Laser interferometer

Abstract

To provide a laser interferometer that can suppress entrance of return light to a laser light source and can suppress reduction of the accuracy of demodulating a sample signal derived from a measurement target object from a light reception signal.SOLUTION: The laser interferometer includes: a laser light source for emitting a laser beam; a shielding element with an opening through which the laser beam passes through; an optical modulator for modulating the laser beam to reference light with different frequencies; and a light reception element for receiving object light generated in such a manner that the laser beam is reflected by a measurement target object and the reference light, and outputting a light reception signal. When the diameter of the opening is φpin [mm], the relation of 0.10≤φpin≤10.0 is satisfied.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 an object to be measured, and measures the vibration velocity based on the scattered laser beam that has been subjected to a Doppler shift.

[0003] Specifically, the laser vibrometer described in Patent Document 1 includes an acousto-optic modulator (AOM). The acousto-optic modulator shifts the frequency of a laser beam by changing the frequency of the supplied ultrasonic waves. In the laser vibrometer, the frequency-shifted laser beam is used as a reference beam. Then, the scattered laser beam originating from the object to be measured and the reference beam originating from the acousto-optic modulator are superimposed to extract a beat frequency. The vibration velocity of the object to be measured is calculated from the beat frequency thus extracted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-285898 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a laser light source, the intrusion of returning light can cause the laser oscillation to become unstable. When the laser oscillation becomes unstable in the laser vibrometer described in Patent Document 1, the quality of the laser light decreases. This causes the S / N ratio (signal-to-noise ratio) to decrease and the phase of the oscillating laser light to become discontinuous in the laser vibrometer. As a result, there is a problem in that the measurement accuracy of the vibration velocity of an object decreases. [Means for solving the problem]

[0006] A laser interferometer according to an application example of the present invention includes: A laser light source that emits laser light; a shielding element having an opening through which the laser light passes; an optical modulator that modulates the laser light into a reference light having a different frequency; a light receiving element that receives object light generated by reflection of the laser light on a measurement object and the reference light and outputs a light receiving signal; Equipped with The diameter of the opening is φ pin [mm], 0.10≦φ pin ≦10.0. [Brief description of the drawings]

[0007] [Figure 1] 1 is a functional block diagram showing a laser interferometer according to a first embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing the configuration of a sensor head unit shown in FIG. [Diagram 3] 3 is a perspective view showing a first configuration example of the optical modulator shown in FIG. 2. [Figure 4] FIG. 11 is a plan view showing a part of a second configuration example of the optical modulator. [Diagram 5] FIG. 13 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 lights when incident light Ki is incident on the surface of a vibration element in a direction perpendicular to the surface. FIG. [Figure 7] 13 is a conceptual diagram illustrating an optical modulator configured so that the angle between the traveling direction of the incident light Ki and the traveling direction of the reference light L2 is 180°. FIG. [Figure 8] 13 is a conceptual diagram illustrating an optical modulator configured so that the angle between the traveling direction of the incident light Ki and the traveling direction of the reference light L2 is 180°. FIG. [Figure 9]13 is a conceptual diagram illustrating an optical modulator configured so that the angle between the traveling direction of the incident light Ki and the traveling direction of the reference light L2 is 180°. FIG. [Figure 10] 1 is a cross-sectional view showing an optical modulator having a package structure. [Figure 11] FIG. 1 is a circuit diagram showing a configuration of a single-stage inverter oscillator circuit. [Figure 12] 2 is an example of an LCR equivalent circuit of a vibration element. [Figure 13] 3 is a schematic diagram showing a light path of the emitted light L1 emitted from the laser light source shown in FIG. 2 and a light path of the reference light L2 generated by the emitted light L1 being reflected by an optical modulator and traveling toward the laser light source as return light L5. [Figure 14] FIG. 11 is a schematic configuration diagram showing a sensor head of a laser interferometer according to a second embodiment. [Figure 15] 15 is a schematic diagram showing the light path of the emitted light L1 emitted from the laser light source shown in FIG. 14 and the light path of the reference light L2 generated when the emitted light L1 is reflected by an optical modulator and travels toward the laser light source as return light L5. [Figure 16] FIG. 11 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a first modified example. [Figure 17] FIG. 11 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a second modified example. [Figure 18] FIG. 13 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a third modified example. [Figure 19] FIG. 13 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a fourth modified example. [Figure 20] FIG. 13 is a schematic structural diagram showing an optical system included in a laser interferometer according to a fifth modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] 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.

[0009] 1. First embodiment First, the laser interferometer according to the first embodiment will be described. FIG. 1 is a functional block diagram showing a laser interferometer according to the first embodiment. The laser interferometer 1 shown in FIG. 1 has a sensor head unit 51 equipped with an optical system 50 and an oscillation circuit 54, and a demodulation circuit 52 to which a light reception signal from the optical system 50 is input. 1.1.Sensor head FIG. 2 is a schematic diagram showing the configuration of the sensor head unit 51 shown in FIG.

[0010] 1.1.1.Optical system As described above, the sensor head unit 51 includes the optical system 50 . As shown in FIG. 2, the optical system 50 includes a laser light source 2, a collimating lens 3, a polarizing beam splitter 4 (light splitter), a quarter-wave plate 6, a quarter-wave plate 8, an analyzer 9, a light receiving element 10, a frequency shifter-type optical modulator 12, a set section 16 in which an object to be measured 14 is placed, and a shielding element 17.

[0011] The laser light source 2 emits an emission light L1 (laser light) of a predetermined wavelength. The light receiving element 10 converts the received light into an electrical signal. The optical modulator 12 includes a vibration element 30, and modulates the emission light L1 to generate a reference light L2 including a modulated signal. The set unit 16 may be provided as necessary, and is configured to allow the measurement object 14 to be placed thereon. The emission light L1 incident on the measurement object 14 is reflected as object light L3 including a sample signal, which is a Doppler signal derived from the measurement object 14.

[0012] The optical path of the output light L1 emitted from the laser light source 2 is referred to as optical path 18. Optical path 18 is coupled to optical path 20 by reflection from the polarizing beam splitter 4. On optical path 20, a quarter-wave plate 8 and an optical modulator 12 are arranged in this order from the polarizing beam splitter 4 side. Furthermore, optical path 18 is coupled to optical path 22 by transmission through the polarizing beam splitter 4. On optical path 22, a quarter-wave plate 6 and a setting unit 16 are arranged in this order from the polarizing beam splitter 4 side.

[0013] The optical path 20 is coupled to an optical path 24 by transmission through the polarizing beam splitter 4. On the optical path 24, an analyzer 9 and a light receiving element 10 are arranged in this order from the polarizing beam splitter 4 side.

[0014] The outgoing light L1 emitted from the laser light source 2 passes through the optical path 18 and the optical path 20 and enters the optical modulator 12. The outgoing light L1 also passes through the optical path 18 and the optical path 22 and enters the measurement object 14. The reference light L2 generated by the optical modulator 12 passes through the optical path 20 and the optical path 24 and enters the light receiving element 10. The object light L3 generated by reflection at the measurement object 14 passes through the optical path 22 and the optical path 24 and enters the light receiving element 10.

[0015] In this specification, the term "optical path" refers to a path along which light travels that is set between optical components, and the term "optical axis" described below refers to the central axis of a light beam passing through the optical path.

[0016] 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 a coherent emission light L1. A light source with a line width of MHz or less is preferably used for the laser light source 2. Specific examples include a gas laser such as a He-Ne laser, a semiconductor laser element such as a DFB-LD (Distributed feedback - laser diode), an FBG-LD (Laser diode with Fiber Bragg Grating), a VCSEL (Vertical Cavity Surface Emitting Laser), and an FP-LD (Fabry-Perot Laser Diode).

[0017] In particular, the laser light source 2 is preferably a semiconductor laser element. This allows the laser light source 2 to be particularly miniaturized. This allows the laser interferometer 1 to be miniaturized. In particular, the sensor head 51 of the laser interferometer 1, which houses the optical system 50, can be made smaller and lighter, which is also useful in terms of improving the operability of the laser interferometer 1.

[0018] 1.1.1.2. Collimating lenses The collimating lens 3 is a convex lens disposed between the laser light source 2 and the polarizing beam splitter 4. The collimating lens 3 collimates the outgoing light L1 emitted from the laser light source 2.

[0019] When the light L1 emitted from the laser light source 2 is sufficiently collimated, for example when a gas laser such as a He-Ne laser is used as the laser light source 2, the collimator lens 3 may be omitted.

[0020] Polarizing Beam Splitter The polarizing beam splitter 4 is a light splitter arranged between the laser light source 2 and the optical modulator 12, and between the laser light source 2 and the measurement object 14. The polarizing beam splitter 4 splits the output light L1 into reflected light L1a (first divided light) and transmitted light L1b (second divided light). The polarizing beam splitter 4 also has the function of transmitting P polarized light and reflecting S polarized light. Below, a case will be considered where output light L1, which is linearly polarized and has a ratio of P polarized light and S polarized light of, for example, 50:50, is incident on the polarizing beam splitter 4.

