Laser interferometer

Abstract

Provided is a laser interferometer which is easy to miniaturize, is not susceptible to decrease in measurement accuracy even if interference is applied, and has excellent usability. This laser interferometer is characterized by being provided with: a laser light source that emits laser light; the optical splitter is used for splitting the laser into first split light and second split light; a light modulator that modulates the frequency of the first split light and generates reference light; a light receiving element that receives object light and reference light generated by reflection of the second split light by the object; and a first condensing lens that is disposed on the optical path of the first split light or the optical path of the second split light and that condenses the incident light, the optical path of the reference light in the light receiving element being configured so that the optical path of the object light is smaller than the optical path of the object light in the case where the first condensing lens is disposed on the optical path of the first split light. When the first condenser lens is disposed on the optical path of the second split light, the optical path of the object light in the light receiving element is configured so as to be smaller than the optical path of the reference light.

Description

Technical Field

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

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

[0003] The laser vibrometer described in Patent Document 1 includes a vibration element that generates vibrations of a predetermined frequency. Based on its vibration frequency, this vibration element shifts the frequency of the incident laser light to generate 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. Further, by receiving, with a photodetector, the light obtained by combining the scattered laser light from the object to be measured and the reference light, a beat frequency signal is electrically extracted. Then, the vibration speed of the object to be measured is measured based on this beat frequency signal.

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

[0005] In a laser interferometer such as a laser vibrometer, the scattered laser light (object light) 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 light beam of the object light and the light beam of the reference light overlap (overlap region), and it is possible to measure the vibration speed of the object and the like.

[0006] However, in the case of forming the above-described overlap region, alignment of each part constituting the interference optical system is time-consuming and laborious. As a result, the usability of the laser interferometer is reduced. In addition, when the alignment is disrupted due to disturbances such as vibration and shock, the measurement accuracy is reduced.

[0007] On the other hand, consideration is also given to using a sensor or the like to eliminate the influence of disturbances, but in this case, there is a concern about an increase in the size and weight of the device.

[0008] Therefore, it has become a technical problem to realize a laser interferometer that suppresses an increase in size, has excellent usability, and whose measurement accuracy is not easily reduced even when disturbances are applied. Summary of the Invention

[0009] The laser interferometer according to an application example of the present invention includes:

[0010] a laser source that emits laser light;

[0011] a beam splitter that splits the laser light into a first split light and a second split light;

[0012] an optical modulator that modulates the frequency of the first split light to generate reference light;

[0013] A light-receiving element that receives object light generated by reflection of the second spectral split by an object and the reference light; and

[0014] A first condenser lens disposed on the optical path of the first spectral split or the optical path of the second spectral split, which condenses incident light,

[0015] When the first condenser lens is disposed on the optical path of the first spectral split, it is configured such that the optical path of the reference light in the light-receiving element is shorter than the optical path of the object light,

[0016] When the first condenser lens is disposed on the optical path of the second spectral split, it is configured such that the optical path of the object light in the light-receiving element is shorter than the optical path of the reference light. Description of the Drawings

[0017] Figure 1 is a functional block diagram showing a laser interferometer according to a first embodiment.

[0018] Figure 2 is showing Figure 1 a schematic structural diagram of an interference optical system included in the laser interferometer.

[0019] Figure 3 is for explaining Figure 2 the effect brought about by the first condenser lens shown.

[0020] Figure 4 is a schematic structural diagram of an interference optical system included in a laser interferometer according to a second embodiment.

[0021] Figure 5 is a schematic structural diagram of an interference optical system included in a laser interferometer according to a third embodiment.

[0022] Figure 6 is for explaining Figure 5 the effect brought about by the arrangement of the light-receiving element shown.

[0023] Figure 7 is a schematic structural diagram of an interference optical system included in a laser interferometer according to a fourth embodiment.

[0024] Figure 8 is for explaining Figure 7 the effect brought about by the second condenser lens shown.

[0025] Figure 9 is a schematic structural diagram of an interference optical system included in a laser interferometer according to a fifth embodiment.

[0026] Figure 10 is explainingFigure 9 Cross-sectional view of the action of the aspherical lens shown.

[0027] Figure 11 Fig. is a schematic structural diagram of an interference optical system included in a laser interferometer according to the sixth embodiment.

[0028] Figure 12 Fig. is a schematic structural diagram of an interference optical system included in a laser interferometer according to the seventh embodiment.

[0029] Description of reference numerals

[0030] 1: Laser interferometer; 2: Laser source; 4: Beam splitter; 10: Light receiving element; 12: Light 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; 52: Demodulation operation unit; 53: Preprocessing unit; 54: Demodulation processing unit; 55: Demodulation 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 beam split; L1b: Second beam split; 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 path length. Detailed description of the embodiments

[0031] Hereinafter, the laser interferometer of the present invention will be described in detail based on the embodiments shown in the drawings.

[0032] 1. First embodiment

[0033] Figure 1 Fig. is a functional block diagram of a laser interferometer 1 according to the first embodiment. Figure 2 Fig. shows Figure 1 schematic structural diagram of an interference optical system 50 included in the laser interferometer 1.

[0034] In Figure 1 the laser interferometer 1 shown, to Figure 2The object 14 and the optical modulator 12 shown 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 made to interfere, and the interference light is received by the light receiving element 10 to obtain a light receiving signal. Then, by heterodyne interferometry, a sample signal from the object 14 is extracted from the light receiving signal, and based on this sample signal, the displacement and speed of the object 14 are measured.

[0035] Figure 1 The laser interferometer 1 shown includes a sensor head 51 and a main body 59.

[0036] Figure 1 The sensor head 51 shown includes an interference optical system 50 and a signal generation unit 60. The sensor head 51 is easily miniaturized and lightened, and is easily movable and easy to set up. Therefore, for example, it can be easily arranged near the object 14.

[0037] The main body 59 includes a demodulation operation unit 52. The demodulation operation unit 52 demodulates a sample signal from the object 14 from the light receiving signal. Figure 1 The main body 59 shown is separated from the sensor head 51, but may also be integrated with the sensor head 51. In addition, Figure 1 At least one of the elements included in the sensor head 51 shown may also be included in the main body 59.

