Laser interferometer

Abstract

To realize a laser interferometer easy to downsize, difficult to lower a measuring precision even with disturbances applied, and excellent in usability.SOLUTION: A laser interferometer includes: a laser light source configured to emit laser light; a light splitter configured to split the laser light into first split light and second split light; an optical modulator configured to modulate a frequency of the first split light to generate reference-light; a photodetector configured to receive the reference-light and object-light generated through reflecting the second split light by an object; and a first condenser lens arranged on an optical path of the first split light or an optical path of the second split light and configured to condense incoming light. If the first condenser lens is arranged in the optical path of the first split light, a light diameter of the reference-light in the photodetector is made smaller than a light diameter of the object-light. If the first condenser lens is arranged in the optical path of the second split light, the light diameter of the object-light in the photodetector is made smaller than the light diameter of the reference-light.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a laser vibrometer as a device for measuring the vibration speed of an object. In this laser vibrometer, the object to be measured is irradiated with laser light, and the vibration speed is measured based on the scattered laser light that has received the Doppler shift.

[0003] The laser vibrometer described in Patent Document 1 includes a vibration element that generates a predetermined frequency. This vibration element shifts the frequency of the incident laser light based on its vibration frequency and generates reflected laser light having a frequency different from that of the incident laser light. In the laser vibrometer, this reflected laser light is used as reference light. Then, the light in which the scattered laser light derived from the object to be measured and the reference light are combined is received by a photodetector, and a beat signal is electrically extracted. Then, the vibration speed of the object to be measured is measured from this beat signal.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a laser interferometer such as a laser vibrometer, the scattered laser light (object light) derived from the object to be measured and the reference light are combined and received by a photodetector. At this time, interference occurs in the region where the beam of the object light and the beam of the reference light overlap (overlap region), and it becomes possible to measure the vibration speed of the object and the like.

[0006] However, when forming an overlapping region as described above, it takes time to align (align) each part constituting the interference optical system. This leads to a decrease in the usability of the laser interferometer. In addition, when the alignment is disrupted due to external disturbances such as vibration or shock, the measurement accuracy decreases. On the other hand, it is also conceivable to cancel the influence of external disturbances using a sensor or the like. In that case, there is a concern about an increase in the size and weight of the device.

[0007] Therefore, it has become an issue to realize a laser interferometer that is suppressed in size increase, has a measurement accuracy that is not easily degraded even when an external disturbance is applied, and is excellent in usability.

Means for Solving the Problems

[0008] The laser interferometer according to an application example of the present invention a laser light source that emits laser light, an optical splitter that splits the laser light into a first split light and a second split light, an optical modulator that modulates the frequency of the first split light to generate reference light, a light receiving element that receives object light generated by reflecting the second split light from an object and the reference light, a first condenser lens that is disposed in the optical path of the first split light or the optical path of the second split light and condenses the incident light, and is provided with When the first condenser lens is disposed in the optical path of the first split light, the light diameter of the reference light in the light receiving element is configured to be smaller than the light diameter of the object light, When the first condenser lens is disposed in the optical path of the second split light, the light diameter of the object light in the light receiving element is configured to be smaller than the light diameter of the reference light.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

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Figure 12

Embodiments for Carrying Out the Invention

[0010] Hereinafter, the laser interferometer of the present invention will be described in detail based on the embodiments shown in the accompanying drawings. 1. First Embodiment FIG. 1 is a functional block diagram showing a laser interferometer 1 according to the first embodiment. FIG. 2 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 of FIG. 1.

[0011] In the laser interferometer 1 shown in FIG. 1, the object 14 and the optical modulator 12 shown in FIG. 2 are irradiated with laser light (first split light L1a and second split light L1b). Then, the object light L3 emitted from the object 14 and the reference light L2 emitted from the optical modulator 12 are interfered, and the interference light is received by the light receiving element 10 to obtain a received signal. Then, by the optical heterodyne interference method, a sample signal derived from the object 14 is extracted from the received signal, and based on the sample signal, the displacement and speed of the object 14 are measured.

[0012] The laser interferometer 1 shown in FIG. 1 includes a sensor head unit 51 and a main body unit 59. The sensor head unit 51 shown in FIG. 1 includes an interference optical system 50 and a signal generation unit 60. The sensor head unit 51 is easy to miniaturize and lightweight, and is easy to make portable and easy to install. Therefore, for example, it can be easily arranged near the object 14.

[0013] The main body unit 59 includes a demodulation calculation unit 52. The demodulation calculation unit 52 demodulates a sample signal derived from the object 14 from the received signal. The main body unit 59 shown in FIG. 1 is separated from the sensor head unit 51, but may be integrated with the sensor head unit 51. Also, at least one of the elements included in the sensor head unit 51 shown in FIG. 1 may be included in the main body unit 59.

[0014] 1.1. Interference optical system The interference optical system 50 shown in FIG. 2 is a Michelson type interference optical system. The interference optical system 50 includes a laser light source 2, an optical splitter 4, a light receiving element 10, an optical modulator 12, and a first condenser lens 13.

[0015] The laser light source 2 emits emitted light L1 which is laser light. The emitted light L1 passes through the optical path P1 and enters the optical splitter 4. The optical path refers to the path along which light travels. The optical splitter 4 splits the emitted light L1 into a first split light L1a and a second split light L1b.

[0016] The first split light L1a passes through the optical path P1a and is incident on the optical modulator 12. The optical modulator 12 includes a vibrating element 30, modulates the frequency of the first split light L1a, and generates a reference light L2 which is a laser beam including a modulation signal. The modulation signal is a change in frequency added to the first split light L1a by the optical modulator 12. The reference light L2 passes through the optical path P2 and is incident on the optical splitter 4.

[0017] The second split light L1b passes through the optical path P1b and is incident on the object 14. The second split light L1b incident on the object 14 is reflected as an object light L3 which is a laser beam including a sample signal derived from the object 14. The sample signal is a Doppler signal accompanying the displacement of the object 14 and is a change in frequency added to the second split light L1b. The object light L3 passes through the optical path P3 and is incident on the optical splitter 4.

[0018] The optical splitter 4 mixes the reference light L2 and the object light L3. The mixed reference light L2 passes through the optical path P4 and is incident on the light receiving element 10, and the mixed object light L3 passes through the optical path P4 and is incident on the light receiving element 10. The optical paths P2 and P3 overlap each other in space, and light interference occurs at this overlapping portion. The light receiving element 10 detects the intensity of the light in which the reference light L2 and the object light L3 are mixed, and outputs a light receiving signal corresponding to the intensity.

[0019] In the interference optical system 50 as described above, the phase information of the object 14 is obtained by the optical heterodyne interference method. Specifically, two lights (reference light L2 and object light L3) with slightly different frequencies are interfered, and the phase information is extracted from the obtained interference light. Then, the displacement of the object 14 is obtained from the phase information in a demodulation arithmetic unit 52 described later. In the optical heterodyne interference method, when extracting the phase information from the interference light, it is less affected by stray light and the like that become noise.

