Laser interferometer and method for adjusting the optical axis of a laser interferometer

Abstract

To provide a laser interferometer that can efficiently adjust the optical axis to suppress the generation of interference fringes and suppress a decrease in the signal-to-noise ratio of the received light signal, and a method for adjusting the optical axis of a laser interferometer that can efficiently adjust the optical axis of the laser interferometer. [Solution] A laser interferometer comprising: a laser light source; a first optical splitter that splits laser light into a first light and a second light; an optical modulator that generates a reference light; a first photodetector that receives the reference light and object light and outputs a received signal; a second optical splitter that is placed on the optical path connecting the laser light source and the first optical splitter and guides the reflected light of the reference light and the reflected light of the object light to a second optical path different from the first optical path toward the laser light source; a second photodetector that acquires the reception position for the reflected light; a reception position display unit that displays the reception position; an AC level acquisition unit that acquires the AC level due to the interference between the reference light and object light included in the received signal; and an AC level display unit that displays the AC level.

Description

Technical Field

[0001] The present invention relates to a laser interferometer and a method for adjusting the optical axis of 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, a laser beam is irradiated onto the object to be measured, and the vibration speed is measured based on the scattered laser beam 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 beam based on its vibration frequency and generates a reflected laser beam having a frequency different from that of the incident laser beam. In the laser vibrometer, this reflected laser beam is used as the reference light. Then, the light in which the scattered laser beam derived from the object to be measured and the reference light are combined is received by a photodetector, and the beat signal is electrically extracted, and the vibration speed of the object to be measured is measured from this beat signal.

[0004] However, in a laser light source, the return light may enter, which may cause the laser oscillation to become unstable. The return light refers to the light that unintentionally returns toward the laser light source when the laser beam emitted from the laser light source is reflected by an optical component. When the laser oscillation becomes unstable, the quality of the laser beam deteriorates. As a result, in the laser vibrometer, the S / N ratio (signal-to-noise ratio) decreases and the phase of the laser beam becomes discontinuous. Consequently, the measurement accuracy of the vibration speed of the object decreases.

[0005] Non-coaxial optical systems are known as a technique for suppressing reflected light. A non-coaxial optical system is an optical system in which the reflective surface of an optical component is tilted so that the light incident on the optical component (incident light) and the light reflected by this light (reflected light) propagate along different axes. By tilting the reflective surface, even if some of the reflected light returns towards the laser light source, it will return to a position offset from the laser light source. Therefore, it is possible to suppress the entry of reflected light into the light emission part of the laser light source.

[0006] Applying the above-described non-coaxial optical system to a laser vibrometer is expected to suppress the destabilization of laser oscillation caused by reflected light. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2007-285898 [Overview of the project] [Problems that the invention aims to solve]

[0008] When a non-coaxial optical system is applied to the laser vibrometer described in Patent Document 1, scattered laser light originating from the object under test (object light) and the reference light are combined and received by a photodetector. In this case, if the optical axis of the object light and the optical axis of the reference light are not parallel, interference occurs in the region where the two beams overlap (overlap region). When the optical axes of the beams are parallel, there is no difference in the optical path length at each point in the overlap region, so there is no difference in the interference state. However, when the optical axes of the beams are not parallel, there is a difference in the optical path length at each point in the overlap region, and a difference in the interference state occurs. Therefore, when observed on an observation plane that intersects each optical axis, light and dark fringes (interference fringes) will be observed.

[0009] Since the photodetector is placed on this observation surface, the intensity of the interference fringes is averaged out for detection. As a result, the signal-to-noise ratio of the received signal becomes low.

[0010] Therefore, the challenge is to adjust the optical axis to suppress the generation of interference fringes in the overlapping region of the non-coaxial optical system, thereby suppressing the decrease in the signal-to-noise ratio of the received light signal. [Means for solving the problem]

[0011] A laser interferometer according to an application example of the present invention is, A laser light source that emits laser light, A first light splitter that splits the aforementioned laser light into a first light and a second light, A light modulator that modulates the frequency of the first light and generates a reference light, A first light-receiving element that receives object light generated when the reference light and the second light are irradiated onto an object, and outputs a light-receiving signal based on the light-receiving intensity, A second optical splitter is positioned on the optical path connecting the laser light source and the first optical splitter, and guides the reflected light of the reference light and the reflected light of the object light generated in the first optical splitter to a second optical path different from the first optical path toward the laser light source. A second light-receiving element is arranged in the second optical path and acquires the respective light-receiving positions for the reflected light of the reference light and the reflected light of the object light, A light-receiving position display unit that displays the acquired light-receiving position, An AC level acquisition unit that acquires the AC level due to the interference between the reference light and the object light included in the received light signal, An AC level display unit that displays the acquired AC level, It is equipped with.