[0038] 1.1. Interference optical system

[0039] Figure 2 The interference optical system 50 shown is a Michelson type interference optical system. The interference optical system 50 includes a laser source 2, a beam splitter 4, a light receiving element 10, an optical modulator 12, and a first condenser lens 13.

[0040] The laser source 2 emits emitted light L1 as laser light. The emitted light L1 is incident on the beam splitter 4 through the optical path P1. The optical path refers to the path along which light travels. The beam splitter 4 divides the emitted light L1 into a first split light L1a and a second split light L1b.

[0041] The first split light L1a is incident on the optical modulator 12 through the optical path P1a. The optical modulator 12 includes a vibrating element 30, modulates the frequency of the first split light L1a, and generates reference light L2 which is laser light including a modulation signal. The modulation signal is a change in the frequency added to the first split light L1a by the optical modulator 12. The reference light L2 is incident on the beam splitter 4 through the optical path P2.

[0042] The second split light L1b is incident on the object 14 through the optical path P1b. The second split light L1b incident on the object 14 is reflected as the laser light, i.e., the object light L3, which includes the sample signal from the object 14. The sample signal is a Doppler signal accompanying the displacement of the object 14 and is a change in the frequency added to the second split light L1b. The object light L3 is incident on the beam splitter 4 through the optical path P3.

[0043] The beam splitter 4 mixes the reference light L2 and the object light L3. The mixed reference light L2 is incident on the light receiving element 10 through the optical path P4, and the mixed object light L3 is incident on the light receiving element 10 through the optical path P4. The optical paths P2 and P3 overlap each other in space, and light interference occurs in the overlapping portion. The light receiving element 10 detects the intensity of the light after the reference light L2 and the object light L3 are mixed and outputs a light receiving signal corresponding to the intensity.

[0044] In the interference optical system 50 as described above, the phase information of the object 14 is obtained by the heterodyne interference method. Specifically, two lights (the reference light L2 and the object light L3) with slightly different frequencies are made to interfere, and the phase information is extracted from the obtained interference light. Then, in the demodulation operation unit 52 described later, the displacement of the object 14 is obtained based on the phase information. In the heterodyne interference method, when extracting the phase information from the interference light, it is not easily affected by stray light or the like that becomes noise.

[0045] 1.1.1. Laser source

[0046] The laser source 2 is a laser source that emits coherent emitted light L1 (laser). The laser source 2 preferably uses a light source with a line width of below the MHz band. Specifically, gas lasers such as He-Ne lasers, semiconductor laser elements such as DFB-LD (Distributed FeedBack - Laser Diode), FBG-LD (Fiber Bragg Grating Laser Diode), VCSEL (Vertical Cavity Surface Emitting Laser), and FP-LD (Fabry-Perot Laser Diode) can be cited.

[0047] The laser source 2 is particularly preferably a semiconductor laser element. Thereby, the laser source 2 can be made particularly miniaturized. Therefore, the miniaturization of the laser interferometer 1 can be achieved.

[0048] The emitted light L1 emitted from the laser source 2 is affected by light diffraction or the like, as Figure 2The light path is expanded at a predetermined expansion angle on one side as shown and is incident on the beam splitter 4. An optical element for adjusting the expansion angle may be arranged as needed between the laser source 2 and the beam splitter 4.

[0049] 1.1.2. Beam Splitter

[0050] Figure 2 The shown beam splitter 4 is a non-polarizing beam splitter or a non-polarizing beam splitter that splits the emitted light L1 at a predetermined ratio. As an example, Figure 2 The shown beam splitter 4 reflects a part of the emitted light L1 to generate the first split light L1a, and transmits the other part of the emitted light L1 to generate the second split light L1b. Since a non-polarizing beam splitter or a non-polarizing beam splitter does not require a wavelength plate for controlling polarization, etc., it helps to reduce the number of optical elements constituting the interference optical system 50.

[0051] In addition, the beam splitter 4 has the function of mixing the incident reference light L2 and the object light L3. If the reference light L2 is incident on Figure 2 the shown beam splitter 4, a part of the light quantity is transmitted. In addition, if the object light L3 is incident on Figure 2 the shown beam splitter 4, 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.

[0052] As the type of the beam splitter 4, for example, in addition to Figure 2 the shown cubic element, plate-type elements, stacked-type elements, etc. can also be cited. Among them, from the viewpoint of suppressing the optical path difference between the reference light L2 and the object light L3, a cubic element is preferably used.

[0053] 1.1.3. Light Receiving Element

[0054] The light receiving element 10 outputs a photocurrent (light receiving signal) corresponding to the intensity of the mixed light. As the light receiving element 10, for example, a photodiode, a phototransistor, etc. can be cited. In addition, the light received by the light receiving element 10 only needs to be light containing a component from the sample and a modulation component, and is not limited to the interference light of the reference light L2 containing the above-mentioned modulation component and the object light L3 containing a component from the sample. 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).

[0055] 1.1.4. Light Modulator

[0056] Next, the light modulator 12 having the vibrating element 30 will be described.

[0057] Figure 2The illustrated optical modulator 12 has a vibrating element 30. The vibrating element 30 performs thickness shear vibration at a predetermined mechanical resonance frequency and has a diffraction grating (not shown). If the first beam splitting L1a is irradiated onto the diffraction grating, diffracted light with a frequency shift is generated, and the reference light L2 containing the modulation signal is obtained.

[0058] In addition, Figure 2 The illustrated first beam splitting L1a propagates while expanding the optical path at a predetermined divergence angle (while diverging). Therefore, the reference light L2 also diverges at the same divergence angle and is incident on the beam splitter 4.

[0059] Examples of the vibrating element 30 include a crystal oscillator, a silicon oscillator, a ceramic oscillator, a piezoelectric element, etc. Among them, the vibrating element 30 is preferably a crystal oscillator, a silicon oscillator, or a ceramic oscillator. These oscillators are different from other oscillators, such as piezoelectric elements, etc., and are oscillators that utilize the mechanical resonance phenomenon. Therefore, they have a high Q value and can easily achieve the stabilization of the natural vibration frequency.