[0020] 1.1.1. Laser light source The laser light source 2 is a laser light source that emits injection light L1 (laser light) having coherence. As the laser light source 2, a light source with a line width of MHz band or less is preferably used. Specifically, gas lasers such as He-Ne lasers, DFB-LDs (Distributed FeedBack - Laser Diodes), FBG-LDs (Fiber Bragg Grating Laser Diodes), VCSELs (Vertical Cavity Surface Emitting Laser Diodes), and semiconductor laser elements such as FP-LDs (Fabry-Perot Laser Diodes) can be mentioned.

[0021] The laser light source 2 is particularly preferably a semiconductor laser element. Thereby, it becomes possible to particularly miniaturize the laser light source 2. For this reason, the laser interferometer 1 can be miniaturized.

[0022] The injection light L1 emitted from the laser light source 2 enters the optical splitter 4 while the light diameter expands at a predetermined divergence angle as shown in FIG. 2 due to the influence of optical diffraction or the like. An optical element for adjusting the divergence angle may be arranged between the laser light source 2 and the optical splitter 4 as necessary.

[0023] 1.1.2. Optical Splitter The optical splitter 4 shown in FIG. 2 is a non-polarizing beam splitter or a non-polarized beam splitter that splits the injection light L1 at a predetermined ratio. As an example, the optical splitter 4 shown in FIG. 2 reflects a part of the injection light L1 to generate a first split light L1a and transmits the other part of the injection light L1 to generate a second split light L1b. Since a non-polarizing beam splitter or a non-polarized beam splitter does not require a wavelength plate or the like for controlling polarization, it contributes to reducing the number of optical elements constituting the interference optical system 50.

[0024] In addition, the optical splitter 4 has a function of mixing the incident reference light L2 and object light L3. When the reference light L2 is incident on the optical splitter 4 shown in FIG. 2, a part of the light quantity is transmitted. When the object light L3 is incident on the optical splitter 4 shown in FIG. 2, a part of the light quantity is reflected. A part of the reference light L2 and a part of the object light L3 are mixed and incident on the light receiving element 10 as mixed light.

[0025] Examples of the type of the optical splitter 4 include, in addition to the cube type element shown in FIG. 2, a plate type element, a stacked type element, and the like. Among these, from the viewpoint of suppressing the optical path difference between the reference light L2 and the object light L3, the cube type element is preferably used.

[0026] 1.1.3. Light receiving element The light receiving element 10 outputs a photocurrent (light receiving signal) corresponding to the intensity of the mixed light. Examples of the light receiving element 10 include a photodiode, a phototransistor, and the like. Note that the light received by the light receiving element 10 may be light including a sample-derived component and a modulation component, and is not limited to the interference light between the reference light L2 including the modulation component as described above and the object light L3 including the sample-derived component. In addition, "demodulating the sample signal from the light receiving signal" in this specification includes demodulating the sample signal from various signals converted from the photocurrent (light receiving signal).

[0027] 1.1.4. Optical modulator Next, the optical modulator 12 including the vibration element 30 will be described.

[0028] The optical modulator 12 shown in FIG. 2 has a vibration element 30. The vibration element 30 performs thickness shear vibration at a predetermined mechanical resonance frequency and has a diffraction grating (not shown). When the first divided light L1a is irradiated on this diffraction grating, diffracted light with a shifted frequency is generated, and the reference light L2 including the modulation signal is obtained.

[0029] Note that the first divided light L1a shown in FIG. 2 propagates while expanding (diverging) the light diameter at a predetermined divergence angle. Therefore, the reference light L2 is also incident on the optical splitter 4 while diverging at the same divergence angle.

[0030] Examples of the vibration element 30 include a crystal oscillator, a silicon oscillator, a ceramic oscillator, a piezo element, etc. Among these, the vibration element 30 is preferably a crystal oscillator, a silicon oscillator, or a ceramic oscillator. These oscillators are different from other oscillators, such as piezo elements, etc., and are oscillators that utilize the mechanical resonance phenomenon. Therefore, they have a high Q value and can easily achieve stabilization of the natural frequency.

[0031] Also, according to the optical modulator 12 having the vibration element 30, the volume and weight can be significantly reduced compared to, for example, an optical modulator having an acousto-optic modulator (AOM) or an electro-optic modulator (EOM). For this reason, miniaturization, weight reduction, and low power consumption of the laser interferometer 1 can be achieved. Note that if these effects do not need to be obtained, the above optical modulator 12 may be replaced with an optical modulator using an AOM or an EOM.

[0032] Examples of the optical modulator 12 include the optical modulator disclosed in Japanese Patent Application Laid-Open No. 2022-38156. This publication mentions a crystal AT oscillator as the vibration element 30. Also, an SC-cut crystal oscillator, a tuning fork type crystal oscillator, a surface acoustic wave element of a crystal, etc. may be used for the vibration element 30.

[0033] A silicon oscillator is an oscillator including a single-crystal silicon piece manufactured from a single-crystal silicon substrate using MEMS technology and a piezoelectric film. MEMS (Micro Electro Mechanical Systems) refers to a micro electro mechanical system. Examples of the shape of the single-crystal silicon piece include a cantilever shape such as a two-pronged tuning fork type or a three-pronged tuning fork type, and a double-cantilever shape. The oscillation frequency of the silicon oscillator is, for example, about 1 kHz to several 100 MHz.

[0034] A ceramic resonator is a resonator comprising a piezoelectric ceramic piece manufactured by firing piezoelectric ceramics and an electrode. Examples of the piezoelectric ceramics include lead zirconate titanate (PZT), barium titanate (BTO), and the like. The oscillation frequency of the ceramic resonator is, for example, about several 100 kHz to several 10 MHz.

[0035] Among these, a crystal resonator is preferably used for the vibration element 30. Since the crystal itself is a piezoelectric material, the crystal resonator has particularly high frequency stability.

[0036] 1.1.5. First condenser lens The first condenser lens 13 shown in FIG. 2 is disposed at an overlapping portion of the optical path P1b of the second split light L1b and the optical path P3 of the object light L3. The first condenser lens 13 has a function of condensing the incident second split light L1b and object light L3. By disposing the first condenser lens 13 in the optical path P1b, the divergence angle of the emitted second split light L1b can be suppressed as compared with the divergence angle of the incident second split light L1b. In the example of FIG. 2, the second split light L1b collimated so that the divergence angle becomes substantially zero is generated. The collimated second split light L1b is irradiated onto the object 14 while maintaining the optical path. Further, thereby, the object light L3 formed by reflecting the second split light L1b by the object 14 also becomes collimated light. Then, the collimated object light L3 is incident on the first condenser lens 13 while maintaining the optical path.