[0012] The optical axis adjustment method for a laser interferometer according to an application example of the present invention is: A method for adjusting the optical axis of a laser interferometer, The aforementioned laser interferometer is A laser light source that emits laser light, A first light splitter that splits the aforementioned laser light into a first light and a second light, A light modulator that modulates the frequency of the first light and generates a reference light, A first light receiving element that receives object light generated by irradiating the reference light and the second light onto an object and outputs a light reception signal based on the light reception intensity; A second optical splitter that is disposed on an optical path connecting the laser light source and the first optical splitter and guides return light of the reference light and return light of the object light generated by the first optical splitter to a second optical path different from the first optical path leading to the laser light source; A second light receiving element that is disposed on the second optical path and acquires respective light reception positions of the return light of the reference light and the return light of the object light; and Moving the light reception position of the return light of the object light to a starting point by performing a change operation for changing a relative relationship between the laser interferometer and the object based on the light reception position acquired by the second light receiving element; Acquiring an AC level due to interference between the reference light and the object light included in the light reception signal while performing a scan operation for continuously changing the relative relationship from the starting point; Ending the scan operation when the acquired AC level satisfies a predetermined condition; and having.

Brief Description of Drawings

[0013] [Figure 1] It is a block diagram showing a laser interferometer according to an embodiment. [Figure 2] It is a schematic configuration diagram showing an interference optical system included in the laser interferometer of FIG. 1. [Figure 3] It is an example of an external view of a sensor head portion shown in FIG. 1. [Figure 4] It is a flowchart showing a configuration of an optical axis adjustment method of a laser interferometer according to an embodiment. [Figure 5] It is a diagram showing an example of each light reception position of return light and a warning range displayed on a light reception position display portion. [Figure 6] It is a diagram showing an example of teaching in an operation teaching portion to change a posture of a figure simulating a housing. [Figure 7]Figure 5 shows a table summarizing the relationship between the three positions through which the reflected light, displayed on the light receiving position indicator, passes during the scanning operation, and the corresponding AC level, incident direction of the reference light and object light, interference image, positional shift, angular shift, and presence or absence of interference fringes at each position. [Figure 8] This is a schematic diagram showing the interference optical system of the laser interferometer according to the first modified example. [Figure 9] This is a schematic diagram showing the interference optical system of the laser interferometer according to the second modified example. [Modes for carrying out the invention]

[0014] The laser interferometer and the method for adjusting the optical axis of the laser interferometer according to the present invention will be described in detail below based on the embodiments shown in the attached drawings.

[0015] Figure 1 is a block diagram showing a laser interferometer 1 according to an embodiment. Figure 2 is a schematic configuration diagram showing the interference optical system 50 included in the laser interferometer 1 of Figure 1.

[0016] The laser interferometer 1 shown in Figure 1 irradiates the object 14 and the optical modulator 12 shown in Figure 2 with laser light. The laser light emitted from the object 14 and the laser light emitted from the optical modulator 12 are then interfered with, and the interference light is received by the first photodetector 10. Then, information originating from the object 14 is extracted using optical heterodyne interferometry, and the displacement and velocity of the object 14 are measured based on that information.

[0017] The laser interferometer 1 shown in Figure 1 comprises a sensor head 71 and a main body 72. The sensor head 71 is easy to miniaturize and lighten, and is easy to make portable and install, so it can be placed, for example, near the object 14 shown in Figure 2, which is the object to be measured by the laser interferometer 1.

[0018] The main unit 72 includes a demodulation calculation unit 52, a light receiving position display unit 56, an AC level acquisition unit 57, an AC level display unit 58, and an operation teaching unit 59. The main unit 72 may be integrated with the sensor head unit 71, but it can be positioned separately from the sensor head unit 71, and may be a stationary type that can be housed in a rack, for example, or a portable type that can be carried around. Furthermore, at least one of the above-mentioned functional units of the main unit 72 may be located on the sensor head unit 71.