[0060] Furthermore, according to the optical modulator 12 having the vibrating element 30, compared with an optical modulator having, for example, an acousto-optic modulator (AOM) or an electro-optic modulator (EOM), the volume and weight can be significantly reduced. Therefore, miniaturization, weight reduction, and low power consumption of the laser interferometer 1 can be achieved. In addition, even if these effects are not obtained, the above optical modulator 12 can also be replaced by an optical modulator using an AOM or an EOM.

[0061] Examples of the optical modulator 12 include the optical modulator disclosed in Japanese Patent Laid-Open No. 2022-38156. In this publication, a crystal AT oscillator can be cited as the vibrating element 30. In addition, as the vibrating element 30, an SC-cut crystal oscillator, a tuning fork type crystal oscillator, a crystal surface acoustic wave element, etc. can also be used.

[0062] A silicon oscillator is an oscillator having a single-crystalline silicon wafer and a piezoelectric film, and the single-crystalline silicon wafer is manufactured from a single-crystalline silicon substrate using MEMS technology. MEMS (Micro Electro Mechanical Systems, micro electromechanical systems) is a micro electromechanical system. Examples of the shape of the single-crystalline silicon wafer include cantilever beam shapes such as a two-legged tuning fork type and a three-legged tuning fork type, and a double-beam shape. The oscillation frequency of the silicon oscillator is, for example, about 1 kHz to several 100 MHz.

[0063] A ceramic oscillator is an oscillator having a piezoelectric ceramic sheet and electrodes, and the piezoelectric ceramic sheet is manufactured by sintering a piezoelectric ceramic. As the piezoelectric ceramic, for example, lead zirconate titanate (PZT), barium titanate (BTO), etc. can be cited. The oscillation frequency of the ceramic oscillator is, for example, about several 100 kHz to several 10 MHz.

[0064] Among them, the vibration element 30 preferably uses a crystal oscillator. Since the crystal itself is a piezoelectric material, the crystal oscillator has particularly high frequency stability.

[0065] 1.1.5. First condenser lens

[0066] Figure 2 The shown first condenser lens 13 is arranged in the overlapping part of the optical path P1b of the second spectroscope L1b and the optical path P3 of the object light L3. The first condenser lens 13 has a function of condensing the incident second spectroscope L1b and object light L3. By arranging the first condenser lens 13 in the optical path P1b, compared with the divergence angle of the incident second spectroscope L1b, the divergence angle of the emitted second spectroscope L1b can be suppressed. In Figure 2 the example, a second spectroscope L1b collimated with a divergence angle substantially zero is generated. The collimated second spectroscope L1b is irradiated onto the object 14 while maintaining the optical path. In addition, thereby, the object light L3 formed by reflecting the second spectroscope 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.

[0067] In this way, by providing the first condenser lens 13 in the optical path P1b of the second spectroscope L1b, it is easy to maintain the optical paths of the second spectroscope 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 spectroscope L1b with respect to the object 14 can be made constant. Thereby, a decrease in measurement accuracy accompanying changes in the irradiation range can be suppressed. In addition, by providing the first condenser lens 13, a significant expansion of the optical path of the object light L3 incident on the first condenser lens 13 can be suppressed. If the optical path of the object light L3 expands significantly, the amount of light of the object light L3 incident on the first condenser lens 13 decreases. 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.

[0068] The first condenser lens 13 uses any optical component having the above function. For example, an optical component called a collimating lens is used. As the collimating lens, for example, a single convex aspherical lens can be cited. In addition, the first condenser lens 13 can also be composed of a plurality of optical elements.

[0069] In addition, the object light L3 incident on the first condenser lens 13 is converged by the above-described function of the first condenser lens 13 and is incident on the spectroscope 4.

[0070] As described above, the reference light L2 is incident on the spectroscope 4 while diverging, and the object light L3 is incident on the spectroscope 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, pass through the same space, and reach the light receiving element 10. In the optical path P4, the reference light L2 and the object light L3 interfere with each other to generate mixed light including an interference signal (beat signal).

[0071] Figure 3 is a schematic diagram for explaining Figure 2 the effect brought by the first condenser lens 13 shown. Figure 3 Images showing the light intensity distributions when there is a positional shift in the optical paths P2 and P3 accompanied by interference in the case without the first condenser lens 13 and in the case with the first condenser lens 13 are shown. In this image, the horizontal axis represents the optical paths and respective positions of the reference light L2 and the object light L3, and the vertical axis represents the light intensity. Therefore, Figure 3 each curve in represents the respective light intensity distributions of the reference light L2 and the object light L3.

[0072] In the case where there is a positional shift in the optical paths P2 and P3, the position where the light reaches the light receiving element 10 also shifts. Moreover, the region (interference region IF) where the light beam of the reference light L2 overlaps and interferes with the light beam of the object light L3 becomes smaller according to the shift amount. 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 light signal.

[0073] In the case without the first condenser lens 13, like the reference light L2, the object light L3 is also incident on the spectroscope 4 while diverging. Therefore, the optical paths of the reference light L2 and the object light L3 in the light receiving element 10 become of the same degree and larger. In this case, even a slight positional shift is strongly reflected by the S / N ratio (signal-to-noise ratio) of the received light signal. Specifically, since the respective optical paths are of the same degree, the interference region IF becomes smaller according to the shift amount. As a result, the interference signal becomes smaller and the S / N ratio of the received light signal decreases. In addition, the respective light intensity distributions of the reference light L2 and the object light L3 form, for example, Figure 3 the Gaussian distribution shape shown. Thus, the influence of the positional shift is easily reflected in the interference signal, easily leading to a decrease in the S / N ratio of the received light signal. Therefore, in the case without the first condenser lens 13, a positional shift in the optical paths P2 and P3 easily leads to a decrease in the S / N ratio of the received light signal. For these reasons, the anti-interference property becomes low, and the difficulty of alignment of the interference optical system 50 also becomes high.