[0037] In this way, by providing the first condenser lens 13 in the optical path P1b of the second split light L1b, it becomes easier to maintain the optical paths of the second split light L1b and the object light L3. Therefore, even if the working distance (the distance between the first condenser lens 13 and the object 14) changes, the irradiation range of the second split light L1b with respect to the object 14 can be made constant. As a result, it is possible to suppress a decrease in measurement accuracy due to fluctuations in the irradiation range. In addition, by providing the first condenser lens 13, it is possible to suppress a significant expansion of the optical path of the object light L3 incident on the first condenser lens 13. If the optical path of the object light L3 expands significantly, it will cause a decrease in the amount of light of the object light L3 incident on the first condenser lens 13. Therefore, if a significant expansion of the optical path of the object light L3 can be suppressed, a decrease in the S / N ratio (signal-to-noise ratio) can be suppressed.

[0038] Any optical component having the above functions can be used for the first condenser lens 13. For example, an optical component called a collimating lens is used. Examples of the collimating lens include a plano-convex aspherical lens. In addition, the first condenser lens 13 may be composed of a plurality of optical elements.

[0039] Note that the object light L3 incident on the first condenser lens 13 is focused by the above function of the first condenser lens 13 and is incident on the optical splitter 4.

[0040] As described above, the reference light L2 is incident on the optical splitter 4 while diverging, and the object light L3 is incident on the optical splitter 4 while converging. Then, a part of the reference light L2 and a part of the object light L3 are mixed in the optical path P4 and reach the light receiving element 10 while passing through the same space. In the optical path P4, the reference light L2 and the object light L3 interfere with each other, and a mixed light including an interference signal (beat signal) is generated.

[0041] FIG. 3 is a conceptual diagram for explaining the effect brought about by the first condenser lens 13 shown in FIG. 2. FIG. 3 shows images of the light intensity distributions when the positions of the optical paths P2 and P3 shift due to disturbances, both when the first condenser lens 13 is absent and when it is present. In this image, the horizontal axis indicates the optical paths and positions of the reference light L2 and the object light L3, and the vertical axis indicates the light intensity. Therefore, each curve in FIG. 3 shows the light intensity distribution of the reference light L2 and the object light L3.

[0042] When the positions of the optical paths P2 and P3 shift, the position reaching the light receiving element 10 also shifts. Then, the region (interference region IF) where the beam of the reference light L2 and the beam of the object light L3 overlap and interfere becomes smaller according to the amount of shift. The size of the interference region IF and the light intensity in the interference region IF are reflected in the S / N ratio (signal-to-noise ratio) of the received signal.

[0043] When there is no first condenser lens 13, like the reference light L2, the object light L3 is also incident on the optical splitter 4 while diverging. Therefore, the optical path of the reference light L2 and the optical path of the object light L3 at the light receiving element 10 become about the same and large. In this case, even a slight position shift is strongly reflected in the S / N ratio (signal-to-noise ratio) of the received signal. Specifically, since the optical paths are about the same, the interference region IF becomes smaller according to the amount of shift. As a result, the interference signal becomes smaller and the S / N ratio of the received signal decreases. Also, the light intensity distributions of the reference light L2 and the object light L3 have a Gaussian distribution shape as shown in FIG. 3, for example. Then, the influence of the position shift is easily reflected in the interference signal, leading to a decrease in the S / N ratio of the received signal. Therefore, when there is no first condenser lens 13, the position shift of the optical paths P2 and P3 is likely to lead to a decrease in the S / N ratio of the received signal. For these reasons, the disturbance resistance is lowered, and the difficulty of aligning the interference optical system 50 also increases.

[0044] On the one hand, when the first condenser lens 13 is arranged in the overlapping portion of the optical path P1b and the optical path P3, in the light receiving element 10, the optical path of the object light L3 can be made smaller than that of the reference light L2. In this case, even if there is a slight misalignment, a sufficient interference region IF can be secured. That is, since the optical path of the object light L3 is smaller than that of the reference light L2, even if misalignment occurs in the optical paths P2 and P3, the overlap of the beams is maintained. As a result, a decrease in the S / N ratio of the received signal can be suppressed. Therefore, by providing the first condenser lens 13, the disturbance resistance (robustness) of the measurement accuracy can be enhanced. That is, a laser interferometer 1 in which the measurement accuracy is not easily degraded even when a disturbance is applied can be realized.

[0045] Also, since the optical paths of the reference light L2 and the object light L3 are different, interference is likely to occur even if there is misalignment in the optical paths P2 and P3. For this reason, when aligning the interference optical system 50 before or during measurement, it becomes easier to acquire an interference signal, and the work can be performed based on the intensity of the interference signal as a guide. Therefore, a laser interferometer 1 in which the alignment of the interference optical system 50 is easy and the usability is excellent can be realized.

[0046] In the laser interferometer 1 shown in FIG. 2, the above effects are realized by the arrangement of the first condenser lens 13. Since the first condenser lens 13 is sufficiently small and lightweight, it can contribute to the miniaturization of the laser interferometer 1. Also, since the laser interferometer 1 does not require a feedback mechanism for detecting a disturbance and reflecting it in the measurement, miniaturization and weight reduction are also easy to achieve from this perspective.

[0047] In the example of FIG. 2, the first condenser lens 13 is configured such that the first split light L1a emitted from the first condenser lens 13 becomes collimated light. On the other hand, the first condenser lens 13 may be configured such that the first split light L1a emitted from the first condenser lens 13 converges. In that case, it is preferable to arrange the object 14 near the focal point of the first split light L1a.

[0048] 1.2. Signal generation unit The signal generation unit 60 shown in FIG. 1 outputs a drive signal input to the vibration element 30 and a reference signal input to the demodulation calculation unit 52.

[0049] The signal generation unit 60 shown in FIG. 1 includes an oscillation circuit 61. The oscillation circuit 61 drives the vibration element 30 at a predetermined frequency (outputs a drive signal to the vibration element 30) and outputs a reference signal. The vibration element 30 is driven by the drive signal and adds a modulation signal to the first divided light L1a. Then, the demodulation calculation unit 52 demodulates the received light signal including this modulation signal based on the reference signal. Therefore, even if disturbances are added to the modulation signal and the reference signal respectively, the influence of the disturbance can be canceled or reduced in the demodulation calculation unit 52. Thereby, the laser interferometer 1 capable of more accurate measurement can be realized.

[0050] Examples of the oscillation circuit 61 include the oscillation circuit disclosed in Japanese Patent Application Laid-Open No. 2022-38156, but an oscillation circuit having other configurations may also be used.

[0051] Alternatively, the signal generation unit 60 may include a signal generator such as a function generator or a signal generator instead of the oscillation circuit 61.