[0021] The reflected light L1a, which is S-polarized light reflected by the polarizing beam splitter 4, is converted into circularly polarized light by the quarter-wave plate 8 and enters the optical modulator 12. The circular polarization of the reflected light L1a that enters the optical modulator 12 is expressed as f m [Hz] and is reflected as reference light L2. Therefore, the reference light L2 has a frequency f mThe reference light L2 contains a modulation signal of 1 / 4 wavelength [Hz]. The reference light L2 is converted to P polarized light again when it passes through the quarter wave plate 8. The P polarized light of the reference light L2 passes through the polarizing beam splitter 4 and the analyzer 9 and enters the light receiving element 10.

[0022] The transmitted light L1b, which is P-polarized light transmitted through the polarizing beam splitter 4, is converted into circularly polarized light by the quarter-wave plate 6 and enters the moving object 14. The circular polarization of the transmitted light L1b that enters the object 14 is expressed as f d [Hz] and is reflected as object light L3. Therefore, object light L3 has a frequency of f d The object light L3 is converted to S-polarized light again when it passes through the quarter-wave plate 6. The S-polarized light of the object light L3 is reflected by the polarizing beam splitter 4, passes through the analyzer 9, and enters the light receiving element 10.

[0023] As described above, since the output light L1 has coherence, the reference light L2 and the object light L3 are incident on the light receiving element 10 as interference light.

[0024] Note that a non-polarizing beam splitter may be used instead of the polarizing beam splitter. In this case, the quarter-wave plate 6 and the quarter-wave plate 8 are not necessary, and the number of parts can be reduced, thereby making the laser interferometer 1 more compact. Also, a light splitter other than the polarizing beam splitter 4 may be used.

[0025] Analyzer Since the S-polarized light and the P-polarized light are mutually orthogonal and independent, simply superimposing them does not produce beats due to interference. Therefore, the light waves of the superimposed S-polarized light and P-polarized light are passed through an analyzer 9 that is tilted at 45 degrees to both the S-polarized light and the P-polarized light. By using the analyzer 9, it is possible to transmit light with common components and cause interference. As a result, the reference light L2 and the object light L3 interfere with each other in the analyzer 9, and |f m -f d Interference light with a frequency of |[Hz] is generated.

[0026] 1.1.1.5.Photodetector The reference light L2 and the object light L3 are incident on the light receiving element 10 via the polarizing beam splitter 4 and the analyzer 9. The reference light L2 and the object light L3 undergo optical heterodyne interference, and |f m -f d The interference light having a frequency of | [Hz] enters the light receiving element 10. By demodulating the sample signal from this interference light using a method described later, it is finally possible to obtain the movement of the measurement object 14, i.e., the vibration velocity and displacement. The light receiving element 10 can be, for example, a photodiode.

[0027] Optical Modulators FIG. 3 is a perspective view showing a first configuration example of the optical modulator 12 shown in FIG.

[0028] 1.1.1.6.1. Overview of the First Configuration Example of the Optical Modulator The frequency shifter type optical modulator 12 has an optical modulation oscillator 120. The optical modulation oscillator 120 shown in FIG.

[0029] The vibration element 30 is made of a material that repeats a mode of vibration in which the vibration is distorted in a direction along the surface when a potential is applied. In this configuration example, the vibration element 30 is a quartz crystal AT vibrator that vibrates in a thickness-shear manner along a vibration direction 36 in a high frequency region of the MHz band. A diffraction grating 34 is formed on the surface of the vibration element 30. The diffraction grating 34 has a structure in which grooves 32 having a component intersecting with the vibration direction 36, that is, a plurality of linear grooves 32 extending in a direction intersecting with the vibration direction 36, are periodically arranged.

[0030] The substrate 31 has a front surface 311 and a back surface 312 which are opposite to each other. The vibration elements 30 are arranged on the front surface 311. In addition, a pad 33 for applying a potential to the vibration elements 30 is provided on the front surface 311. Meanwhile, a pad 35 for applying a potential to the vibration elements 30 is also provided on the back surface 312.

[0031] The size of the substrate 31 is, for example, about 0.5 mm or more and 10.0 mm or less in terms of the long side. The thickness of the substrate 31 is, for example, about 0.10 mm or more and 2.0 mm or less. As an example, the shape of the substrate 31 is a square with each side measuring 1.6 mm, and the thickness is 0.35 mm.

[0032] The size of the vibration element 30 is, for example, about 0.2 mm to 3.0 mm in length, and the thickness of the vibration element 30 is, for example, about 0.003 mm to 0.5 mm.

[0033] As an example, the shape of the vibration element 30 is a square with each side being 1.0 mm long and the thickness being 0.07 mm. In this case, the vibration element 30 oscillates at a fundamental oscillation frequency of 24 MHz. Note that by changing the thickness of the vibration element 30 and taking into account overtones, the oscillation frequency can be adjusted in the range of 1 MHz to 1 GHz.

[0034] In FIG. 3, the diffraction grating 34 is formed on the entire surface of the vibration element 30, but it may be formed only on a part of it.

[0035] The magnitude of the optical modulation by the optical modulator 12 is given by the inner 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 of the vibration direction 36 of the vibration element 30. In this configuration example, the vibration element 30 vibrates in a thickness-shear manner, but since 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 it possible to perform optical modulation according to a principle described below.

[0036] The diffraction grating 34 shown in Fig. 3 is a blazed diffraction grating. A blazed diffraction grating is a diffraction grating whose cross-sectional shape is stepped. The linear grooves 32 of the diffraction grating 34 are provided so that their extension direction is perpendicular to the vibration direction 36.

[0037] When the drive signal Sd is supplied (AC voltage is applied) from the oscillation circuit 54 shown in Fig. 1 and Fig. 2 to the vibration element 30 shown in Fig. 3, the vibration element 30 oscillates. The power (drive power) required for the 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.

[0038] In addition, conventional optical modulators may require a structure to maintain the temperature of the optical modulator, making it difficult to reduce the volume. In addition, 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.

[0039] 1.1.1.6.2. Method of forming a diffraction grating The method of forming the diffraction grating 34 is not particularly limited, but an example is a method of forming a mold using a method using a mechanical ruling engine, and forming the grooves 32 on an electrode formed on the surface of the vibration element 30 of the quartz AT resonator by a nanoimprint method. Here, the reason for forming the grooves on the electrode is that in the case of a quartz AT resonator, in principle, high-quality thickness-shear vibration can be generated on the electrode. Note that the grooves 32 are not limited to being formed on the electrode, and may be formed on the surface of the material of the non-electrode portion. Also, instead of the nanoimprint method, a processing method using exposure and etching, an electron beam drawing lithography method, a focused ion beam processing method (FIB), or the like may be used.

[0040] 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 mirror film made of a dielectric multilayer film may be provided on the diffraction grating. By providing a metal film or a mirror film, the reflectance of the diffraction grating 34 can be increased.

[0041] Furthermore, a resist film may be formed on a chip or wafer of a quartz crystal AT resonator, processed by etching, and then the resist film may be removed, and then a metal film or a mirror film may be formed on the processed surface. In this case, the resist material is removed, so that there is no influence due to moisture absorption of the resist material, and the chemical stability of the diffraction grating 34 can be improved. In addition, by providing a highly conductive metal film such as Au or Al, it can be used as an electrode for driving the vibration element 30.

[0042] Alternatively, the diffraction grating 34 may be formed using techniques such as anodized alumina (porous alumina).

[0043] 1.1.1.6.3.Other configuration examples of optical modulators The vibration element 30 is not limited to a quartz crystal vibrator, and may be, for example, a Si vibrator, a surface acoustic wave (SAW) device, a ceramic vibrator, or the like.

[0044] 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.

[0045] 4 is a Si vibrator manufactured from a Si substrate using MEMS technology. MEMS (Micro Electro Mechanical Systems) is an abbreviation for micro-electromechanical systems.

[0046] 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 using electrostatic attraction as a driving force in the left-right direction of FIG. 4, that is, 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 the diffraction grating 34 to vibrate in-plane. The oscillation frequency of the Si vibrator is, for example, about 1 kHz to several hundreds of MHz.

[0047] The vibration element 30B shown in Fig. 5 is a SAW device that uses surface waves. SAW (Surface Acoustic Wave) is an abbreviation for surface acoustic wave.

[0048] 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 the diffraction grating 34 to vibrate in-plane. The oscillation frequency of the SAW device is, for example, about several hundred MHz to several GHz.

[0049] In the above-mentioned device, by providing the diffraction grating 34, optical modulation becomes possible according to the principle described below, as in the case of the quartz crystal AT resonator.

[0050] On the other hand, when the vibration element 30 is a quartz crystal oscillator, a highly accurate modulated signal can be generated by utilizing the extremely high Q value of the quartz crystal. The Q value is an index showing the sharpness of the resonance peak. In addition, a quartz crystal oscillator has the characteristic of being less susceptible to disturbances. Therefore, by using a modulated signal modulated by the optical modulator 12 having a quartz crystal oscillator, a sample signal derived from the measurement object 14 can be obtained with high accuracy.

[0051] 1.1.1.6.4.Light modulation by vibration elements Next, the principle of modulating light using the vibration element 30 will be described.

[0052] FIG. 6 shows the incident light K i 1 is a conceptual diagram illustrating how multiple diffracted beams are generated when light is incident on a substrate.

[0053] A light K is incident on a diffraction grating 34 that is vibrating in thickness-shear vibration along a vibration direction 36. i When the light is incident on the surface of the glass, the diffraction phenomenon occurs, resulting in multiple diffracted light beams K ns is generated. n is the diffracted light Kns where n is the order of the diffraction grating, and n=0, ±1, ±2, .... Note that the diffraction grating 34 shown in FIG. 6 is not the blazed diffraction grating shown in FIG. 3, but is a diffraction grating made of repeated concaves and convexes as an example of another diffraction grating. Also, in FIG. 6, diffracted light K 0s is omitted in the illustration.