[0074] On the other hand, when the first condenser lens 13 is disposed 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 positional deviation, a sufficient interference region IF can be ensured. That is, since the optical path of the object light L3 is smaller than that of the reference light L2, even if a positional deviation occurs in the optical paths P2 and P3, the overlap of the light beams is maintained. As a result, a decrease in the S / N ratio of the received light signal can be suppressed. Therefore, by providing the first condenser lens 13, the anti-interference property (robustness) of the measurement accuracy can be improved. That is, a laser interferometer 1 can be realized in which the measurement accuracy is not easily reduced even when interference is applied.

[0075] In addition, 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 a positional deviation in the optical paths P2 and P3. Therefore, when aligning the interference optical system 50 before or during measurement, it is easy to obtain an interference signal, and the operation can be targeted at the intensity of the interference signal. 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.

[0076] In addition, in Figure 2 In the laser interferometer 1 shown, the above effects are achieved by disposing the first condenser lens 13. The first condenser lens 13 is small and lightweight enough, so it can contribute to the miniaturization of the laser interferometer 1. In addition, the laser interferometer 1 does not require a feedback mechanism for detecting interference and reflecting it in the measurement, so from the above viewpoints, it is also easy to achieve miniaturization and light weight.

[0077] In addition, in Figure 2 In the example of, 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, it may be configured such that the first split light L1a emitted from the first condenser lens 13 converges. In this case, it is preferable to dispose the object 14 near the focal point of the first split light L1a.

[0078] 1.2. Signal generation unit

[0079] Figure 1 The signal generation unit 60 shown outputs a drive signal input to the vibration element 30 and a reference signal input to the demodulation operation unit 52.

[0080] Figure 1The signal generation unit 60 shown 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 beam splitter L1a. Then, in the demodulation operation unit 52, the received light signal including the modulation signal is demodulated based on the reference signal. Therefore, even if interference is applied to the modulation signal and the reference signal respectively, the influence of the interference can be canceled or reduced in the demodulation operation unit 52. Thus, the laser interferometer 1 capable of performing higher-precision measurement can be realized.

[0081] As the oscillation circuit 61, for example, the oscillation circuit disclosed in Japanese Unexamined Patent Application Publication No. 2022-38156 can be cited, but it can also be an oscillation circuit having other structures.

[0082] In addition, 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.

[0083] 1.3. Demodulation operation unit

[0084] Figure 1 The demodulation operation unit 52 shown has a preprocessing unit 53, a demodulation processing unit 54, and a demodulated signal output unit 55. The functions performed by these functional units are realized by hardware including a processor, a memory, an external interface, an input unit, a display unit, etc., for example. Specifically, it is realized by the processor reading and executing a program stored in the memory. In addition, these components can communicate with each other via an external bus.

[0085] As the processor, for example, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc. can be cited. In addition, a method of realizing the above functions by using an FPGA (Field-Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), etc. can be adopted instead of the method of the processor executing software.

[0086] 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), and the like.

[0087] 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), and the like.

[0088] Examples of the input unit include various input devices such as a keyboard, a mouse, a touch panel, and a touchpad. Examples of the display unit include a liquid crystal display panel, an organic EL (Electro Luminescence) display panel, and the like.

[0089] In addition, the external interface, the input unit, and the display unit may be provided as needed or may be omitted.

[0090] The preprocessing unit 53 and the demodulation processing unit 54 can apply, for example, the preprocessing unit and the demodulation unit disclosed in Japanese Unexamined Patent Application Publication No. 2022-38156.

[0091] The preprocessing unit 53 preprocesses the received optical signal based on a reference signal. The preprocessing refers to a process of performing an operation on the received optical signal based on the reference signal to generate a signal (preprocessing completed signal) to which a known quadrature detection method can be applied.

[0092] The demodulation processing unit 54 demodulates the sample signal from the object 14 based on the reference signal according to the preprocessing completed signal output from the preprocessing unit 53, for example, by a quadrature detection method.

[0093] The demodulated signal output unit 55 performs, for example, phase connection such as unwrapping processing based on the sample signal, specifically, based on the phase information from the object 14, and calculates the displacement of the object 14. In this case, a displacement meter equipped with the laser interferometer 1 is obtained. In addition, the speed can be calculated based on the displacement, and in this case, a speed meter equipped with the laser interferometer 1 is obtained.

[0094] 2. Second Embodiment

[0095] Figure 4This is a schematic structural diagram showing the interference optical system 50 included in the laser interferometer 1 according to the second embodiment.

[0096] Hereinafter, the second embodiment will be described. In the following description, the description will focus on the points different from the first embodiment, and the description of the same matters will be omitted. In addition, Figure 4 structures identical to those of the first embodiment are denoted by the same reference numerals.

[0097] Figure 4 The interference optical system 50 shown is the same as the Figure 2 interference optical system 50 shown, except that the positions of the optical modulator 12 and the object 14 with respect to the beam splitter 4 are swapped.

[0098] That is, Figure 4 the first condenser lens 13 shown is disposed at the overlapping portion of the optical path P1a of the first split light L1a and the optical path P2 of the reference light L2. In addition, Figure 4 in this case, the light transmitted through the beam splitter 4 is taken as the first split light L1a, and the light reflected by the beam splitter 4 is taken as the second split light L1b.

[0099] Figure 4 The first split light L1a shown is converged when passing through the first condenser lens 13 and is incident on the optical modulator 12 as collimated light, for example. The reference light L2 generated by the optical modulator 12 is converged when passing through the first condenser lens 13 and is incident on the beam splitter 4. Then, it is reflected by the beam splitter 4 and mixed with the object light L3.

[0100] Figure 4 The second split light L1b shown is incident on the object 14 while diverging. The object light L3 generated by the object 14 is incident on the beam splitter 4. Then, it passes through the beam splitter 4 and is mixed with the reference light L2.

[0101] In the second embodiment as described above, the same effects as those of the first embodiment are also obtained. That is, Figure 4 the first condenser lens 13 shown is configured such that the optical path of the reference light L2 in the light receiving element 10 is shorter than the optical path of the object light L3. Thereby, it is possible to realize a laser interferometer 1 that is easily miniaturized, has a measurement accuracy that is not easily degraded even when interference is applied, and has excellent usability.

[0102] 3. Third Embodiment

[0103] Figure 5 This is a schematic structural diagram showing the interference optical system 50 included in the laser interferometer 1 according to the third embodiment.