[0052] 1.3. Demodulation Calculation Unit The demodulation calculation unit 52 shown in FIG. 1 includes a preprocessing unit 53, a demodulation processing unit 54, and a demodulated signal output unit 55. The functions exhibited by these functional units are realized by hardware including, for example, a processor, a memory, an external interface, an input unit, a display unit, etc. Specifically, it is realized by the processor reading and executing a program stored in the memory. Note that these components can communicate with each other via an external bus.

[0053] Examples of the processor include a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. Instead of the above-mentioned processors executing software, a method in which an FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), etc. realize the above-mentioned functions may be adopted.

[0054] Examples of the memory include an HDD (Hard Disk Drive), an SSD (Solid State Drive), an EEPROM (Electrically Erasable Programmable Read-Only Memory), a ROM (Read-Only Memory), a RAM (Random Access Memory), etc.

[0055] Examples of the external interface include digital input / output ports such as a USB (Universal Serial Bus), an Ethernet (registered trademark) port, a wireless LAN (Local Area Network), Bluetooth (registered trademark), etc.

[0056] Examples of the input unit include various input devices such as a keyboard, a mouse, a touch panel, a touch pad, etc. Examples of the display unit include a liquid crystal display panel, an organic EL (Electro Luminescence) display panel, etc.

[0057] Note that the external interface, the input unit, and the display unit may be provided as necessary and may be omitted.

[0058] For example, the preprocessing unit 53 and the demodulation processing unit 54 can apply the preprocessing unit and the demodulation unit disclosed in Japanese Patent Application Laid-Open No. 2022-38156.

[0059] The preprocessing unit 53 performs preprocessing on the received signal based on the reference signal. The preprocessing refers to a process of performing calculations on the received signal based on the reference signal to generate a signal (preprocessed signal) to which a known quadrature detection method can be applied.

[0060] The demodulation processing unit 54 demodulates a sample signal derived from the object 14 based on the reference signal from the preprocessed signal output from the preprocessing unit 53, for example, by the quadrature detection method.

[0061] The demodulated signal output unit 55 performs phase connection such as unwrapping processing on the sample signal, specifically, the phase information derived from the object 14, to calculate the displacement of the object 14. In this case, a displacement meter equipped with the laser interferometer 1 can be obtained. Also, the speed can be calculated from the displacement, and in this case, a speed meter equipped with the laser interferometer 1 can be obtained.

[0062] 2. Second Embodiment FIG. 4 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the second embodiment.

[0063] Hereinafter, the second embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 4, the same components as those in the first embodiment are denoted by the same reference numerals.

[0064] The interference optical system 50 shown in FIG. 4 is the same as the interference optical system 50 shown in FIG. 2 except that the positions of the optical modulator 12 and the object 14 with respect to the optical splitter 4 are interchanged.

[0065] That is, the first condenser lens 13 shown in FIG. 4 is disposed in the overlapping portion of the optical path P1a of the first split light L1a and the optical path P2 of the reference light L2. Also, in FIG. 4, the light transmitted through the optical splitter 4 is taken as the first split light L1a, and the light reflected by the optical splitter 4 is taken as the second split light L1b.

[0066] The first split light L1a shown in FIG. 4 is focused when passing through the first condenser lens 13 and is incident on the optical modulator 12 as, for example, collimated light. The reference light L2 generated by the optical modulator 12 is focused when passing through the first condenser lens 13 and is incident on the optical splitter 4. Then, it is reflected by the optical splitter 4 and mixed with the object light L3.

[0067] The second split light L1b shown in FIG. 4 is incident on the object 14 while diverging. The object light L3 generated by the object 14 is incident on the optical splitter 4. Then, it passes through the optical splitter 4 and is mixed with the reference light L2.

[0068] Also in the second embodiment as described above, the same effects as those of the first embodiment can be obtained. That is, the first condenser lens 13 shown in FIG. 4 is configured such that the optical path of the reference light L2 in the light receiving element 10 is smaller than the optical path of the object light L3. Thereby, miniaturization is facilitated, the measurement accuracy is less likely to decrease even when a disturbance is applied, and the laser interferometer 1 with excellent usability can be realized.

[0069] 3. Third Embodiment FIG. 5 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the third embodiment.

[0070] Hereinafter, the third embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 5, the same components as those in the first embodiment are denoted by the same reference numerals.

[0071] The interference optical system 50 shown in FIG. 5 is the same as the interference optical system 50 shown in FIG. 2 except that the light receiving element 10 is arranged at a predetermined position in the optical path P4.

[0072] In the interference optical system 50 shown in FIG. 5, the focal point FC1 of the first condenser lens 13 is located on the optical path P4. This focal point FC1 refers to the focal point where the light transmitted through the first condenser lens 13 and reflected by the optical splitter 4 converges. And the light receiving element 10 shown in FIG. 5 is arranged farther from the focal point FC1 than the optical splitter 4. According to such a configuration, the angular difference between the light rays included in the reference light L2 reaching the light receiving element 10 and the light rays included in the object light L3 can be reduced compared to the interference optical system 50 shown in FIG. 2. Note that the "light ray" in this specification refers to the optical path of light per unit area of the cross section.

[0073] FIG. 6 is a conceptual diagram for explaining the effect brought about by the arrangement of the light receiving element 10 shown in FIG. 5. In FIG. 6, when the light receiving element 10 is arranged closer to the focal point FC1 (on the side of the optical splitter 4 from the focal point FC1) as shown in FIG. 2, and when the light receiving element 10 is arranged farther from the focal point FC1 (on the side opposite to the optical splitter 4 from the focal point FC1) as shown in FIG. 5, images are shown in which the light rays L20 included in the reference light L2 and the light rays L30 included in the object light L3 are represented by arrows, respectively. In this image, it is assumed that the aggregate (bundle) of a plurality of light rays L20 is the reference light L2, and the aggregate (bundle) of a plurality of light rays L30 is the object light L3.

[0074] When the light receiving element 10 is arranged closer to the focal point FC1, the reference light L2 reaches the light receiving element 10 while diverging, whereas the object light L3 reaches the light receiving element 10 while converging. For this reason, the light rays L20 and the light rays L30 intersect on the light receiving surface of the light receiving element 10, and interference fringes (bright and dark fringes) are formed on the light receiving surface. Depending on the intersection angle, the interference signal is averaged due to the influence of light and dark, leading to a decrease in the S / N ratio of the received signal.

[0075] On the other hand, when the light-receiving element 10 is disposed farther from the focal point FC1, not only the reference light L2 (the light that has not passed through the first condenser lens 13) but also the object light L3 (the light focused by the first condenser lens 13) reaches the light-receiving element 10 while diverging. For this reason, the light rays L20 and L30 approach a state where they are parallel to each other, and even if they intersect on the light-receiving surface of the light-receiving element 10, the intersection angle can be made sufficiently small. Thereby, generation of interference fringes can be suppressed, or even if they are generated, the period of light and dark can be lengthened. As a result, a decrease in the S / N ratio of the received signal due to the interference fringes can be suppressed. In the following description, a state where the light rays L20 and L30 approach parallel is referred to as "a high relative parallelism of the light rays". Also in the third embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0076] 4. Fourth Embodiment FIG. 7 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the fourth embodiment.