[0054] 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 the incident angle is not particularly limited, and the incident angle may be set so that the light is incident obliquely on the surface of the vibration element 30. When the light is incident obliquely, the diffracted light K ns The direction of travel also changes accordingly.

[0055] Depending on the design of the diffraction grating 34, higher-order light of |n|≧2 may not appear. Therefore, in order to obtain a stable modulated signal, it is preferable to set |n|=1. That is, in the laser interferometer 1 of FIG. 2, it is preferable that the frequency shifter-type optical modulator 12 is arranged so that the ±1st-order diffracted light is used as the reference light L2. This arrangement can realize stable measurement by the laser interferometer 1.

[0056] 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 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 high frequency and miniaturization of the laser interferometer 1.

[0057] In this embodiment, as an example, the incident light K i The optical modulator 12 is configured so that the angle between the incoming direction of the reference beam L2 and the traveling direction of the reference beam L2 emitted from the optical modulator 12 is 180°. Three examples will be described below.

[0058] 7 to 9 show the incident light K i1 is a conceptual diagram illustrating an optical modulator 12 configured so that the angle between the traveling direction of the first light beam L1 and the traveling direction of the reference light L2 is 180°.

[0059] The optical modulator 12 shown in FIG. 7 includes a mirror 37 in addition to the vibration element 30. The mirror 37 reflects the diffracted light K 1s The mirror 37 is arranged to reflect the diffracted light K 1s The angle between the incident angle of the diffracted light K and the reflection angle of the mirror 37 is 180°. 1s is diffracted again by the diffraction grating 34 and enters the optical modulator 12. i Therefore, by adding the mirror 37, the incident light K i This satisfies the condition that the angle between the incident direction of the reference beam L1 and the traveling direction of the reference beam L2 is 180°.

[0060] Furthermore, by passing the reference light L2 through the mirror 37 in this manner, 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.

[0061] In Fig. 8, the vibration element 30 is tilted with respect to the arrangement in Fig. 6. The tilt angle θ S is the incident light K i The angle between the incident direction of the reference light L1 and the traveling direction of the reference light L2 is set to be 180°.

[0062] The diffraction grating 34 shown in FIG. B The blazed diffraction grating has the following structure: Incident light K i When the light is incident on the diffraction grating 34, it has a blaze angle θ B Therefore, the reference light L2 returns at the same angle as the incident angle β. BBy making it equal to the incident light K i The condition that the angle between the direction of incidence of the reference beam L2 and the direction of travel of the reference beam L2 is 180° can be satisfied. In this case, the above condition can be satisfied without using the mirror 37 shown in Fig. 7 and without tilting the vibration element 30 itself as shown in Fig. 8, so that the laser interferometer 1 can be made even smaller 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", and has the advantage of being able to particularly increase the diffraction efficiency of the diffracted light.

[0063] In addition, the pitch P in FIG. 9 represents the pitch of the blazed diffraction grating, and as an example, the pitch P is set to 1 μm. Also, the blazed angle θ B is set to, for example, 25°. In this case, in order to satisfy the above condition, the incident light K i The incident angle β with respect to the normal N should also be set to 25°.

[0064] PACKAGE STRUCTURE FIG. 10 is a cross-sectional view showing an optical modulator 12 having a package structure.

[0065] 10 includes a container 70 which is a housing, an optical modulation oscillator 120 housed in the container 70, and a circuit element 45 which constitutes an oscillation circuit 54. The container 70 is hermetically sealed in, for example, a reduced pressure atmosphere such as a vacuum, or an inert gas atmosphere such as nitrogen or argon.

[0066] 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.

[0067] 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.

[0068] 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). In addition, an 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.

[0069] 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 later.

[0070] By adopting such a package structure, the optical modulation oscillator 120 and the circuit element 45 can be stacked, so that the physical distance between them can be reduced, and the wiring length between the optical modulation oscillator 120 and the circuit element 45 can be shortened. This makes it possible to prevent external noise from entering the drive signal Sd, and conversely, to prevent the drive signal Sd from becoming a noise source. In addition, one container 70 can protect both the optical modulation oscillator 120 and the circuit element 45 from the external environment. This makes it possible to miniaturize the sensor head unit 51 while improving the reliability of the laser interferometer 1.

[0071] 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 individual package structures. Although not shown, the container 70 may also accommodate other circuit elements that configure the oscillation circuit 54. The container 70 may be provided as necessary, and may be omitted.

[0072] Furthermore, the optical modulator 12 is not limited to one including the vibration element 30 as described above, and may be, for example, an acousto-optical modulator (AOM), an electro-optical modulator (EOM), etc. When an AOM or EOM is applied to the optical modulator 12, a light reflecting function may be added to the AOM or EOM.

[0073] Shielding elements The shielding element 17 is an iris (aperture) disposed between the collimator lens 3 and the polarizing beam splitter 4. The shielding element 17 has an opening 172 provided corresponding to the optical path 18. The shielding element 17 suppresses the return light L5 generated by the optical modulator 12, the measurement object 14, etc. from entering the laser light source 2. The shielding element 17 has a very simple structure since it only needs to have the function of shielding the return light L5. This contributes to simplifying the structure of the laser interferometer 1. The shielding element 17 may be a slit, a pinhole, etc., and its structure is not particularly limited. The action and effect of the shielding element 17 will be described in detail later.

[0074] 1.1.2.Oscillation 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.

[0075] There are no particular limitations on the oscillator circuit 54, and circuits of various configurations can be used as long as they are capable of oscillating the vibration element 30. Fig. 11 is a circuit diagram showing the configuration of a single-stage inverter oscillator circuit as an example of the circuit configuration.

[0076] 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.

[0077] The circuit element 45 is an inverter IC. The terminals X1 and X2 of the circuit element 45 are terminals connected to 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.

[0078] A first capacitor Cg is connected between the terminal X1 and the ground potential. A limiting resistor Rd and a second capacitor Cd are connected in series between the terminal X2 and the ground potential, in that order from the terminal X2 side. Furthermore, one end of a feedback resistor Rf is connected between the terminal X1 and the first capacitor Cg, and the other end of the feedback resistor Rf is connected between the terminal X2 and the limiting resistor Rd.

[0079] In addition, 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. As a result, the vibration element 30 serves as a signal source for the oscillation circuit 54.

[0080] FIG. 12 is an example of an LCR equivalent circuit of the vibration element 30. As shown in FIG. 12, the LCR equivalent circuit of the vibration element 30 is made up of a series capacitance C1, a series inductance L1, an equivalent series resistance R1, and a parallel capacitance C0.

[0081] In the oscillator 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).

[0082]

number

[0083] Then, the oscillation frequency f output from the terminal Y of the oscillation circuit 54 is osc is given by the following equation (b).

[0084]

number

[0085] 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 value can be fine-tuned.

[0086] In addition, the natural frequency f Q and the oscillation frequency f of the oscillator circuit 54. osc The difference Δf between and is given by the following equation (c):

[0087]

number

[0088] Here, C1< <C0、C1<<C L Therefore, Δf is approximately given by the following equation (d).

[0089]

number

[0090] Therefore, the oscillation frequency f osc is the natural frequency f of the vibration element 30 Q The value depends on.

[0091] Here, when the vibration element 30 is fixed to, for example, a container 70, and is subjected to expansion stress due to temperature via the fixing part, the natural frequency f Q In addition, when the vibration element 30 is tilted, the natural frequency f Q fluctuates.

[0092] For this reason, the oscillator circuit 54 has a natural frequency fQ Even if fluctuates, the oscillation frequency f osc In other words, the oscillation frequency f osc is always Δf, and the natural frequency f Q This stabilizes the vibration of the vibration element 30 and the displacement amplitude. The stable displacement amplitude stabilizes the modulation characteristics of the optical modulator 12, so that the demodulation accuracy of the sample signal in the demodulation circuit 52 can be improved.

[0093] As an example, Δf = |f osc -f Q It is preferable that |≦3000 [Hz], and more preferably 600 [Hz].

[0094] As described above, in the laser interferometer 1 according to this embodiment, the optical modulator 12 includes the vibration element 30. The optical modulator 12 uses the vibration element 30 to modulate the reflected light L1a (laser light).

[0095] With this configuration, it is possible to reduce the size and weight of the optical modulator 12. As a result, it is possible to reduce the size and weight of the laser interferometer 1.

[0096] The laser interferometer 1 according to this embodiment also includes a demodulation circuit 52 and an oscillation circuit 54. The oscillation circuit 54 includes a vibration element 30 as its signal source, and outputs a reference signal Ss to the demodulation circuit 52, as shown in Fig. 1. The demodulation circuit 52 demodulates the sample signal derived from the measurement object 14 from the received light signal, based on the reference signal Ss.

[0097] According to this configuration, the natural frequency f Q Even if the oscillation frequency f of the oscillator circuit 54 fluctuates, osc The natural frequency f of the vibration element 30 QSince the temperature characteristic of the modulation signal can be changed to a value according to the temperature, the vibration of the vibration element 30 can be easily stabilized. This allows the temperature characteristic of the modulation signal to correspond to the temperature characteristic of the vibration element 30, and the modulation characteristic of the optical modulator 12 can be stabilized. As a result, the demodulation accuracy of the sample signal in the demodulation circuit 52 can be improved.