[0019] 1. Laser interferometer The sensor head unit 71 shown in Figure 1 comprises an interference optical system 50 and a signal generation unit 60, and a housing 70 that houses them.

[0020] 1.1 Interferometric Optics The interference optical system 50 shown in Figure 2 is a Michelson-type interference optical system. The interference optical system 50 comprises a laser light source 2, a collimating lens 85, a shielding element 86, a first optical splitter 41, a half-wave plate 81, a quarter-wave plate 82, a quarter-wave plate 83, an analyzer 84, a first photodetector 10, an optical modulator 12, a second optical splitter 42, and a second photodetector 32.

[0021] The optical path connecting the laser light source 2 and the second optical splitter 42 is defined as optical path 17 (first optical path). The optical path connecting the second optical splitter 42 and the first optical splitter 41 is defined as optical path 18. The optical path connecting the first optical splitter 41 and the optical modulator 12 is defined as optical path 20. The optical path connecting the first optical splitter 41 and the object 14 is defined as optical path 22. The optical path connecting the first optical splitter 41 and the first photodetector 10 is defined as optical path 24. In this specification, "optical path" refers to the path through which light travels, set between optical components. Furthermore, "optical axis," as described later, refers to the central axis of the traveling beam.

[0022] The laser light source 2 emits laser light L1. The laser light L1 is incident on the first optical splitter 41 via a collimating lens 85 and a shielding element 86 provided on the optical path 17, and a second optical splitter 42 and a half-wave plate 81 provided on the optical path 18.

[0023] The first optical splitter 41 is located on the optical path 18 and splits the laser light L1 into two beams: a first beam L1a and a second beam L1b.

[0024] The first light, L1a, is irradiated onto the optical modulator 12 via a quarter-wave plate 83 located on the optical path 20. The optical modulator 12 modulates the frequency of the first light, L1a. Therefore, the first light, L1a, undergoes interactions such as reflection in the optical modulator 12 to become the reference light, L2. The reference light, L2, is then incident on the first optical divider 41 via the quarter-wave plate 83.

[0025] The second light, L1b, is irradiated onto the object 14 via a quarter-wave plate 82 located on the optical path 22. The object 14, which undergoes displacement such as vibration, shifts the frequency of the second light, L1b. Therefore, the second light, L1b, undergoes interactions such as reflection at the object 14 and becomes object light, L3. The object light, L3, is then incident on the first light divider 41 via the quarter-wave plate 82.

[0026] The first optical splitter 41 mixes the reference light L2 and the object light L3. The mixed reference light L2 and object light L3 are then incident on the first photodetector 10 via an analyzer 84 located on the optical path 24.

[0027] The first light-receiving element 10 receives the reference light L2 and the object light L3, and outputs a light-receiving signal based on the light-receiving intensity.

[0028] In the interference optical system 50 described above, the phase information of the object 14 is obtained by optical heterodyne interferometry. Specifically, two lights with slightly different frequencies (reference light L2 and object light L3) are interfered with, and phase information is extracted from the resulting interference light. Then, the displacement of the object 14 is determined from the phase information in the demodulation calculation unit 52, which will be described later. Optical heterodyne interferometry is less susceptible to the influence of disturbances, especially stray light which acts as noise, when extracting phase information from interference light, thus providing high robustness.

[0029] The reference light L2 generated by the optical modulator 12 and incident on the first optical divider 41 passes through the first optical divider 41 and is received by the first photodetector 10, but a portion is reflected. The reflected reference light L2 may travel back to the laser light source 2 as return light L4 along the optical paths 18 and 17.

[0030] Similarly, the object light L3 incident on the first optical splitter 41 is reflected by the first optical splitter 41 and received by the first photodetector 10, but some of it is transmitted. The transmitted object light L3 may travel back to the laser light source 2 as reflected light L5 along the optical paths 18 and 17.

[0031] When such reflected light L4 and L5 is incident on the laser light source 2, the laser oscillation in the laser light source 2 becomes unstable, and the quality of the laser light L1 deteriorates.