[0077] Hereinafter, the fourth embodiment will be described. In the following description, the differences from the third embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 7, the same components as those in the third embodiment are denoted by the same reference numerals.

[0078] The interference optical system 50 shown in FIG. 7 is the same as that in the third embodiment except that a second condenser lens 15 is disposed in the optical path P4.

[0079] In the interference optical system 50 shown in FIG. 7, a second condenser lens 15 is disposed between the focal point FC1 and the light-receiving element 10. The second condenser lens 15 has a function of condensing the incident reference light L2 and object light L3. By disposing the second condenser lens 15 in the optical path P4, the reference light L2, which is divergent light, can be focused and the divergence angle can be suppressed. In the example of FIG. 7, it is collimated so that the divergence angle becomes substantially zero. On the other hand, the second condenser lens 15 also focuses the object light L3 that has passed through the focal point FC1 and has become divergent light. In the example of FIG. 7, it is collimated so that the divergence angle becomes substantially zero.

[0080] FIG. 8 is a conceptual diagram for explaining the effect brought about by the second condenser lens 15 shown in FIG. 7. FIG. 8 shows an image in which the light rays L20 included in the reference light L2 and the light rays L30 included in the object light L3 shown in FIG. 7 are each represented by an arrow.

[0081] By disposing the second condenser lens 15 between the focal point FC1 and the light receiving element 10, for example, the reference light L2 and the object light L3 can be collimated respectively. Thereby, the expansion of the optical path diameter of the reference light L2 and the optical path diameter of the object light L3 in the light receiving element 10 can be suppressed. As a result, the light receiving element 10 can be miniaturized and the laser interferometer 1 can be miniaturized accordingly. Also, in the light rays L20 and L30, the relative parallelism can be enhanced. Thereby, a decrease in the S / N ratio of the received signal due to interference fringes can be particularly suppressed.

[0082] As the second condenser lens 15, any optical component having the above-described function can be used. For example, an optical component called a collimating lens is used. Examples of the collimating lens include a plano-convex aspherical lens. Also, the second condenser lens 15 may be composed of a plurality of optical elements. Also, in this embodiment, the same effects as those of the first embodiment can be obtained.

[0083] 5. Fifth Embodiment FIG. 9 is a schematic configuration diagram showing an interference optical system 50 provided in the laser interferometer 1 according to the fifth embodiment.

[0084] Hereinafter, the fifth embodiment will be described. In the following description, the differences from the third embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 9, the same components as those in the third embodiment are denoted by the same reference numerals.

[0085] The interference optical system 50 shown in FIG. 9 is the same as that of the third embodiment except that it includes a light intensity distribution adjuster 16 disposed in the optical path P4.

[0086] In the interference optical system 50 shown in FIG. 9, an optical intensity distribution adjuster 16 is disposed between the optical splitter 4 and the focal point FC1. The optical intensity distribution adjuster 16 has a function of adjusting the optical intensity distribution of the incident reference light L2 and object light L3. The optical intensity distribution adjuster 16 shown in FIG. 9 has an aspherical lens 161. The function of the optical intensity distribution adjuster 16 is determined according to, for example, the aspherical shape of the aspherical lens 161.

[0087] FIG. 10 is a cross-sectional view for explaining the operation of the aspherical lens 161 shown in FIG. 9. The aspherical lens 161 shown in FIG. 10 has a convex portion 162 on the outer periphery and a concave portion 163 in the center. The convex portion 162 is a convex lens and has a function of focusing the incident light. The concave portion 163 is a concave lens and has a function of diverging the incident light. In the example of FIG. 10, the interference optical system 50 is configured such that the reference light L2 is incident on the convex portion 162 and the object light L3 is incident on the concave portion 163. Since the reference light L2 incident on the convex portion 162 is divergent light, the divergence is suppressed when passing through the convex portion 162. Thereby, the reference light L2 can be collimated. On the other hand, since the optical intensity distribution adjuster 16 shown in FIG. 10 is disposed on the optical splitter 4 side rather than the focal point FC1, the object light L3 enters the concave portion 163 while converging. For this reason, the focusing of the object light L3 is suppressed when passing through the concave portion 163. Thereby, the object light L3 can be collimated. Therefore, by using the optical intensity distribution adjuster 16 shown in FIG. 10, both the reference light L2 and the object light L3 can be collimated.

[0088] According to such a configuration, it is possible to suppress an increase in the optical path diameter of the reference light L2 and the optical path diameter of the object light L3 in the light receiving element 10. As a result, it is possible to reduce the size of the light receiving element 10 and thereby reduce the size of the laser interferometer 1. Also, similar to the fourth embodiment, it is possible to particularly suppress a decrease in the S / N ratio of the received signal due to interference fringes. Also, in this embodiment, the same effects as those of the first embodiment can be obtained.

[0089] 6. Sixth Embodiment FIG. 11 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the sixth embodiment.

[0090] Hereinafter, the sixth embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 11, the same components as those in the first embodiment are denoted by the same reference numerals.

[0091] The interference optical system 50 shown in FIG. 11 is the same as that in the first embodiment except that the optical path P1a and the optical path P2 are non-coaxial, and the optical path P1b and the optical path P3 are non-coaxial.

[0092] That is, in the interference optical system 50 shown in FIG. 11, the posture of the optical modulator 12 with respect to the optical splitter 4 is set so that the optical path P1a and the optical path P2 are displaced. Also, the posture of the object 14 with respect to the optical splitter 4 is set so that the optical path P1b and the optical path P3 are displaced.

[0093] In this case, the first split light L1a emitted from the optical splitter 4 passes through the optical path P1a and enters the optical modulator 12. Then, the reference light L2 generated by the optical modulator 12 passes through the optical path P2 which is displaced from the optical path P1a and enters the optical splitter 4. Then, the reference light L2 passes through the optical splitter 4 and is mixed with the object light L3 on the optical path P4.

[0094] Also, the second split light L1b emitted from the optical splitter 4 passes through the optical path P1b, passes through the first condenser lens 13, and enters the object 14. Then, the object light L3 generated by the object 14 passes through the optical path P3 which is displaced from the optical path P1b and enters the optical splitter 4. At this time, since the optical path P3 is displaced from the optical path P1b, the object light L3 enters the optical splitter 4 without passing through the first condenser lens 13. Then, the object light L3 is reflected by the optical splitter 4 and mixed with the reference light L2 on the optical path P4.