[0098] In addition, 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 fluctuation of the modulated signal accompanying temperature change coincides with or approximates the behavior of the fluctuation of the reference signal Ss. Therefore, even if the temperature of the vibration element 30 changes, the effect on the demodulation accuracy can be suppressed, and the demodulation accuracy of the sample signal derived from the measurement object 14 can be improved.

[0099] Furthermore, in this embodiment, since the power consumption of the oscillator circuit 54 is low, the power consumption of the laser interferometer 1 can be easily reduced.

[0100] Instead of the oscillator circuit 54, a signal generator such as a function generator or a signal generator may be used.

[0101] 1.2. Demodulation circuit The demodulation circuit 52 performs a demodulation process to demodulate a sample signal originating from the measurement object 14 from the light receiving signal output from the light receiving element 10. 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 speed of the measurement object 14 can be obtained from the frequency information. If different information can be obtained in this way, the laser interferometer 1 can be given the function of a displacement meter and a speed meter, thereby improving the functionality of the laser interferometer 1.

[0102] The circuit configuration of the demodulation circuit 52 is set according to the modulation processing method. In the laser interferometer 1 according to this embodiment, an optical modulator 12 including a vibration element 30 is used. Since the vibration element 30 is an element that vibrates simply, the vibration speed changes from moment to moment within the period. Therefore, the modulation frequency also changes with time, and a conventional demodulation circuit cannot be used as it is.

[0103] A conventional demodulation circuit refers to a circuit that demodulates a sample signal from a received light signal that includes a modulated signal modulated by, for example, an acousto-optic modulator (AOM). In an acousto-optic modulator, the modulation frequency does not change. Therefore, a conventional demodulation circuit can demodulate a sample signal from a received light signal that includes a modulated signal whose modulation frequency does not change, but cannot demodulate the sample signal as it is if the signal includes a modulated signal modulated by an optical modulator 12 whose modulation frequency changes.

[0104] 1 includes a pre-processing unit 53 and a demodulation processing unit 55. The light receiving signal output from the light receiving element 10 is first passed through the pre-processing unit 53 and then guided to the demodulation processing unit 55. The pre-processing unit 53 performs pre-processing on the light receiving signal. This pre-processing provides a signal that can be demodulated by a conventional demodulation circuit. Therefore, the demodulation processing unit 55 demodulates the sample signal derived from the measurement object 14 by a known demodulation method.

[0105] 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.

[0106] A current-voltage converter 531 and an ADC 532 are connected in this order from the light receiving element 10 side between the light receiving element 10 and the pre-processing unit 53. The current-voltage converter 531 is a transimpedance amplifier, and converts the current output from the light receiving element 10 into a voltage signal. The ADC 532 is an analog-digital converter, and converts an analog signal into a digital signal with a predetermined sampling bit number.

[0107] The current output from the light receiving element 10 is converted into a voltage signal by a current-voltage converter 531. The voltage signal is converted into a digital signal by an ADC 532 and split into two signals, a first signal S1 and a second signal S2, at a branching 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.

[0108] 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, and converts an analog signal into a digital signal with a predetermined number of sampling bits.

[0109] First band pass filter 534, second band pass filter 535 and third band pass filter 539 are each a filter that selectively transmits signals in a specific frequency band.

[0110] The first delay adjuster 536 and the second delay adjuster 537 are circuits that adjust the delay of a signal. The multiplier 538 is a circuit that generates an output signal proportional to the product of two input signals. The adder 542 is a circuit that generates an output signal proportional to the sum of two input signals.

[0111] 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.

[0112] The first signal S1 is passed through a first bandpass 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 by a second bandpass filter 535 described later. This delay adjustment makes it possible to equalize the delay time associated with passing through the filter circuits between the first bandpass filter 534 through which the first signal S1 passes and the second bandpass filter 535 and the third bandpass filter 539 through which the second signal S2 passes. The first signal S1 that has passed through the first delay adjuster 536 is input to a summer 542 via a first AGC 540.

[0113] 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, cos(ω m The reference signal Ss represented by ωt is converted into a digital signal by the ADC 533, the phase is adjusted by the second delay adjuster 537, and the signal is 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 is passed through a third bandpass filter 539, and then through a second AGC 541 and input to a summer 542.

[0114] The adder 542 outputs an output signal proportional to the sum of the first signal S 1 and the second signal S 2 to the demodulation processing unit 55 .

[0115] 1.2.2. Basic principles of pretreatment Next, the basic principle of preprocessing in the preprocessing unit 53 will be described. The basic principle here refers to the principle described in Japanese Patent Application Laid-Open No. 2-38889. In the following description, as an example, a system will be considered in which the frequency of the modulation signal changes sinusoidally and the displacement of the measurement object 14 also changes in simple harmonic motion in the optical axis direction. Here, E m , E d , φ,

[0116]

number

[0117] Then, the light receiving signal I output from the light receiving element 10 is PD is theoretically expressed by the following equation.

[0118]

number

[0119] In addition, E m , E d , φ m , φ d , φ, ω m , ω d , ω0, a m , a d are as follows, respectively.

[0120]

number

[0121] In addition, <> in equation (4) represents the time average. The first and second terms of the above formula (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:

[0122]

number

[0123] Here, the v-th order Bessel functions such as the following equations (8) and (9) are known.

[0124]

number

[0125] When the above formula (5) is expanded in a series using the Bessel functions of the above formulas (8) and (9), it can be transformed into the following formula (10).

[0126]

number

[0127] where J0(B), J1(B), J2(B), ... are Bessel coefficients.

[0128] By modifying it as described above, it can be said that, theoretically, it is possible to extract a band corresponding to a specific order by using a bandpass filter. Based on this theory, the pre-processing unit 53 performs pre-processing on the received light signal in the following flow.

[0129] First, the light receiving signal output from the ADC 532 is split into a first signal S1 and a second signal S2 by the splitter 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.

[0130]

number

[0131] On the other hand, the second signal S2 is passed through a second band pass filter 535. The central angular frequency of the second band pass filter 535 is set to a value different from the central angular frequency of the first band pass filter 534. Here, as an example, the central 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.

[0132]

number

[0133] 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.

[0134]

number

[0135] 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.

[0136]

number

[0137] 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.

[0138] The amplitude of the second signal S2 expressed by the above formula (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.

[0139] Then, the first signal S1 and the second signal S2 are added up by the adder 542. The result of the addition is expressed by the following formula (15).

[0140]

number

[0141] As shown in the above formula (15), as a result of the addition, unnecessary terms are eliminated and necessary terms can be extracted. This result is input to the demodulation processing unit 55.

[0142] 1.2.3. Demodulation Processing Section Configuration The demodulation processing unit 55 performs a demodulation process to demodulate the signal output from the pre-processing unit 53 into a sample signal originating from the measurement target 14. The demodulation process is not particularly limited, but may be a well-known quadrature detection method. The quadrature detection method is a method of performing a demodulation process by externally mixing mutually orthogonal signals with respect to the input signal.

[0143] 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.

[0144] 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 represented by −sin(ωt). m t) is multiplied by the reference signal Ss. 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.

[0145] 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 performs division by dividing signal y by signal x, and passes the output y / x through arctangent calculator 558 to obtain output atan(y / x).

[0146] Then, the output atan(y / x) is passed through the output circuit 559 to obtain the phase φ d is obtained. In the output circuit 559, phase unwrapping is performed by phase unwrapping when there is a phase jump of 2π between adjacent points. The displacement of the measurement object 14 can be calculated from the phase information output from the demodulation processing unit 55. This realizes a displacement meter. Also, the velocity can be obtained from the displacement. This realizes a speed meter.

[0147] Although the circuit configuration of the demodulation processing unit 55 has been described above, the circuit configuration of the above digital circuit is merely an example and is not limited to this. For example, the configuration of the pre-processing unit 53 is not limited to the above configuration. In addition, 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.

[0148] The circuit configuration of the demodulation processing unit 55 described above may be configured to obtain frequency information derived from the object to be measured 14. The velocity of the object to be measured 14 can be calculated based on the frequency information.

[0149] 1.3. Suppression of return light by shielding elements Next, the suppression of return light by the shielding element 17 will be described.

[0150] The light L1 emitted from the laser light source 2 is diffused due to the diffraction phenomenon of light. LD The diameter R of the emitted light L1 from the laser light source 2 is the distance x LD At a position distant from the target by 100 mm, the angle is expressed by the following equation (16) using the diffuse radiation angle θ.

[0151]

number

[0152] In the above formula (16), the second term is a term for diffraction. The diffraction phenomenon is generally expressed by the following formula (16-1).

[0153]

number

[0154] Second-order and higher-order diffraction terms are not taken into consideration because they are sufficiently small. In this case, m = 1 can be set. Also, since the diffuse radiation angle θ is generally small, θ<<1. Therefore, the above equation (16-1) can be transformed into the following equation (16-2).

[0155]

number

[0156] Then, the above equation (16) can be transformed into the following equation (16-3).

[0157]

number

[0158] From the above formula (16-3), the beam diameter R of the emitted light L1 emitted from the laser light source 2 when it enters the collimator lens 3 can be found.