[0032] Therefore, in the interference optical system 50 shown in Figure 2, a non-coaxial optical system is employed. In the interference optical system 50 employing a non-coaxial optical system, the optical path 20 followed by the first light L1a and the optical path 20 followed by the reference light L2 are offset from each other. Similarly, the optical path 22 followed by the second light L1b and the optical path 22 followed by the object light L3 are also offset from each other. With such a non-coaxial optical system, even if a portion of the reference light L2 is directed towards the laser light source 2 as a return beam L4, it will reach a position offset from the emission point of the laser light L1. Similarly, if a portion of the object light L3 is directed towards the laser light source 2 as a return beam L5, it will also reach a position offset from the emission point of the laser light L1. As a result, the return beams L4 and L5 are less likely to affect the laser oscillation of the laser light source 2. The emission point refers to the surface from which the laser light L1 is emitted in the laser light source 2.

[0033] In order to obtain the above-mentioned functions and effects in the interference optical system 50, precise optical axis adjustment is necessary. Specifically, the reference light L2 generated by the optical modulator 12 must travel to the first optical splitter 41 not along the same optical path 20 as the first light L1a, but along an optical path 20 that is slightly tilted relative to it. For this to be possible, the input and output surfaces of the optical modulator 12 must be tilted relative to the input and output surfaces of the first optical splitter 41. However, it is difficult to perform the operation of tilting the input and output surfaces of the optical modulator 12 retrospectively (after the interference optical system 50 has been housed in the housing 70).

[0034] On the other hand, the object light L3 generated by the object 14 needs to follow a slightly tilted optical path 22, rather than the same optical path 22 as the second light L1b, to reach the first light splitter 41. For this to be possible, it is necessary to tilt the light input / output surface of the object 14 with respect to the interference optical system 50, or to tilt the interference optical system 50 with respect to the object 14. Hereinafter, such an operation will also be referred to as "an operation that changes the relative relationship between the housing 70 and the object 14." The relative relationship refers to the relative relationship between the attitude and position of the housing 70 and the attitude and position of the object 14. Since such an operation can be performed retrospectively, the user of the laser interferometer 1 performs the above operation to adjust the optical axis before measuring the position of the object 14, etc.

[0035] In interference optical systems 50 employing non-coaxial optical systems, the optical axis must be adjusted to satisfy the following three elements (a), (b), and (c).

[0036] (a) The reflected light L4 and L5 shall not be incident on the emission part of the laser light source 2. (b) The beam of reference light L2 and the beam of object light L3 overlap on the light-receiving surface of the first photodetector 10. (c) The optical axis of the reference light L2 and the optical axis of the object light L3 are parallel on the light-receiving surface of the first light-receiving element 10.

[0037] By adjusting the optical axis to satisfy the three elements (a), (b), and (c) described above, it is possible to suppress the generation of interference fringes in the interference between the object light L3 and the reference light L2, while also suppressing a decrease in the signal-to-noise ratio (S / N ratio) of the received signal. This makes it possible to realize a laser interferometer 1 that can measure the displacement of the object 14 with high precision.

[0038] However, for the user, adjusting the optical axis to satisfy the three elements mentioned above is quite difficult.

[0039] Therefore, in the laser interferometer 1 according to this embodiment, the reflected light L4 and L5 generated in the first optical splitter 41, that is, the reflected light L4 and L5 generated in a direction different from the reference light L2 and object light L3 directed to the optical path 24 by the first photodetector 10 (in a direction along the optical path 18), is observed by the second photodetector 32. By using this observation result, the difficulty of optical axis adjustment can be reduced. The reflected light L4 and L5 shown in Figure 2 will be described below.

[0040] The interference optical system 50 shown in Figure 2 is equipped with a second optical divider 42 and a second photodetector 32.

[0041] The second optical splitter 42 is located on optical paths 17 and 18. Therefore, when the reflected light L4 and L5 travel back to the laser light source 2 along optical paths 18 and 17, they are incident on the second optical splitter 42 before reaching the laser light source 2. The second optical splitter 42 splits the incident reflected light L4 and L5. A portion of the split reflected light L4 and L5 is directed towards the laser light source 2, and the other portion is directed towards the second photodetector 32. The optical path connecting the second optical splitter 42 and the second photodetector 32 is called optical path 19 (second optical path).

[0042] The second light-receiving element 32, located on the optical path 19, receives the divided reflected light L4 and L5 and obtains the respective light-receiving positions.