[0104] Hereinafter, the third embodiment will be described. In the following description, the description will focus on the points different from the first embodiment, and the description of the same matters will be omitted. In addition, in Figure 5 structures identical to those of the first embodiment are denoted by the same reference numerals.

[0105] Figure 5 the interference optical system 50 shown is the same as the Figure 2 interference optical system 50 shown, except that the light receiving element 10 is arranged at a predetermined position in the optical path P4.

[0106] In Figure 5 the interference optical system 50 shown, 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 reflected by the beam splitter 4 is connected through the first condenser lens 13. Moreover, Figure 5 the light receiving element 10 shown is arranged at a position farther from the beam splitter 4 than the focal point FC1. With this structure, compared with the Figure 2 interference optical system 50 shown, 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. In addition, the "light ray" in this specification refers to the optical path of light in the unit area of the cross section.

[0107] Figure 6 is a schematic diagram for explaining the effect brought by the arrangement of the Figure 5 light receiving element 10 shown. In Figure 6 the case where the light receiving element 10 is arranged at a position closer to the focal point FC1 (closer to the beam splitter 4 side than the focal point FC1) as shown in Figure 2 , and in the case where the light receiving element 10 is arranged at a position farther from the focal point FC1 (farther from the beam splitter 4 side than the focal point FC1) as shown in Figure 5 , images are respectively formed by arrows representing the light rays L20 included in the reference light L2 and the light rays L30 included in the object light L3. In this image, 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.

[0108] When the light receiving element 10 is arranged at a position closer to the focal point FC1, the reference light L2 reaches the light receiving element 10 while diverging. In contrast, the object light L3 reaches the light receiving element 10 while converging. Therefore, the light rays L20 and the light rays L30 cross 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. Due to the influence of light and dark according to the crossing angle, the interference signal is averaged, resulting in a decrease in the S / N ratio of the received light signal.

[0109] On the other hand, when the light-receiving element 10 is disposed at a position farther from the focal point FC1, not only the reference light L2 (the light that does not pass through the first condenser lens 13), but also the object light L3 (the light converged by the first condenser lens 13) reaches the light-receiving element 10 while diverging. Therefore, the light rays L20 and L30 approach a state where they are substantially parallel to each other. Even when they cross on the light-receiving surface of the light-receiving element 10, the crossing angle can be sufficiently reduced. 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 extended. Consequently, a decrease in the S / N ratio of the received light signal caused by the interference fringes can be suppressed. In the following description, the state where the light rays L20 and L30 are close to being parallel is referred to as "high relative parallelism of the light rays".

[0110] In the third embodiment as described above, the same effects as those of the first embodiment are also obtained.

[0111] 4. Fourth Embodiment

[0112] Figure 7 FIG. is a schematic structural diagram showing an interference optical system 50 included in the laser interferometer 1 according to the fourth embodiment.

[0113] Hereinafter, the fourth embodiment will be described. However, in the following description, the description will focus on the points different from the third embodiment, and the description of the same matters will be omitted. In addition, Figure 7 the same reference numerals are assigned to the same structures as those in the third embodiment.

[0114] Figure 7 The interference optical system 50 shown is the same as that of the third embodiment except that a second condenser lens 15 is disposed on the optical path P4.

[0115] In Figure 7 the interference optical system 50 shown, 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 on the optical path P4, the reference light L2, which is divergent light, can be converged, and the divergence angle can be suppressed. In Figure 7 the example of, collimation is performed such that the divergence angle is substantially zero. On the other hand, the second condenser lens 15 also converges the object light L3 that becomes divergent light after passing through the focal point FC1. In Figure 7 the example of, collimation is performed such that the divergence angle is substantially zero.

[0116] Figure 8 is a schematic diagram for explaining Figure 7 the effects brought about by the second condenser lens 15 shown. In Figure 8 are shown respectively by arrows Figure 7An image formed by the light rays L20 included in the reference light L2 and the light rays L30 included in the object light L3 as shown.

[0117] 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 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, miniaturization of the light-receiving element 10 and thus miniaturization of the laser interferometer 1 can be achieved. In addition, in the light rays L20 and the light rays L30, the relative parallelism is improved. Thereby, a decrease in the S / N ratio of the received light signal caused by interference fringes can be particularly suppressed.

[0118] The second condenser lens 15 uses any optical component having the above function, for example, an optical component called a collimating lens. As the collimating lens, for example, a single convex aspherical lens can be cited. In addition, the second condenser lens 15 may be composed of a plurality of optical elements.

[0119] In addition, in the present embodiment, the same effects as those of the first embodiment are also obtained.

[0120] 5. Fifth Embodiment

[0121] Figure 9 FIG. is a schematic configuration diagram showing an interference optical system 50 included in the laser interferometer 1 according to the fifth embodiment.

[0122] Hereinafter, the fifth embodiment will be described. However, in the following description, the description will be centered on the points different from those of the third embodiment, and the description of the same matters will be omitted. In addition, in Figure 9 , the same reference numerals are assigned to the same structures as those of the third embodiment.

[0123] Figure 9 The interference optical system 50 shown is the same as that of the third embodiment except that a light intensity distribution adjuster 16 is disposed on the optical path P4.

[0124] In Figure 9 In the interference optical system 50 shown, a light intensity distribution adjuster 16 is disposed between the beam splitter 4 and the focal point FC1. The light intensity distribution adjuster 16 has a function of adjusting the respective light intensity distributions of the incident reference light L2 and object light L3. Figure 9 The light intensity distribution adjuster 16 shown has an aspherical lens 161. The function of the light intensity distribution adjuster 16 is determined, for example, according to the shape of the aspherical surface of the aspherical lens 161.

[0125] Figure 10 It is to illustrate Figure 9Cross-sectional view showing the function of the aspherical lens 161 shown.

