical modulator modulating the first laser light by using the vibration element to generate a second laser light including a modulation signal; a light-receiving element that receives the second laser light and a third laser light including a sample signal generated by reflection of the first laser light from a measurement object, and outputs a light-receiving signal; an optical coupler into which the first laser light, the second laser light, and the third laser light are incident, the optical coupler having 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 collimates one of the first laser beams branched by the optical coupler and emits the collimated first laser beam toward the optical modulator; a second collimator that collimates the other of the first laser beams branched by the optical coupler and emits the collimated laser beam toward the object to be measured; a first optical wiring that optically connects the laser light source and the optical coupler and causes the first laser light emitted from the laser light source to be incident on the optical coupler; a second optical wiring that optically connects the light receiving element and the optical coupler and causes the combined light branched by the optical coupler to be incident on the light receiving element; a third optical wiring that optically connects the first collimator and the optical coupler; a fourth optical wiring that optically connects the second collimator and the optical coupler; A laser interferometer comprising:

2. the optical coupler is an optical fiber coupler, 2. The laser interferometer according to claim 1, wherein the first optical wiring, the second optical wiring, the third optical wiring, and the fourth optical wiring are optical fibers.

3. A movable sensor head, a main body; and 3. The laser interferometer according to claim 1, wherein the laser light source, the optical modulator, the light receiving element, the optical coupler, the first collimator, and the second collimator are provided in the sensor head portion.

4. a mounting substrate provided on the sensor head portion, 4. The laser interferometer according to claim 3, wherein the laser light 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. A movable sensor head, a main body; and the second collimator is provided in the sensor head portion, 3. The laser interferometer according to claim 1, wherein the laser light source, the optical modulator, the light receiving element, the optical coupler, and the first collimator are provided in the main body.

6. A movable sensor head, a main body; and the optical modulator, the first collimator, and the second collimator are provided in the sensor head unit, 3. The laser interferometer according to claim 1, wherein the laser light source, the light receiving element, and the optical coupler are provided in the main body.

7. 7. The laser interferometer according to claim 1, further comprising an optical isolator provided between the laser light source and the optical coupler to reduce feedback light from the optical coupler to the laser light source.

8. 8. The laser interferometer according to claim 1, further comprising a third collimator provided between the laser light source and the optical coupler, for collimating the first laser light.

9. 9. The laser interferometer according to claim 1, further comprising an optical path length changing unit provided between the first collimator and the optical modulator, which changes the optical path length of an optical path along which the first laser light emitted from the first collimator propagates.

10. The optical path length changing unit a movable optical element that changes the optical path length by moving; a driving unit that drives the movable optical element; 10. The laser interferometer of claim 9, wherein:

11. The optical path length changing unit a refractive index variable body whose refractive index changes in response to an input of a control signal; an input unit for inputting the control signal to the refractive index variable body; 10. The laser interferometer of claim 9, wherein:

12. a demodulation circuit that demodulates the sample signal from the received light signal based on a reference signal; an oscillation circuit that operates using the vibration element as a signal source and outputs the reference signal; 12. The laser interferometer according to claim 1, wherein

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