[0095] According to such a configuration, object light L3, which is, for example, collimated by the first condenser lens 13, can reach the light receiving element 10 without being focused by the first condenser lens 13. Therefore, in this embodiment, compared with the case where the object light L3 passes through the first condenser lens 13, the relative parallelism of the light rays can be increased. As a result, the generation of interference fringes can be suppressed, or even if they are generated, the period of light and dark can be lengthened, and a decrease in the S / N ratio of the received signal due to the interference fringes can be suppressed.

[0096] From the perspective of not allowing the object light L3 to enter the first condenser lens 13, the distance Δx between the center of the optical path P1b of the second split light L1b (the central axis of the first condenser lens 13) and the center of the optical path P3 of the object light L3 (the light that is emitted from the first condenser lens 13, passes through the object 14, and then travels toward the first condenser lens 13) at the position of the first condenser lens 13 preferably satisfies the following formula. (Φlen + Φco) / 2 < Δx

[0097] In the above formula, Φlen is the effective diameter of the first condenser lens 13, and Φco is the optical diameter of the object light L3 (the light traveling toward the first condenser lens 13). By the distance Δx satisfying the above formula, it is possible to suppress the object light L3 from entering the first condenser lens 13. As a result, it is possible to prevent the object light L3 from being inadvertently focused.

[0098] Also, in this embodiment as well, the same effects as those of the first embodiment, that is, the measurement accuracy is less likely to decrease even when an external disturbance is applied, and the effect that alignment is easy can be obtained. As a result, a laser interferometer 1 with high disturbance resistance and excellent usability can be obtained.

[0099] In this embodiment, the non - coaxialization of the optical path as described above is realized by tilting the postures of the optical modulator 12 and the light receiving element 10 with respect to the optical splitter 4. However, the means for realizing the non - coaxialization of the optical path is not limited to this. For example, by adding an optical splitter or a mirror (not shown), the non - coaxialization of the optical path may be realized without tilting the optical modulator 12 or the light receiving element 10.

[0100] Also, in the present embodiment, although the first condenser lens 13 is disposed on the optical path P1b, the first condenser lens 13 may be disposed on the optical path P1a. In this case, the first split light L1a emitted from the optical splitter 4 passes through the optical path P1a, transmits through the first condenser lens 13, and enters the optical modulator 12. The reference light L2 enters the optical splitter 4 without passing through the first condenser lens 13. In the mixed light passing through the optical path P4, although the positions of the reference light L2 and the object light L3 are reversed from those in FIG. 11, the same effects as those of the present embodiment can be obtained.

[0101] 7. Seventh Embodiment FIG. 12 is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the seventh embodiment.

[0102] Hereinafter, the seventh embodiment will be described. In the following description, the differences from the first embodiment will be mainly described, and the description of the same matters will be omitted. In FIG. 12, the same components as those in the first embodiment are denoted by the same reference numerals.

[0103] The interference optical system 50 shown in FIG. 12 is the same as the interference optical system 50 shown in FIG. 2, except that the optical splitter 4 is a polarization beam splitter and the light receiving element 10 is composed of a differential amplification type light receiving module.

[0104] The optical splitter 4 shown in FIG. 12 is a polarization beam splitter and has a function of reflecting S-polarized light and transmitting P-polarized light. Specifically, the optical splitter 4 shown in FIG. 12 splits the emitted light L1 into a first split light L1a that is S-polarized light and a second split light L1b that is P-polarized light. With this function, in the optical splitter 4 shown in FIG. 12, it is easy to suppress the light quantity loss when splitting the emitted light L1 into two. Thereby, a decrease in the S / N ratio of the received signal due to the light quantity loss can be suppressed.

[0105] On the optical path P1 between the laser light source 2 and the optical splitter 4 shown in FIG. 12, a half-wave plate 41 is disposed. The emitted light L1 emitted from the laser light source 2 is transmitted through the half-wave plate 41, and is converted into linearly polarized light with an intensity ratio of S-polarized light to P-polarized light of, for example, 50:50.

[0106] On the optical path P1a between the optical splitter 4 and the optical modulator 12 shown in FIG. 12, a quarter-wave plate 42 is disposed. The first split light L1a, which is S-polarized light, emitted from the optical splitter 4 is converted into circularly polarized light by the quarter-wave plate 42. This circularly polarized light is incident on the optical modulator 12 and becomes the reference light L2.

[0107] On the optical path P2 between the optical modulator 12 and the optical splitter 4 shown in FIG. 12, a quarter-wave plate 42 is disposed. The reference light L2 passes through the optical path P2, is converted into P-polarized light by the quarter-wave plate 42, and is incident on the optical splitter 4. Then, the reference light L2 passes through the optical splitter 4 and is mixed with the object light L3 on the optical path P4.

[0108] On the optical path P1b between the optical splitter 4 and the object 14 shown in FIG. 12, a first condenser lens 13 and a quarter-wave plate 43 are disposed. The second split light L1b, which is P-polarized light, emitted from the optical splitter 4 is focused by the first condenser lens 13 and, for example, collimated. The collimated second split light L1b is converted into circularly polarized light by the quarter-wave plate 43. This circularly polarized light is incident on the object 14 and becomes the object light L3.

[0109] On the optical path P3 between the object 14 and the optical splitter 4 shown in FIG. 12, a quarter-wave plate 43 and a first condenser lens 13 are disposed. The object light L3 passes through the optical path P3, is converted into S-polarized light by the quarter-wave plate 43. The object light L3 converted into S-polarized light is focused by the first condenser lens 13. Then, the object light L3 is reflected by the optical splitter 4 and is mixed with the reference light L2 on the optical path P4.

[0110] In the optical path P4, a half-wave plate 44 is disposed. When the mixed light passes through the half-wave plate 44, the polarization states are aligned. Thereby, interference occurs between the reference light L2 and the object light L3, and the mixed light including the interference signal is incident on the light receiving element 10.

[0111] As described above, the light receiving element 10 shown in FIG. 12 is composed of a differential amplification type light receiving module. The light receiving element 10 shown in FIG. 12 includes a first PD 101, a second PD 102, and a PBS 103. The first PD 101 and the second PD 102 are each a photodiode or the like. Further, a polarization beam splitter is preferably used for the PBS 103. The mixed light incident on the light receiving element 10 is split into S-polarized light and P-polarized light by the PBS 103. The P-polarized light is received by the first PD 101, and the S-polarized light is received by the second PD 102. By using such a differential amplification type light receiving module as the light receiving element 10, noise included in the mixed light of the reference light L2 and the object light L3 can be canceled or reduced, and the S / N ratio of the received signal can be particularly increased. Note that in the light receiving element 10, each optical element does not have to be modularized. Further, from the viewpoint of making the optical path difference zero between the optical path on the first PD 101 side and the optical path on the second PD 102 side, the PBS 103 is preferably a cube type element. Also in the seventh embodiment as described above, the same effects as those of the first embodiment can be obtained.