[0126] Figure 10 The aspherical lens 161 shown 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 the function of converging the incident light. The concave portion 163 is a concave lens and has the function of diverging the incident light. In Figure 10 In the example, an 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, divergence is suppressed when passing through the convex portion 162. Thus, the reference light L2 can be collimated. On the other hand, Figure 10 Since the light intensity distribution adjuster 16 shown is arranged on the side closer to the beam splitter 4 than the focal point FC1, the object light L3 is incident on the concave portion 163 while converging. Therefore, the convergence of the object light L3 is suppressed when passing through the concave portion 163. Thus, the object light L3 can be collimated. Therefore, by using Figure 10 the light intensity distribution adjuster 16 shown, both the reference light L2 and the object light L3 can be collimated.

[0127] According to such a structure, an increase in 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, miniaturization of the light receiving element 10 and thus miniaturization of the laser interferometer 1 can be achieved. In addition, similar to the fourth embodiment, a decrease in the S / N ratio of the light receiving signal caused by interference fringes can be particularly suppressed.

[0128] In addition, in the present embodiment, the same effects as those of the first embodiment are also obtained.

[0129] 6. Sixth Embodiment

[0130] Figure 11 It is a schematic structural diagram showing the interference optical system 50 included in the laser interferometer 1 according to the sixth embodiment.

[0131] Hereinafter, the sixth embodiment will be described. However, in the following description, the description will be centered on the points different from the first embodiment, and the description of the same matters will be omitted. In addition, in Figure 11 the same reference numerals are assigned to the structures that are the same as those of the first embodiment.

[0132] Figure 11 The interference optical system 50 shown is the same as that of 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.

[0133] That is, in Figure 11In the interference optical system 50 shown, the posture of the optical modulator 12 with respect to the beam splitter 4 is set so that the optical path P1a is offset from the optical path P2. In addition, the posture of the object 14 with respect to the beam splitter 4 is set so that the optical path P1b is offset from the optical path P3.

[0134] In this case, the first split light L1a emitted from the beam splitter 4 enters the optical modulator 12 through the optical path P1a. Then, the reference light L2 generated by the optical modulator 12 enters the beam splitter 4 through the optical path P2 that deviates from the optical path P1a. Then, the reference light L2 passes through the beam splitter 4 and is mixed with the object light L3 in the optical path P4.

[0135] In addition, the second split light L1b emitted from the beam splitter 4 passes through the optical path P1b and the first condenser lens 13, and enters the object 14. Then, the object light L3 generated by the object 14 enters the beam splitter 4 through the optical path P3 that deviates from the optical path P1b. At this time, since the optical path P3 deviates from the optical path P1b, the object light L3 enters the beam splitter 4 without passing through the first condenser lens 13. Then, the object light L3 is reflected by the beam splitter 4 and is mixed with the reference light L2 in the optical path P4.

[0136] According to such a structure, the object light L3, which is collimated by the first condenser lens 13 for example, is not converged by the first condenser lens 13 and can reach the light receiving element 10. Therefore, 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 improved in the present embodiment. 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 extended, and the reduction of the S / N ratio of the received light signal caused by the interference fringes can be suppressed.

[0137] In addition, from the viewpoint 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 at the position of the first condenser lens 13 (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 and passes through the object 14 and then heads towards the first condenser lens 13) preferably satisfies the following formula.

[0138] (Φlen + Φco) / 2 < Δx

[0139] In the above formula, Φlen is the effective diameter of the first condenser lens 13, and Φco is the optical path of the object light L3 (the light heading towards the first condenser lens 13). By the distance Δx satisfying the above formula, the object light L3 can be suppressed from entering the first condenser lens 13. As a result, the accidental convergence of the object light L3 can be suppressed.

[0140] In addition, in the present embodiment, the same effects as those of the first embodiment are also obtained, that is, the effects that even when interference is applied, the measurement accuracy is not easily reduced and alignment is easy. As a result, a laser interferometer 1 with high anti-interference performance and excellent usability is obtained.

[0141] In addition, in the present embodiment, by tilting the optical modulator 12 and the light receiving element 10 with respect to the beam splitter 4, non-coaxialization of the optical path as described above is achieved. However, the means for achieving non-coaxialization of the optical path is not limited to this. For example, non-coaxialization of the optical path can also be achieved by adding a beam splitter and a mirror (not shown) without tilting the optical modulator 12 and the light receiving element 10.

[0142] In addition, in the present embodiment, the first condenser lens 13 is disposed on the optical path P1b. However, the first condenser lens 13 can also be disposed on the optical path P1a. In this case, the first split light L1a emitted from the beam splitter 4 passes through the optical path P1a and the first condenser lens 13 and is incident on the optical modulator 12. The reference light L2 is incident on the beam splitter 4 without passing through the first condenser lens 13. In the mixed light passing through the optical path P4, the positions of the reference light L2 and the object light L3 are Figure 11 opposite, but the same effects as those of the present embodiment are obtained.

[0143] 7. Seventh Embodiment

[0144] Figure 12 FIG. is a schematic structural diagram of an interference optical system 50 included in the laser interferometer 1 according to the seventh embodiment.

[0145] Hereinafter, the seventh embodiment will be described. However, in the following description, the description will focus on the differences from the first embodiment, and the description of the same matters will be omitted. In addition, Figure 12 structures identical to those of the first embodiment are denoted by the same reference numerals.

[0146] Figure 12 The interference optical system 50 shown is the same as the interference optical system 50 shown except that the beam splitter 4 is a polarization beam splitter and the light receiving element 10 is composed of a differential amplification type light receiving module. Figure 2 The interference optical system 50 shown.

[0147] Figure 12 The beam splitter 4 shown is a polarization beam splitter and has a function of reflecting S-polarized light and transmitting P-polarized light. Specifically, Figure 12 the beam splitter 4 shown divides the emitted light L1 into a first split light L1a as S-polarized light and a second split light L1b as P-polarized light. By this function, in Figure 12In the optical splitter 4 shown, it is easy to suppress the optical power loss when splitting the emitted light L1 into two. Thus, it is possible to suppress the reduction in the S / N ratio of the received light signal accompanying the optical power loss.

[0148] Between Figure 12 On the optical path P1 between the laser source 2 and the optical splitter 4 shown, a half-wave plate 41 is disposed. The emitted light L1 emitted from the laser source 2 passes through the half-wave plate 41, and thus is converted into linearly polarized light with an intensity ratio of S-polarized light to P-polarized light, for example, 50:50.