[0159] Fig. 13 is a schematic diagram showing a light path of the output light L1 emitted from the laser light source 2 shown in Fig. 2, and a light path of the reference light L2 generated by reflecting the output light L1 at the optical modulator 12 and traveling as the return light L5 toward the laser light source 2. Note that in Fig. 13, for convenience of illustration, the optical path that is refracted on the way is shown as being elongated. Furthermore, the return light L5 may contain light originating from the object light L3 (not shown) in addition to the light originating from the reference light L2 shown in Fig. 13. Furthermore, the return light L5 may be composed of only the light originating from the object light L3.

[0160] 13, the center of the collimating lens 3 is set as the origin O (reference position), and the distance between the origin O and the optical modulator 12 is set as L. If the collimating lens 3 is omitted, the position where the collimated light is generated is set as the origin O (reference position). For example, in a gas laser such as a He-Ne laser, collimated light is emitted from the emission point, so the emission point is the origin. Also, the light diameter of the return light L5 when it reaches the collimating lens 3 is set as R'.

[0161] Then, the beam diameter R' of the return light L5 is expressed by the following formula (16-4).

[0162]

number

[0163] 13, the light intensity of the return light L5 reaching the laser light source 2 is suppressed by providing the blocking element 17. The principle behind this is described below.

[0164] The shielding element 17 is provided between the collimating lens 3 and the polarizing beam splitter 4. Therefore, the diameter φ of the opening 172 of the shielding element 17 pin is made smaller than the beam diameter R' of the return light L5, the light intensity of the return light L5 can be reduced. The return light L5 causes instability in the laser oscillation in the laser light source 2. Therefore, if the light intensity of the return light L5 can be reduced, the laser oscillation can be stabilized. Note that, if the opening 172 is not a perfect circle, the diameter φ pin is the diameter of a perfect circle inscribed in the opening 172.

[0165] Self-mixing coupling in the laser light source 2 is involved in the destabilization of laser oscillation due to the return light L5. Self-mixing coupling is quantified by an index M, which is the product of the "coupling coefficient" and the "amount of return light L5." Of these, the coupling coefficient is proportional to the inverse of the cavity length of the laser light source 2. For this reason, self-mixing coupling is likely to become apparent when the amount of return light L5 increases in a semiconductor laser element with a short cavity length. If self-mixing coupling can be suppressed in semiconductor laser elements, it is believed that self-mixing coupling can be suppressed in most types of light sources.

[0166] Here, the present inventors have determined that in order to suppress self-mixing coupling in the laser light source 2, the index M is M<10 -6 It was found that it is necessary to satisfy the following condition. This corresponds to satisfying OD6 when the light intensity shielding ability of the shielding element 17 is expressed as an optical density (OD value). Therefore, if the shielding element 17 has a shielding ability that satisfies OD6, it is possible to stabilize the laser oscillation.

[0167] In light of this, the light intensity P0 of the emitted light L1 and the light intensity P r It is sufficient that the relationship of the following formula (17) is satisfied.

[0168]

number

[0169] Here, the light intensity P'r is the light intensity of the return light L5 immediately before it enters the shielding element 17. The light intensity P'r of the return light L5 is expressed by the following formula (18). Note that the following formula (18) is an example in which the light intensity distribution of the output light L1 is a Gaussian distribution or a distribution similar thereto.

[0170]

number

[0171] In the above formula (18-1), P is the peak light intensity of the emitted light L1, r is the radial position from the central axis of the emitted light L1, and w is the distance from the center axis of the emitted light L1 to the peak light intensity (1 / e 2 is the distance from the central axis of the emitted light L1 in the radial direction to the position where θ=λ / r. Note that in the case of the emitted light L1, θ<<1, so θ=λ / r can be used. Therefore, w is expressed as in the above formula (18-1-1). Then, the above formula (18-1) can be transformed into the above formula (18-1-2). Note that in the above formula (18-2), Refl M is the optical reflectance of the optical modulator 12, and Refl S is the light reflectance of the measurement object 14. In the above formula (18-3), Δψ is the error in the installation angle of the pseudo half-wave plate composed of the two quarter-wave plates 6 and 8.

[0172] P1 expressed in the above formula (18-1) represents the light intensity of the output light L1 passing through the opening 172 of the shading element 17. P2 expressed in the above formula (18-2) represents the reflectance of the optical modulator 12 and the reflectance of the measurement object 14. P3 expressed in the above formula (18-3) represents the intensity of the light returning to the laser light source 2 side via the polarizing beam splitter 4 when unintended polarization occurs due to the allowable angle error of the 1 / 2 wave plate.

[0173] Considering the above formula (18), when the emitted light L1 and the returned light L5 are coaxial with each other, the light intensity Pr of the returned light L5 that is not blocked by the shielding element 17 and passes through the opening 172 is expressed by the following formula (19).

[0174]

number

[0175] In the above formula (19), x and y are positions along two mutually perpendicular axes in the cross section of the return light L5. If the light intensity distribution of the output light L1 is a Gaussian distribution, then w=2σ, where σ is the standard deviation of the light intensity distribution.

[0176] Therefore, the diameter φ of the opening 172 of the shielding element 17 is set so that the light intensity Pr calculated by the above formula (19) satisfies the above formula (17). pin This makes it possible to realize the laser interferometer 1 with stabilized laser oscillation.

[0177] Specifically, in this embodiment, the diameter φ of the opening 172 pin [mm] should satisfy the relationship of the following formula (20).

[0178]

number

[0179] Diameter φ of opening 172 pin When is within this range, the return light L5 can be blocked by the blocking element 17. This makes it possible to suppress the light intensity of the return light L5 reaching the laser light source 2 and to prevent the laser oscillation from becoming unstable.

[0180] 1.3.1. First calculation example As an example of the case where the light intensity Pr calculated by the above formula (19) satisfies the above formula (17), a first calculation example will be shown. The parameters and calculation results of the first calculation example are as shown in Table 1.

[0181] [Table 1]

[0182] In the first calculation example, as shown in Table 1, the diameter φ of the opening 172 of the shielding element 17 pin 0.1 mm, and the distance between the collimating lens 3 and the laser light source 2 x LD By setting the angle of the half-wave plate to 4.0 mm and limiting the error Δψ to 1.0 deg, P r The calculation result of / P0 is 1×10 -6 Therefore, in the first calculation example, the incidence of the return light L5 on the laser light source 2 can be suppressed to a degree that does not cause the laser oscillation to become unstable.

[0183] The error Δψ in the installation angle of the half-wave plate is allowed as an assembly error if it is preferably 0.5 degrees or less, and more preferably 0.2 degrees or less. Therefore, if the error Δψ is within the above range, a laser interferometer 1 with excellent manufacturability can be realized.

[0184] 1.3.2. 2nd to 6th calculation examples As an example of the case where the light intensity Pr calculated by the above formula (19) satisfies the above formula (17), calculation examples 2 to 6 are shown. The parameters and calculation results of the first to sixth calculation examples are as shown in Table 2.

[0185] [Table 2]

[0186] In the second calculation example, as shown in Table 2, the diameter φ of the opening 172 of the shielding element 17 pin 0.4 mm, and the distance between the collimating lens 3 and the laser light source 2 x LD By setting the angle of the half-wave plate to 4.0 mm and limiting the error Δψ to 0.2 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0187] In the third calculation example, as shown in Table 2, the diameter φ of the opening 172 of the shielding element 17 is pin 2.0 mm, and the distance x between the collimating lens 3 and the laser light source 2 LD By setting the angle of the half-wave plate to 0.2 deg, the P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0188] In the fourth calculation example, as shown in Table 2, the diameter φ of the opening 172 of the shielding element 17 is pin 2.0 mm, and the distance x between the collimating lens 3 and the laser light source 2 LD By setting the angle of the half-wave plate to 45.0 mm and limiting the error Δψ to 1.0 deg, Pr The calculation result of / P0 is 1×10 -6 It will be less than.

[0189] In the fifth calculation example, as shown in Table 2, the diameter φ of the opening 172 of the shielding element 17 is pin 6.0 mm, the distance between the collimating lens 3 and the laser light source 2 x LD By setting the angle of the half-wave plate to 0.2 deg, the P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0190] In the sixth calculation example, as shown in Table 2, the diameter φ of the opening 172 of the shielding element 17 is pin 10.0 mm, the distance between the collimating lens 3 and the laser light source 2 x LD By setting the angle of the half-wave plate to 0.2 deg, the P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0191] Therefore, in the second to sixth calculation examples, 0.10≦φ pin By satisfying the condition ≦10.0, the incidence of the return light L5 on the laser light source 2 can be suppressed to a level that does not cause the laser oscillation to become unstable.

[0192] 1.4. Advantages of the First Embodiment As described above, the laser interferometer 1 according to this embodiment includes the laser light source 2, the shielding element 17, the optical modulator 12, and the light receiving element 10. The laser light source 2 emits the emitted light L1 (laser light). The shielding element 17 has an aperture 172 through which the emitted light L1 passes. The optical modulator 12 modulates the emitted light L1 into a reference light L2 having a different frequency. The light receiving element 10 receives the object light L3 generated when the emitted light L1 is reflected by the measurement object 14, and the reference light L2, and outputs a light receiving signal. The diameter of the aperture 172 is defined as φ pin [mm], the laser interferometer 1 is 0.10≦φ pin <= 10.0.