[0112] 8. Effects Exhibited by the Embodiment As described above, the laser interferometer 1 according to the embodiment includes a laser light source 2, an optical splitter 4, an optical modulator 12, a light receiving element 10, and a first condenser lens 13. The laser light source 2 emits an emitted light L1 (laser light). The optical splitter 4 splits the emitted light L1 into a first split light L1a and a second split light L1b. The optical modulator 12 modulates the frequency of the first split light L1a to generate a reference light L2. The light receiving element 10 receives an object light L3 generated by reflecting the second split light L1b by the object 14 and the reference light L2. The first condenser lens 13 is disposed on the optical path P1a of the first split light L1a or the optical path P1b of the second split light L1b to condense the incident light. When the first condenser lens 13 is disposed on the optical path P1a of the first split light L1a, the light diameter of the reference light L2 at the light receiving element 10 is configured to be smaller than the light diameter of the object light L3. When the first condenser lens 13 is disposed on the optical path P1b of the second split light L1b, the light diameter of the object light L3 at the light receiving element 10 is configured to be smaller than the light diameter of the reference light L2.

[0113] According to such a configuration, the light diameter of either the reference light L2 or the object light L3 becomes relatively small, and it becomes easy to secure a region where both overlap and interfere. Also, even when a disturbance such as vibration or shock is applied, the interference state is easily maintained, so that the S / N ratio of the received signal is less likely to decrease. Further, the first condenser lens 13 is sufficiently small and lightweight, and a feedback mechanism or the like for detecting a disturbance and reflecting it in the measurement is not required. Therefore, according to the above configuration, it is possible to realize a laser interferometer 1 that is easy to miniaturize, has high measurement accuracy even when a disturbance is applied, and is excellent in usability.

[0114] In the laser interferometer 1 according to the embodiment, when the focal point FC1 of the first condenser lens 13 is placed on the optical path connecting the first condenser lens 13 and the light receiving element 10 via the optical splitter 4, the light receiving element 10 is disposed farther from the optical splitter 4 than the focal point FC1.

[0115] According to such a configuration, not only the reference light L2 (the light that has not passed through the first condenser lens 13) but also the object light L3 (the light focused by the first condenser lens 13) reaches the light receiving element 10 while diverging. Thereby, the relative parallelism of the light rays is increased, and a decrease in the S / N ratio of the light reception signal due to interference fringes can be suppressed.

[0116] Further, in the laser interferometer 1 according to the embodiment, the first condenser lens 13 is disposed on the optical path P1b of the second split light L1b.

[0117] According to such a configuration, it becomes easy to maintain the optical paths of the second split light L1b and the object light L3. Therefore, even if the working distance (the distance between the first condenser lens 13 and the object 14) changes, the irradiation range of the second split light L1b with respect to the object 14 can be made constant. Thereby, a decrease in the measurement accuracy due to fluctuations in the irradiation range can be suppressed. In addition, a significant expansion of the optical path of the object light L3 incident on the first condenser lens 13 can be suppressed. When the optical path of the object light L3 significantly expands, it causes a decrease in the amount of the object light L3 incident on the first condenser lens 13. Therefore, if a significant expansion of the optical path of the object light L3 can be suppressed, a decrease in the S / N ratio of the light reception signal can be suppressed.

[0118] Further, in the laser interferometer 1 according to the embodiment, the first condenser lens 13 is a collimating lens.

[0119] According to such a configuration, since the optical paths of the light irradiated to the optical modulator 12 and the object 14 are easily maintained, the irradiation ranges of these lights can be made constant and a significant expansion of the optical path can be suppressed. Thereby, a decrease in the S / N ratio of the light reception signal can be suppressed.

[0120] Further, in the laser interferometer 1 according to the above embodiment, when the first condenser lens 13 is disposed in the optical path P1a of the first split light L1a, the first split light L1a is configured to pass through the first condenser lens 13, and the reference light L2 is configured not to pass through the first condenser lens 13. Further, when the first condenser lens 13 is disposed in the optical path P1b of the second split light L1b, the second split light L1b is configured to pass through the first condenser lens 13, and the object light L3 is configured not to pass through the first condenser lens 13. When the effective diameter of the first condenser lens 13 is Φlen, the optical diameter of the light that is emitted from the first condenser lens 13 and travels through the optical modulator 12 or the object 14 and then travels toward the first condenser lens 13 is Φco, and the distance between the central axis of the first condenser lens 13 and the center of the optical path of the light traveling toward the first condenser lens 13 at the position of the first condenser lens 13 is Δx, then (Φlen + Φco) / 2 < Δx is satisfied.

[0121] According to such a configuration, it is possible to suppress the light traveling toward the first condenser lens 13 after passing through the optical modulator 12 or the object 14 from entering the first condenser lens 13. Thereby, it is possible to suppress this light from being unintentionally focused.

[0122] Further, the laser interferometer 1 according to the above embodiment includes a second condenser lens 15 that is disposed in the optical path P4 connecting the optical splitter 4 and the light receiving element 10 and that condenses the incident light.

[0123] According to such a configuration, for example, in the optical path P4, the reference light L2 and the object light L3 can be collimated respectively. Thereby, it is possible to suppress the expansion of the optical diameter of the reference light L2 and the optical diameter of the object light L3 at the light receiving element 10. As a result, it is possible to reduce the size of the light receiving element 10 and thereby reduce the size of the laser interferometer 1. In addition, the relative parallelism of the light rays can be enhanced. Thereby, it is possible to particularly suppress a decrease in the S / N ratio of the received signal due to the interference fringes.

[0124] Further, the laser interferometer 1 according to the above embodiment includes a light intensity distribution adjuster 16 that is disposed in the optical path P4 connecting the optical splitter 4 and the light receiving element 10 and that adjusts the intensity distribution in the cross section of the incident light.

[0125] According to such a configuration, for example, in the optical path P4, the reference light L2 and the object light L3 can be collimated respectively. Thereby, the expansion of the optical path of the reference light L2 and the optical path of the object light L3 in the light receiving element 10 can be suppressed. As a result, the miniaturization of the light receiving element 10 and thereby the miniaturization of the laser interferometer 1 can be achieved. Also, the relative parallelism of the light rays can be enhanced. Thereby, the decrease in the S / N ratio of the received signal due to the interference fringes can be particularly suppressed.

[0126] Also, in the laser interferometer 1 according to the above embodiment, the light intensity distribution adjuster 16 has a function of diffusing the light transmitted through the first condenser lens 13 and focusing the light not transmitted through the first condenser lens 13.