[0149] Between Figure 12 On the optical path P1a between the optical splitter 4 and the optical modulator 12 shown, a quarter-wave plate 42 is disposed. The S-polarized light, i.e., the first split light L1a, 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.

[0150] Between Figure 12 On the optical path P2 between the optical modulator 12 and the optical splitter 4 shown, a quarter-wave plate 42 is disposed. The reference light L2 passes through the optical path P2 and 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 in the optical path P4.

[0151] Figure 12 On the optical path P1b between the optical splitter 4 and the object 14 shown, a first condenser lens 13 and a quarter-wave plate 43 are disposed. The P-polarized light, i.e., the second split light L1b, emitted from the optical splitter 4 is converged 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.

[0152] Between Figure 12 On the optical path P3 between the object 14 and the optical splitter 4 shown, a quarter-wave plate 43 and a first condenser lens 13 are disposed. The object light L3 passes through the optical path P3 and is converted into S-polarized light by the quarter-wave plate 43. The object light L3 converted into S-polarized light is converged 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 in the optical path P4.

[0153] A half-wave plate 44 is disposed on the optical path P4. When the mixed light passes through the half-wave plate 44, the polarization states are made consistent. Thus, interference between the reference light L2 and the object light L3 is generated, and the mixed light containing the interference signal is incident on the light receiving element 10.

[0154] As described above, Figure 12 The light receiving element 10 shown is composed of a differential amplification type light receiving module. Figure 12The light receiving element 10 shown has 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. In addition, the PBS 103 preferably uses a polarization beam splitter. The mixed light incident on the light receiving element 10 is split by the PBS 103 into S-polarized light and P-polarized light. 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 improved. In addition, in the light receiving element 10, each optical element may not be modularized. Further, from the viewpoint of making the optical path difference zero in 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 cubic element.

[0155] In the seventh embodiment as described above, the same effects as those of the first embodiment are also obtained.

[0156] 8. Effects achieved by the described embodiments

[0157] As described above, the laser interferometer 1 according to the described embodiment includes a laser source 2, a beam splitter 4, an optical modulator 12, a light receiving element 10, and a first condenser lens 13. The laser source 2 emits emitted light L1 (laser). The beam 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 the 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. Moreover, when the first condenser lens 13 is disposed on the optical path P1a of the first split light L1a, it 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. In addition, when the first condenser lens 13 is disposed on the optical path P1b of the second split light L1b, it is configured such that the optical path of the object light L3 in the light receiving element 10 is smaller than the optical path of the reference light L2.

[0158] According to such a structure, the optical path of either the reference light L2 or the object light L3 becomes relatively smaller, it is easy to ensure the region where the two coincide and interfere, and even if disturbances such as vibration and shock are applied, it is easy to maintain the interference state. Therefore, the S / N ratio of the received signal is not easily reduced. In addition, the first condenser lens 13 is sufficiently small and lightweight, and there is no need for a feedback mechanism or the like that detects disturbances and reflects them in the measurement. Therefore, according to the structure as described above, it is possible to realize a laser interferometer 1 that is easily miniaturized, has a measurement accuracy that is not easily reduced even when disturbances are applied, and has excellent usability.

[0159] In addition, 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 beam splitter 4, the light receiving element 10 is arranged at a position farther from the beam splitter 4 than the focal point FC1.

[0160] According to such a structure, not only the reference light L2 (the light that does not pass through the first condenser lens 13), but also the object light L3 (the light converged by the first condenser lens 13) reaches the light receiving element 10 while diverging. Thereby, the relative parallelism of the light rays becomes higher, and a decrease in the S / N ratio of the light receiving signal caused by interference fringes can be suppressed.

[0161] In addition, in the laser interferometer 1 according to the embodiment, the first condenser lens 13 is arranged on the optical path P1b of the second beam splitter L1b.

[0162] According to such a structure, it is easy to maintain the optical paths of the second beam splitter 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 beam splitter L1b with respect to the object 14 can be made constant. Thereby, a decrease in the measurement accuracy accompanying the change 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. If the optical path of the object light L3 expands significantly, the amount of light of the object light L3 incident on the first condenser lens 13 decreases. 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 receiving signal can be suppressed.

[0163] In addition, in the laser interferometer 1 according to the embodiment, the first condenser lens 13 is a collimating lens.

[0164] According to such a structure, since it is easy to maintain the optical paths of the light irradiated on the optical modulator 12 and the object 14, 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 receiving signal can be suppressed.

[0165] In addition, in the laser interferometer 1 according to the embodiment, when the first condenser lens 13 is disposed on the optical path P1a of the first beam splitter L1a, it is configured such that the first beam splitter L1a transmits through the first condenser lens 13 and the reference light L2 does not transmit through the first condenser lens 13. Further, when the first condenser lens 13 is disposed on the optical path P1b of the second beam splitter L1b, it is configured such that the second beam splitter L1b transmits through the first condenser lens 13 and the object light L3 does not transmit through the first condenser lens 13. Moreover, when the effective diameter of the first condenser lens 13 is Φlen, the optical path of the light that is emitted from the first condenser lens 13 and then travels through the optical modulator 12 or the object 14 and then towards the first condenser lens 13 is Φco, and the distance between the central axis of the first condenser lens 13 at the position of the first condenser lens 13 and the center of the optical path of the light towards the first condenser lens 13 is Δx, it satisfies (Φlen + Φco) / 2 < Δx.

[0166] According to such a configuration, it is possible to suppress the light that travels through the optical modulator 12 or the object 14 and then towards the first condenser lens 13 from entering the first condenser lens 13. Thereby, it is possible to suppress the accidental convergence of this light.

[0167] In addition, the laser interferometer 1 according to the embodiment includes a second condenser lens 15 that is disposed on the optical path P4 connecting the beam splitter 4 and the light receiving element 10 and condenses the incident light.

[0168] According to such a configuration, for example, in the optical path P4, it is possible to collimate the reference light L2 and the object light L3, respectively. Thereby, it is possible to suppress 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. As a result, it is possible to miniaturize the light receiving element 10 and thereby miniaturize the laser interferometer 1. In addition, the relative parallelism of the light rays is improved. Thereby, it is possible to particularly suppress the reduction in the S / N ratio of the received signal caused by the interference fringes.