[0193] According to this configuration, the diameter φ is set within the above range depending on other parameters. pin By appropriately selecting, it is possible to sufficiently suppress the light intensity of the return light L5 incident on the laser light source 2. This makes it possible to stabilize the laser oscillation in the laser light source 2. As a result, the quality of the emitted light L1 is stabilized, making it possible to suppress a decrease in the accuracy of demodulating the sample signal from the received light signal in the demodulation circuit 52.

[0194] In this embodiment, the emitted light L1 and the returned light L5 are coaxial with each other. Therefore, compared to a case where the emitted light L1 and the returned light L5 are non-coaxial with each other as described below, the adjustment work of the laser interferometer 1 is easier and the working distance of the laser interferometer 1, i.e., the distance to the measurement object 14 that can be measured by the laser interferometer 1, can be secured relatively long. Therefore, according to this embodiment, it is possible to realize a laser interferometer 1 that has good measurement accuracy of the displacement and speed of the measurement object 14 and is easy to operate.

[0195] The diameter of the opening 172 is φ pin , 0.10≦φ pin ≦6.00, and 0.30≦φ pin It is more preferable that φ satisfies 0.30≦φ≦3.00. pin It is more preferable that the ratio satisfies ≦1.00.

[0196] Diameter φ of opening 172 pin If the diameter φ of the aperture 172 is smaller than the lower limit, the light intensity of the emitted light L1 passing through the aperture 172 becomes extremely small. This reduces the S / N ratio of the received light signal, and the measurement accuracy of the displacement and speed of the measurement object 14 decreases. pin exceeds the upper limit, the light intensity that can be reduced by the shading element 17 becomes small. Therefore, the light intensity of the return light L5 entering the laser light source 2 cannot be reduced sufficiently.

[0197] Furthermore, the emitted light L1 (laser light) incident on the optical modulator 12 may be non-collimated light, but in this embodiment it is collimated light. This makes it possible to prevent the optical modulator 12 and the polarizing beam splitter 4 from becoming large, thereby enabling the laser interferometer 1 to be made smaller and lighter. In addition, it makes it possible to prevent the diameter of the emitted light L1 from increasing, making it easier to increase the S / N ratio of the received light signal.

[0198] The light intensity distribution in the cross section of the collimated light may be any distribution, but is preferably a Gaussian distribution. When the standard deviation of the Gaussian distribution is σ [mm], the diameter φ of the aperture 172 is pin [mm] is 0.5σ≦φ pin It is preferable that the relationship φ / 2≦3.0σ is satisfied. In this case, about 10 to 99% of the light intensity of the output light L1 emitted from the laser light source 2 passes through the opening 172. In addition, the diameter φ of the opening 172 is preferably φ / 2≦3.0σ. pin [mm] is 1.0σ≦φ pin It is more preferable that the relationship φ / 2≦3.0σ is satisfied. In this case, about 40 to 99% of the light intensity of the output light L1 emitted from the laser light source 2 passes through the opening 172. The diameter φ of the opening 172 is φ1. pin As a result of setting [mm] within such a range, it is possible to ensure a necessary and sufficient light intensity for the emitted light L1 passing through the opening 172. As a result, it is possible to suppress a decrease in the S / N ratio in the received light signal, and to suppress a decrease in the measurement accuracy of the displacement and speed of the measurement object 14.

[0199] In addition, the distance x between the collimating lens 3 and the laser light source 2 LD corresponds to the focal length of the collimating lens 3. Distance x LD is preferably 1.5 mm or more and 70.0 mm or less, and more preferably 2.5 mm or more and 45.0 mm or less. pin If x is 2 mm or more, LD It is preferable that the distance between the center of the disk and the center of the y-axis is 15.0 mm or more and 45.0 mm or less. This makes it possible to further expand the allowable range of the error Δψ.

[0200] The distance L between the collimator lens 3 and the optical modulator 12 is preferably 5.0 mm or more and 200 mm or less, and more preferably 10.0 mm or more and 100 mm or less. This makes it possible to ensure a sufficient working distance while preventing the optical system 50 from becoming large.

[0201] In addition, the distance L between the collimator lens 3 and the shielding element 17 pin is preferably 0.5 mm or more and 15.0 mm or less, and more preferably 1.0 mm or more and 10.0 mm or less. This allows the shielding element 17 to function effectively while preventing the optical system 50 from becoming large.

[0202] 2. Second embodiment Next, a laser interferometer according to a second embodiment will be described. Fig. 14 is a schematic diagram showing the configuration of a sensor head of a laser interferometer 1 according to a second embodiment. Fig. 15 is a schematic diagram showing a light trail of the output light L1 emitted from the laser light source 2 shown in Fig. 14, and a light trail of the reference light L2 generated by reflecting the output light L1 at the optical modulator 12 and traveling as return light L5 toward the laser light source 2.

[0203] The second embodiment will be described below, focusing on the differences from the first embodiment and omitting the description of the similarities. In each drawing, the same reference numerals are used to designate the same components as those in the first embodiment.

[0204] 2.1. Suppression of return light by using shielding elements and shifting the optical axis In the first embodiment described above, the emitted light L1 and the return light L5 have a coaxial relationship. In contrast, in the second embodiment, the emitted light L1 and the return light L5 have a non-coaxial relationship. Specifically, as shown in FIG. 14 and FIG. 15, the optical modulator 12 is tilted so that the optical axis of the reference light L2 generated by the optical modulator 12 is shifted from the optical axis of the reflected light L1a (emitted light L1) incident on the optical modulator 12. As a result, even if a part of the reference light L2 is reflected again by the polarizing beam splitter 4 to generate the return light L5, the optical axis (first optical axis A1) of the emitted light L1, which is a collimated light, and the optical axis (second optical axis A2) of the return light L5 derived from the reference light L2 have a non-coaxial relationship. As a result, it is possible to suppress the return light L5 from being incident on the laser light source 2. In this specification, shifting the first optical axis A1 and the second optical axis A2 is referred to as "optical axis shifting". The first optical axis A1 is the optical axis of the output light L1, and the second optical axis A2 is the optical axis of the reference light L2 and the optical axis of the return light L5 derived from the reference light L2. Note that the direction in which the optical axes are shifted may be within the plane in which the optical system 50 extends, or may be a direction intersecting this plane, as shown in FIG.

[0205] As a result of the optical axis shift, a shift occurs between the first optical axis A1 and the second optical axis A2 at the position of the collimator lens 3. In FIG. 15, the shift width between the first optical axis A1 and the second optical axis A2 at the collimator lens 3 is Δy [mm]. Also in FIG. 15, the angle between the first optical axis A1 and the second optical axis A2 is the shift angle θ'. Furthermore, the distance between the center of the collimator lens 3 and the optical modulator 12 is L. Then, the shift width Δy is expressed by the following formula (21).

[0206]

number

[0207] On the other hand, the deviation angle θ′ is usually θ′<<1. Therefore, the above formula (21) is transformed into the following formula (22).

[0208]

number

[0209] Considering the deviation width Δy thus obtained, the formula (19) in the first embodiment can be replaced by the following formula (23).

[0210]

number

[0211] In the above formula (23-1), R pin is the diameter of the return light L5 in the shielding element 17, and L pin is the distance between the center of the collimating lens 3 and the center of the shielding element 17. Therefore, the diameter φ of the opening 172 of the shielding element 17 is set so that the light intensity Pr calculated by the above formula (23) satisfies the above formula (17). pin and the shift width Δy may be selected accordingly, thereby realizing a laser interferometer 1 with stabilized laser oscillation.

[0212] Of these, the diameter φ of the opening 172 of the shielding element 17 pin This is the same as in the first embodiment. On the other hand, it is preferable that the deviation width Δy [mm] satisfies the relationship of the following formula (24).

[0213]

number

[0214] When the shift width Δy is within this range, most of the return light L5 can be blocked by the blocking element 17. This makes it possible to suppress the light intensity of the return light L5 reaching the laser light source 2 and to prevent the laser oscillation from becoming unstable.

[0215] 2.1.1. Seventh calculation example As an example of the case where the light intensity Pr calculated by the above formula (23) satisfies the above formula (17), a seventh calculation example will be shown. The parameters and calculation results of the seventh calculation example are as shown in Table 3.

[0216] [Table 3]

[0217] In the seventh calculation example, as shown in Table 3, the diameter φ of the opening 172 of the shielding element 17 is pin is 0.50 mm (≒0.7σ), the deviation width Δy of the return light L5 in the collimating lens 3 is 0.10 mm, and the distance x between the collimating lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 4.0 mm and limiting the error Δψ to 0.2 deg, P r The calculation result of / P0 is 1×10 -6 Therefore, in the seventh calculation example, the incidence of the return light L5 on the laser light source 2 can be suppressed to a degree that does not cause the laser oscillation to become unstable.

[0218] 2.1.2. Calculation examples 8th to 16th As an example of the case where the light intensity Pr calculated by the above formula (23) satisfies the above formula (17), calculation examples 8 to 16 are shown. The parameters and calculation results of calculation examples 7 to 16 are as shown in Table 4.

[0219] [Table 4]

[0220] In the eighth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 pin is 2.10 mm (≒ 3.0σ), the deviation width Δy of the return light L5 in the collimating lens 3 is 1.80 mm, and the distance x between the collimating lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 4.0 mm and limiting the error Δψ to 0.2 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0221] In the seventh and eighth calculation examples, the diameter φ of the opening 172 is pin , 0.5σ≦φ pin / 2≦3.0σ, and the deviation width Δy is 0.10 mm≦Δy≦10.0 mm, so that the ratio P r It is confirmed that / P0 satisfies the relationship of formula (17) above.