[0127] According to such a configuration, according to the function of the light intensity distribution adjuster 16, for example, while collimating the diverging object light L2, the converging object light L3 can also be collimated. Thereby, the expansion of the optical path of the reference light L2 and the optical path of the object light L3 in the light receiving element 10 can be suppressed. As a result, the miniaturization of the light receiving element 10 and thereby the miniaturization of the laser interferometer 1 can be achieved. Also, the relative parallelism of the light rays can be enhanced. Thereby, the decrease in the S / N ratio of the received signal due to the interference fringes can be particularly suppressed.

[0128] Also, in the laser interferometer 1 according to the above embodiment, the light receiving element 10 is a differential amplification type light receiving module.

[0129] According to such a configuration, the noise included in the mixed light of the reference light L2 and the object light L3 can be canceled or reduced, and the S / N ratio of the received signal can be particularly increased.

[0130] Also, in the laser interferometer 1 according to the above embodiment, the optical splitter 4 is a polarization beam splitter.

[0131] According to such a configuration, it is easy to suppress the light quantity loss when splitting the emitted light L1 (laser light) into two. Therefore, it is possible to suppress a decrease in the S / N ratio of the received signal due to the light quantity loss.

[0132] As described above, the laser interferometer of the present invention has been described based on the illustrated embodiments. However, the laser interferometer of the present invention is not limited to the above-described embodiments, and the configuration of each part can be replaced with any configuration having the same function. Further, any other arbitrary components may be added to the laser interferometer according to the above-described embodiments.

[0133] Further, the laser interferometer of the present invention may have a configuration in which two or more of the above-described embodiments are combined.

[0134] Furthermore, the laser interferometer of the present invention is applicable not only to the displacement meter and the speed meter described above, but also to, for example, a vibration meter, an inclinometer, a distance meter (length measuring instrument), etc. In addition, as applications of the laser interferometer of the present invention, there are optical communication interference measurement techniques enabling distance measurement, 3D imaging, spectroscopy, etc., an optical fiber gyro realizing an angular velocity sensor, an angular acceleration sensor, etc., and a Fourier spectroscope equipped with a moving mirror device such as a Fourier spectroscopic analyzer and a shape measuring device.

[0135] Among these, the Fourier spectroscopic analyzer is applicable to, for example, an FT-IR (Fourier transform infrared spectroscopy) apparatus, an FT-NIR (Fourier transform near-infrared spectroscopy) apparatus, an FT-VIS (Fourier transform visible spectroscopy) apparatus, an FT-UV (Fourier transform ultraviolet spectroscopy) apparatus, an FT-THz (Fourier transform terahertz spectroscopy) apparatus, etc.

[0136] In addition, the shape measuring device is applicable to, for example, a white light interference shape measuring device, an optical coherence tomography (OCT) imaging device, etc.

[0137] Also, two or more of the laser light source, the optical modulator, and the light receiving element may be mounted on the same substrate. Thereby, miniaturization and weight reduction of the interference optical system can be easily achieved, and the ease of assembly can be enhanced.

[0138] Also, although the above embodiment has a so-called Michelson type interference optical system, the laser interferometer of the present invention is also applicable to those having other types of interference optical systems, for example, a Mach-Zehnder type interference optical system.

Explanation of Signs

[0139] 1... Laser interferometer, 2... Laser light source, 4... Optical splitter, 10... Light receiving element, 12... Optical modulator, 13... First condenser lens, 14... Object, 15... Second condenser lens, 16... Light intensity distribution adjuster, 30... Vibration element, 41... 1 / 2 wavelength plate, 42... 1 / 4 wavelength plate, 43... 1 / 4 wavelength plate, 44... 1 / 2 wavelength plate, 50... Interference optical system, 51... Sensor head unit, 52... Demodulation calculation unit, 53... Preprocessing unit, 54... Demodulation processing unit, 55... Demodulated signal output unit, 59... Main body unit, 60... Signal generation unit, 61... Oscillation circuit, 101... First PD, 102... Second PD, 103... PBS, 161... Aspherical lens, 162... Convex portion, 163... Concave portion, FC1... Focus, IF... Interference region, L1... Emitted light, L1a... First split light, L1b... Second split light, L2... Reference light, L20... Light ray, L3... Object light, L30... Light ray, P1... Optical path, P1a... Optical path, P1b... Optical path, P2... Optical path, P3... Optical path, P4... Optical path, Δx... Distance, Φlen... Effective diameter, Φco... Optical diameter

Claims

1. A laser light source that emits laser light, An optical splitter that splits the laser light into a first split light and a second split light, An optical modulator that modulates the frequency of the first split light to generate a reference light, A light receiving element that receives the object light generated by reflecting the second split light from an object and the reference light, A first condenser lens that is disposed in the optical path of the first split light or the optical path of the second split light and condenses the incident light, Comprising: When the first condenser lens is disposed in the optical path of the first split light, the light path of the reference light in the light receiving element is configured to be smaller than the light path of the object light, When the first condenser lens is disposed in the optical path of the second split light, the light path of the object light in the light receiving element is configured to be smaller than the light path of the reference light, a laser interferometer characterized by this.

2. When the focus of the first condenser lens is placed on the optical path connecting the first condenser lens and the light receiving element via the optical splitter, the light receiving element is disposed farther from the optical splitter than the focus, the laser interferometer according to claim 1.

3. The first condenser lens is disposed in the optical path of the second split light, the laser interferometer according to claim 1 or 2.

4. The first condenser lens is a collimating lens, the laser interferometer according to claim 1 or 2.

5. When the first condenser lens is disposed in the optical path of the first split light, the first split light is configured to pass through the first condenser lens and the reference light is configured not to pass through the first condenser lens, When the first condenser lens is disposed in the optical path of the second split light, the second split light is configured to pass through the first condenser lens and the object light is configured not to pass through the first condenser lens, Let the effective diameter of the first condenser lens be Φlen, Let the light path diameter of the light that is emitted from the first condenser lens and travels through the optical modulator or the object and then travels toward the first condenser lens be Φco, When the distance between the central axis of the first condenser lens and the center of the optical path of the light traveling toward the first condenser lens at the position of the first condenser lens is Δx, The laser interferometer according to claim 4 that satisfies (Φlen + Φco) / 2 < Δx.

6. The laser interferometer according to claim 1 or 2, further comprising a second condenser lens that is disposed in the optical path connecting the optical splitter and the light receiving element and condenses the incident light.

7. The laser interferometer according to claim 1 or 2, further comprising an optical intensity distribution adjuster disposed in an optical path connecting the optical splitter and the light receiving element, for adjusting an intensity distribution in a cross section of incident light.

8. The laser interferometer according to claim 7, wherein the optical intensity distribution adjuster has a function of diffusing light that has passed through the first condenser lens and focusing light that has not passed through the first condenser lens.

9. The laser interferometer according to claim 1 or 2, wherein the light receiving element is a differential amplification type light receiving module.

10. The laser interferometer according to claim 1 or 2, wherein the optical splitter is a polarization beam splitter.

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