[0169] In addition, the laser interferometer 1 according to the embodiment includes a light intensity distribution adjuster 16 that is disposed on the optical path P4 connecting the beam splitter 4 and the light receiving element 10 and adjusts the intensity distribution on the cross section of the incident light.

[0170] According to such a configuration, for example, in the optical path P4, it is possible to collimate the reference light L2 and the object light L3, respectively. Thereby, it is possible to suppress 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. As a result, it is possible to miniaturize the light receiving element 10 and thereby miniaturize the laser interferometer 1. In addition, the relative parallelism of the light rays is improved. Thereby, it is possible to particularly suppress the reduction in the S / N ratio of the received signal caused by the interference fringes.

[0171] In addition, in the laser interferometer 1 according to the embodiment, the light intensity distribution adjuster 16 has a function of diffusing the light that has passed through the first condenser lens 13 and converging the light that has not passed through the first condenser lens 13.

[0172] According to such a structure, based on the functions of the light intensity distribution adjuster 16, for example, the divergent object light L2 can be collimated, and on the other hand, the converging object light L3 can also be collimated. As a result, 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, miniaturization of the light receiving element 10 and thus miniaturization of the laser interferometer 1 can be achieved. In addition, the relative parallelism of the light rays is improved. As a result, a decrease in the S / N ratio of the received light signal caused by interference fringes can be particularly suppressed.

[0173] In addition, in the laser interferometer 1 according to the embodiment, the light receiving element 10 is a differential amplification type light receiving module.

[0174] According to such a structure, 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 light signal can be particularly improved.

[0175] In addition, in the laser interferometer 1 according to the embodiment, the beam splitter 4 is a polarization beam splitter.

[0176] According to such a structure, it is easy to suppress the light quantity loss when the emitted light L1 (laser) is split into two. Therefore, a decrease in the S / N ratio of the received light signal due to the light quantity loss can be suppressed.

[0177] As described above, the laser interferometer of the present invention has been described based on the illustrated embodiment, but the laser interferometer of the present invention is not limited to the embodiment, and the structure of each part can be replaced with any structure having the same function. In addition, any other constituent elements can be added to the laser interferometer according to the embodiment.

[0178] In addition, the laser interferometer of the present invention may also have a structure combining two or more of the above-described embodiments.

[0179] Furthermore, in addition to the displacement meter and the speed meter described above, the laser interferometer of the present invention can be applied to, for example, a vibrometer, an inclinometer, a distance meter (length measuring instrument), etc. In addition, as applications of the laser interferometer of the present invention, there can be cited optical comb interferometry techniques capable of distance measurement, 3D imaging, spectroscopy, etc., fiber optic gyroscopes for realizing angular velocity sensors, angular acceleration sensors, etc., Fourier spectroscopic analysis devices, shape measurement devices, etc., such as Fourier spectrometers equipped with a moving mirror device.

[0180] Among them, the Fourier spectroscopic analysis device can be applied to, for example, FT-IR (Fourier transform infrared spectroscopic analysis) devices, FT-NIR (Fourier transform near-infrared spectroscopic analysis) devices, FT-VIS (Fourier transform visible spectroscopic analysis) devices, FT-UV (Fourier transform ultraviolet spectroscopic analysis) devices, FT-THz (Fourier transform terahertz spectroscopic analysis) devices, and the like.

[0181] In addition, the shape measurement device can be applied to, for example, a white light interference shape measurement device, an optical coherence tomography (OCT) imaging device, and the like.

[0182] In addition, two or more of the laser source, the optical modulator, and the light receiving element can also 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 improved.

[0183] In addition, the above-described embodiment has a so-called Michelson-type interference optical system, but the laser interferometer of the present invention can also be applied to an interference optical system having other types, such as a Mach-Zehnder type interference optical system.

Claims

1. A laser interferometer, characterized in that, Comprising: A laser source that emits laser light; A beam splitter that splits the laser light into a first split beam and a second split beam; An optical modulator that modulates the frequency of the first split beam to generate a reference light; A light receiving element that receives the object light generated by reflection of the second split beam by an object and the reference light; And A first condenser lens disposed on the optical path of the first split beam or the optical path of the second split beam to condense the incident light, When the first condenser lens is disposed on the optical path of the first split beam, it is configured such that the optical path of the reference light in the light receiving element is smaller than the optical path of the object light, When the first condenser lens is disposed on the optical path of the second split beam, it is configured such that the optical path of the object light in the light receiving element is smaller than the optical path of the reference light.

2. The laser interferometer according to claim 1, wherein 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 beam splitter, the light receiving element is disposed at a position farther from the beam splitter than the focus.

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

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

5. The laser interferometer according to claim 4, wherein When the first condenser lens is disposed on the optical path of the first split beam, it is configured such that the first split beam passes through the first condenser lens and the reference light does not pass through the first condenser lens, When the first condenser lens is disposed on the optical path of the second split beam, it is configured such that the second split beam passes through the first condenser lens and the object light does not pass through the first condenser lens, When the effective diameter of the first condenser lens is set to Φlen, The optical path of the light that exits the first condenser lens and then passes through the optical modulator or the object and then heads towards the first condenser lens is set to Φco, When the distance between the central axis of the first condenser lens at the position of the first condenser lens and the center of the optical path of the light heading towards the first condenser lens is set to Δx, It satisfies (Φlen + Φco) / 2 < Δx.

6. The laser interferometer according to claim 1 or 2, wherein The laser interferometer includes a second condenser lens, and the second condenser lens is disposed on the optical path connecting the beam splitter and the light receiving element to condense the incident light.

7. The laser interferometer according to claim 1 or 2, wherein The laser interferometer includes a light intensity distribution adjuster, and the light intensity distribution adjuster is disposed on the optical path connecting the beam splitter and the light receiving element to adjust the intensity distribution on the cross section of the incident light.

8. The laser interferometer according to claim 7, wherein The light intensity distribution adjuster has a function of diffusing the light that has passed through the first condenser lens and converging the 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 beam splitter is a polarization beam splitter.

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