[0222] In the ninth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 pin is 0.70 mm (≒ 1.0σ), the deviation width Δy of the return light L5 in the collimator lens 3 is 0.75 mm, and the distance x between the collimator lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 4.0 mm and limiting the error Δψ to 1.0 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0223] In the tenth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 pin is 2.10 mm (≒ 3.0σ), the deviation width Δy of the return light L5 in the collimating lens 3 is 2.30 mm, and the distance x between the collimating lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 4.0 mm and limiting the error Δψ to 1.0 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0224] In the ninth and tenth calculation examples, the diameter φ of the opening 172 is pin , 1.0σ≦φ pin / 2≦3.0σ and the deviation width Δy is set to 0.70 mm≦Δy≦10.0 mm, so even if the error Δψ is allowed up to 1.0 deg, the ratio P r It is confirmed that / P0 satisfies the relationship of formula (17) above.

[0225] In the eleventh calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 pinis 1.60 mm (≒ 3.0σ), the deviation width Δy of the return light L5 in the collimator lens 3 is 1.40 mm, and the distance x between the collimator lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 0.2 deg, the P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0226] In the twelfth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 pin is 0.40 mm (≒0.7σ), the deviation width Δy of the return light L5 in the collimating lens 3 is 0.10 mm, and the distance x between the collimating lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 0.2 deg, the P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0227] In the eleventh and twelfth calculation examples, the diameter φ of the opening 172 is pin , 0.5σ≦φ pin / 2≦3.0σ, and the deviation width Δy is set to 0.70 mm≦Δy≦10.0 mm, so that the distance L and the distance L pin Even if the length is shortened, the ratio P r It is confirmed that / P0 satisfies the relationship of the above formula (17). This allows the volume of the sensor head portion 51 of the laser interferometer 1 to be reduced to, for example, about 10 cc or less. As a result, the laser interferometer 1 can be particularly miniaturized.

[0228] In the thirteenth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 is pin is 0.53 mm (≒ 1.0σ), the deviation width Δy of the return light L5 in the collimator lens 3 is 0.50 mm, and the distance x between the collimator lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 3.0 mm and limiting the error Δψ to 1.0 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0229] In the fourteenth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 is pin is 1.90 mm (≒ 3.0σ), the deviation width Δy of the return light L5 in the collimator lens 3 is 2.10 mm, and the distance x between the collimator lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 3.0 mm and limiting the error Δψ to 1.0 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0230] In the thirteenth and fourteenth calculation examples, the diameter φ of the opening 172 is pin 1.0σ≦φ pin By setting / 2≦3.0σ and setting the deviation Δy to 0.50 mm≦Δy≦10.0 mm, even if the volume of the sensor head portion 51 is reduced to, for example, about 10 cc or less, it becomes possible to tolerate an error Δψ of up to 1.0 deg.

[0231] In the fifteenth calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 is pin is 6.00 mm, the deviation width Δy of the return light L5 in the collimator lens 3 is 2.00 mm, and the distance x between the collimator lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 40 mm and limiting the error Δψ to 0.2 deg, P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0232] In the 16th calculation example, as shown in Table 4, the diameter φ of the opening 172 of the shielding element 17 is pin is 10.0 mm, the deviation width Δy of the return light L5 in the collimator lens 3 is 3.50 mm, and the distance x between the collimator lens 3 and the laser light source 2 is LD By setting the angle of the half-wave plate to 0.2 deg, the P r The calculation result of / P0 is 1×10 -6 It will be less than.

[0233] Therefore, in the seventh to sixteenth calculation examples, 0.10≦φ pin By satisfying the condition ≦10.0, the incidence of the return light L5 on the laser light source 2 is suppressed to a degree that does not cause the laser oscillation to become unstable.

[0234] 2.2. Advantages of the Second Embodiment As described above, in the laser interferometer 1 according to this embodiment, the optical axis of the emitted light L1, which is a collimated light, is defined as the "first optical axis A1", and when the reference light L2 or the object light L3 is generated to return light L5 toward the laser light source 2, the optical axis of the return light L5 is defined as the "second optical axis A2". In addition, the position where the collimated light is generated, that is, the center of the collimator lens 3, is defined as the reference position, and the deviation width between the first optical axis A1 and the second optical axis A2 at the reference position is defined as Δy [mm]. In the laser interferometer 1 according to this embodiment, the first optical axis A1 and the second optical axis A2 are deviated so as to satisfy 0.10≦Δy≦10.0.

[0235] According to this configuration, the first optical axis A1 of the emitted light L1 and the second optical axis A2 of the return light L5 are non-coaxial with each other. As a result, the second optical axis A2 of the return light L5 is shifted from the center of the opening 172 of the shielding element 17. As a result, the diameter φ of the opening 172 pin It is possible to prevent the return light L5 from entering the laser light source 2 without narrowing the aperture. Therefore, according to this embodiment, it is possible to stabilize the laser oscillation in the laser light source 2 while improving the S / N ratio in the received light signal. As a result, the quality of the emitted light L1 is stabilized, and the accuracy of demodulating the sample signal from the received light signal in the demodulation circuit 52 can be improved. This makes it possible to improve the measurement accuracy of the displacement and speed of the measurement object 14.

[0236] Furthermore, if the deviation Δy is within the above range, the error Δψ in the installation angle of the half-wave plate can be easily suppressed to within an allowable range for assembly error, thereby realizing a laser interferometer 1 that is easy to manufacture.

[0237] The deviation width Δy preferably satisfies 0.50≦Δy≦10.0, more preferably satisfies 2.10≦Δy≦10.0, and even more preferably satisfies 2.30≦Δy≦10.0. In addition, taking into consideration the size of the sensor head portion 51, the upper limit value of the deviation width Δy is more preferably 6.00 or less, and even more preferably 3.00 or less.

[0238] If the deviation width Δy falls below the lower limit, the light intensity of the return light L5 entering the laser light source 2 increases and the allowable range of the error Δψ narrows, which may reduce the ease of manufacturing the optical system 50. On the other hand, if the deviation width Δy exceeds the upper limit, the polarization beam splitter 4 needs to be increased in size, which may make it difficult to reduce the size of the sensor head unit 51.

[0239] Moreover, the laser interferometer 1 according to this embodiment includes a collimating lens 3. The collimating lens 3 is disposed between the laser light source 2 and the shading element 17. The collimating lens 3 collimates the emission light L1 (laser light) emitted from the laser light source 2 to generate collimated light.

[0240] According to this configuration, collimated light can be generated even when a semiconductor laser element is used as the laser light source 2. This makes it possible to prevent the polarization beam splitter 4 from becoming large, and to achieve a reduction in size and weight of the laser interferometer 1. In addition, it is possible to prevent the beam diameter of the emitted light L1 from expanding, making it easier to increase the S / N ratio of the received light signal.

[0241] 3. First to fifth modified examples of laser interferometer Next, the laser interferometers according to the first to fifth modifications will be described.

[0242] Fig. 16 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a first modified example. Fig. 17 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a second modified example. Fig. 18 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a third modified example. Fig. 19 is a schematic diagram showing a mounting structure of an optical system included in a laser interferometer according to a fourth modified example.

[0243] The first to fourth modified examples will be described below, but in the following description, the differences from the above embodiment will be mainly described, and the description of the similarities will be omitted. Note that in Fig. 16 to Fig. 19, the same reference numerals are used for the same configurations as the above embodiment.

[0244] The optical system 50D of the laser interferometer 1 shown in Fig. 16 includes a substrate 39. The laser light source 2, the optical modulator 12, and the light receiving element 10 are each mounted on this substrate 39. The light receiving element 10, the laser light source 2, and the optical modulator 12 are arranged in this order on the substrate 39 shown in Fig. 16 along a direction perpendicular to the optical path 22.

[0245] 16 also includes prisms 40 and 42. The prism 40 is provided on the optical path 24 between the light receiving element 10 and the analyzer 9. The prism 42 is provided on the optical path 20 between the optical modulator 12 and the quarter-wave plate 8.

[0246] 16 further includes a collimating lens 44. The collimating lens 44 is provided on the optical path 18 between the laser light source 2 and the polarizing beam splitter 4. In the first modified example as described above, the same effects as those of the above embodiment can be obtained.

[0247] An optical system 50E of a laser interferometer 1 shown in FIG. 17 is similar to the optical system 50D shown in FIG. 16, except that the arrangement of elements and the like is different.

[0248] 17, a laser light source 2, a light receiving element 10, and an optical modulator 12 are arranged in this order along a direction perpendicular to the optical path 22. A prism 40 is provided on the optical path 18, and a prism 42 is provided on the optical path 20. In the second modified example as described above, the same effects as those of the above embodiment can be obtained.

[0249] An optical system 50F of a laser interferometer 1 shown in FIG. 18 is similar to the optical system 50E shown in FIG. 17, except that the arrangement of elements and the like is different, and the laser light received by the light receiving element 10 is different.

[0250] 18, a laser light source 2, an optical modulator 12, and a light receiving element 10 are arranged in this order along a direction perpendicular to the optical path 22. A prism 42 is provided on the optical path 24.

[0251] The outgoing light L1 emitted from the laser light source 2 passes through the prism 40 and is split into two by the polarizing beam splitter 4. The outgoing light L1 reflected by the polarizing beam splitter 4 passes through the quarter-wave plate 6 and is incident on the moving measurement object 14. The outgoing light L1 undergoes a Doppler shift at the measurement object 14 and is reflected as object light L3. The object light L3 passes through the quarter-wave plate 6, the polarizing beam splitter 4, and the quarter-wave plate 8 and is incident on the optical modulator 12. The object light L3 undergoes a frequency shift at the optical modulator 12 and is reflected as object reference light L4. The object reference light L4 passes through the quarter-wave plate 8, the polarizing beam splitter 4, the prism 42, and the analyzer 9 and is incident on the light receiving element 10.

[0252] On the other hand, the outgoing light L 1 transmitted through the polarizing beam splitter 4 passes through a prism 42 and an analyzer 9 and enters the light receiving element 10 .

[0253] Then, the object reference light L4 and the outgoing light L1 are incident as interference light on the light receiving element 10. The object reference light L4 is a laser light including a modulation signal and a sample signal. In addition, in this modified example, the light receiving element 10 receives the interference light between the object reference light L4 and the emitted light L1, and the demodulation circuit 52 demodulates the sample signal contained in the object reference light L4 based on the reference signal Ss and the modulated signal contained in the object reference light L4. In the third modified example as described above, the same effects as those of the above embodiment can be obtained.

[0254] An optical system 50G of a laser interferometer 1 shown in FIG. 19 is similar to the optical system 50F shown in FIG. 18, except that the orientation of the light reflecting surface of the polarizing beam splitter 4 is different.

[0255] The light L1 emitted from the laser light source 2 passes through a prism 40 and is split into two by a polarizing beam splitter 4.

[0256] The outgoing light L1 reflected by the polarizing beam splitter 4 passes through the quarter-wave plate 8 and enters the optical modulator 12. The outgoing light L1 undergoes a frequency shift in the optical modulator 12 and is reflected as reference light L2. The reference light L2 passes through the quarter-wave plate 8, the polarizing beam splitter 4, and the quarter-wave plate 6 and enters the measuring object 14 in a moving state. The reference light L2 undergoes a Doppler shift in the measuring object 14 and is reflected as object reference light L4. The object reference light L4 passes through the quarter-wave plate 6, the polarizing beam splitter 4, the prism 42, and the analyzer 9 and enters the light receiving element 10.

[0257] On the other hand, the outgoing light L 1 transmitted through the polarizing beam splitter 4 passes through a prism 42 and an analyzer 9 and enters the light receiving element 10 .

[0258] Then, the object reference light L4 and the outgoing light L1 are incident as interference light on the light receiving element 10. The object reference light L4 is a laser light including a modulation signal and a sample signal. Also in this modified example, the light receiving element 10 receives the interference light between the object reference light L4 and the emitted light L1, and the demodulation circuit 52 demodulates the sample signal contained in the object reference light L4 based on the reference signal Ss and the modulated signal contained in the object reference light L4. In the fourth modified example as described above, the same effects as those of the above embodiment can be obtained.

[0259] 16 to 19, it is possible to easily reduce the size of the laser interferometer 1. The arrangement of the elements is not limited to the arrangement shown in the figures.

[0260] 16 to 19, the size of the light receiving element 10 is, for example, 0.1 mm square, the size of the laser light source 2 is, for example, 0.1 mm square, and the size of the optical modulator 12 is, for example, 0.5 to 10 mm square. The size of the board 39 on which these are mounted is, for example, 1 to 10 mm square. This makes it possible to miniaturize the optical system to approximately the size of the board 39.

[0261] Each of the above embodiments and modifications has a so-called Michelson type interference optical system. In contrast, the optical system 50H of the laser interferometer 1 shown in Fig. 20 is different in that it is a Mach-Zehnder type interference optical system. The present invention is also applicable to a laser interferometer having a Mach-Zehnder type interference optical system. Fig. 20 is a schematic structural diagram showing an optical system 50H included in a laser interferometer 1 according to a fifth modified example. Note that Fig. 20 shows only main optical elements, with some parts omitted.

[0262] 20 includes a laser light source 2, polarizing beam splitters 4a, 4b, and 4c (light splitters), a quarter-wave plate 6, a half-wave plate 7, an analyzer 9, an optical modulator 12H, a mirror 41, a light receiving element 10, and a shielding element 17. In the optical system 50H, the optical modulator 12H has optical transparency. For this reason, examples of the optical modulator 12H include an acousto-optic modulator (AOM) and an electro-optic modulator (EOM). In the fifth modified example as described above, the blocking element 17 is provided and the optical modulator 12H is tilted as necessary to prevent the return light L5 from entering the laser light source 2. Therefore, the fifth modified example can also provide the same effect as the above embodiment.

[0263] Although 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. Any other configuration may be added to the laser interferometer according to the embodiment. The laser interferometer of the present invention may also include any two or more of the embodiment and the modified examples.

[0264] The laser interferometer of the present invention can be applied not only to the displacement meter and speed meter described above, but also to, for example, a vibrometer, an inclinometer, a distance meter (length measuring device), etc. Applications of the laser interferometer of the present invention include optical comb interferometry technology that enables distance measurement, 3D imaging, spectroscopy, etc., and optical fiber gyros that realize angular velocity sensors, angular acceleration sensors, etc. [Explanation of symbols]

[0265] 1...laser interferometer, 2...laser light source, 3...collimating lens, 4...polarizing beam splitter, 4a...polarizing beam splitter, 4b...polarizing beam splitter, 4c...polarizing beam splitter, 6...1 / 4 wave plate, 7...1 / 2 wave plate, 8...1 / 4 wave plate, 9...analyzer, 10...light receiving element, 12...optical modulator, 12H...optical modulator, 14...measurement object, 16...set unit, 17...shielding element, 18...optical path, 20...optical path, 22...optical path, 24...optical path, 30...vibration element, 30A...vibration element, 3 0B...vibration element, 31...substrate, 32...groove, 33...pad, 34...diffraction grating, 35...pad, 36...vibration direction, 37...mirror, 39...substrate, 40...prism, 41...mirror, 42...prism, 44...collimating lens, 45...circuit element, 50...optical system, 50D...optical system, 50E...optical system, 50F...optical system, 50G...optical system, 50H...optical system, 51...sensor head unit, 52...demodulation circuit, 53...preprocessing unit, 54...oscillating circuit, 55...demodulation processing unit, 70...container, 72...container body, 74... Lid, 76...bonding wire, 120...optical modulation oscillator, 172...opening, 301...first electrode, 302...second electrode, 303...diffraction grating mounting portion, 305...piezoelectric substrate, 306...comb-shaped electrode, 307...ground electrode, 311...front surface, 312...rear surface, 531...current-voltage converter, 532...ADC, 533...ADC, 534...first bandpass filter, 535...second bandpass filter, 536...first delay adjuster, 537...second delay adjuster, 538...multiplier, 539...third bandpass filter filter, 540...first AGC, 541...second AGC, 542...summer, 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, A1...first optical axis, A2...second optical axis, C0...parallel 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...incident light, L1...series inductance, L1...emitted light, L1a...reflected light, L1b...transmitted light, L2...reference light, L3...object light, L4...object reference light, L5...returned 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, y...signal, Δy...shift width, β...incident angle, θ'...shift angle, θ B …blaze angle, θ S …Tilt angle

Claims

1. A laser light source that emits laser light; a shielding element having an opening through which the laser light passes; an optical modulator that modulates the laser light into a reference light having a different frequency; a light receiving element that receives object light generated by reflection of the laser light on a measurement object and the reference light and outputs a light receiving signal; Equipped with The diameter of the opening is φ ｐｉｎ [mm], 0.10≦φ ｐｉｎ A laser interferometer, characterized in that it satisfies ≦10.

0.

2. 2. The laser interferometer according to claim 1, wherein the laser light incident on the optical modulator is collimated light.

3. the light intensity distribution in a cross section of the collimated light is a Gaussian distribution, When the standard deviation of the Gaussian distribution is σ [mm], the diameter φ of the opening ｐｉｎ [mm] is 0.5σ≦φ ｐｉｎ 3. The laser interferometer according to claim 2, wherein σ satisfies / 2≦3.0σ.

4. The optical axis of the collimated light is a first optical axis, When the reference light or the object light is returned toward the laser light source, the optical axis of the returned light is defined as a second optical axis; A position where the collimated light is generated is defined as a reference position, When the deviation width between the first optical axis and the second optical axis at the reference position is Δy [mm], 4. The laser interferometer according to claim 2, wherein the first optical axis and the second optical axis are shifted so as to satisfy 0.10≦Δy≦10.

0.

5. 5. The laser interferometer according to claim 2, wherein the laser light source is a semiconductor laser element.

6. a collimating lens disposed between the laser light source and the shielding element; The laser interferometer according to claim 5 , wherein the collimating lens collimates the laser light emitted from the laser light source to generate the collimated light.

7. The optical modulator includes a vibration element.

7. The laser interferometer according to claim 1, wherein the optical modulator modulates the laser light by using the vibration element.

8. a demodulation circuit that demodulates a sample signal derived from the object to be measured from the received light signal based on a reference signal; an oscillator circuit that outputs the reference signal to the demodulation circuit; Equipped with 8. The laser interferometer according to claim 7, wherein the vibration element is a signal source of the oscillation circuit.

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