[0043] Furthermore, the laser interferometer 1 shown in Figures 1 and 2 includes a light receiving position display unit 56, an AC level acquisition unit 57, and an AC level display unit 58.

[0044] The light-receiving position display unit 56 displays the light-receiving position on the second light-receiving element 32 of the reflected light L4 and L5 acquired by the second light-receiving element 32.

[0045] The AC level acquisition unit 57 acquires the AC level due to the interference between object light L3 and reference light L2 included in the received light signal. The AC level display unit 58 displays the acquired AC level.

[0046] With the above configuration, when a user of the laser interferometer 1 performs optical axis adjustment by changing the relative relationship between the housing 70 and the object 14, the user can be provided with information to satisfy the three elements (a), (b), and (c) described above. Specifically, by making the user aware of the display content of the light receiving position display unit 56, optical axis adjustment can be assisted mainly to satisfy elements (a) and (b). In addition, by making the user aware of the display content of the AC level display unit 58, optical axis adjustment can be assisted mainly to satisfy elements (b) and (c).

[0047] Furthermore, the operation teaching unit 59 teaches the user of the laser interferometer 1 the above-mentioned modification operation based on the acquired light receiving position. This makes it easier for the user to understand the direction and amount of change when changing at least one of the orientation and position of the housing 70 and the orientation and position of the object 14. As a result, the user can easily and quickly complete the optical axis adjustment. Note that the housing 70 and the operation teaching unit 59 may be provided as needed and may be omitted. If the housing 70 is omitted, the relative relationship between the interference optical system 50 (laser interferometer 1) and the object 14 may be changed.

[0048] The following provides a further explanation of each part of the interference optical system 50. 1.1.1. Laser light source Laser light source 2 is a laser light source that emits coherent laser light L1. Preferably, laser light source 2 uses a light source with a linewidth of MHz or less. Specifically, examples include 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 Lasers), and semiconductor laser elements such as FP-LDs (Fabry-Perot Laser Diodes).

[0049] The laser light source 2 is preferably a semiconductor laser element. This makes it possible to miniaturize the laser light source 2. As a result, the sensor head unit 71, which houses the interference optical system 50, can be made smaller and lighter, thereby improving the installation flexibility, portability, and operability of the sensor head unit 71.

[0050] The laser light L1 emitted from the laser light source 2 sequentially passes through the collimating lens 85 and shielding element 86 provided on the optical path 17, and the second optical splitter 42 and half-wave plate 81 provided on the optical path 18, before being incident on the first optical splitter 41.

[0051] 1.1.2. Collimating Lenses The collimating lens 85 parallelizes the laser beam L1 emitted from the laser light source 2. An example of a collimating lens 85 is an aspherical lens. However, if the laser beam L1 emitted from the laser light source 2 is sufficiently parallelized, for example, if a gas laser such as a He-Ne laser is used as the laser light source 2, the collimating lens 85 may be omitted.

[0052] On the other hand, if the laser light source 2 is a semiconductor laser element, it is preferable to provide a collimating lens 85. This makes the laser light L1 collimated, which suppresses the need to enlarge the various optical components that receive the laser light L1, and thus allows for miniaturization of the laser interferometer 1.

[0053] The collimated laser light L1 passes through the half-wave plate 81, where it is converted into linearly polarized light with a P-polarized to S-polarized intensity ratio of, for example, 50:50, and is then incident on the first light splitter 41.

[0054] 1.1.3. Shielding elements The shielding element 86 is an aperture positioned between the collimating lens 85 and the second optical splitter 42. The shielding element 86 has an opening provided corresponding to the optical path 17. As shown in Figure 2, the shielding element 86 more reliably suppresses the incidence of reflected light L4 and L5 into the emission section of the laser light source 2. The shielding element 86 can be any member with a slit, pinhole, or the like, and its structure is not particularly limited. Furthermore, the shielding element 86 may be provided only as needed, and may be omitted if the incidence of reflected light L4 and L5 into the emission section can be suppressed without the shielding element 86.

[0055] 1.1.4.First light splitter The first optical splitter 41 is, for example, a polarized beam splitter. The first optical splitter 41 has the function of transmitting P-polarized light and reflecting S-polarized light. Through this function, the first optical splitter 41 reflects a portion of the laser light L1 to generate the first light L1a, and transmits the other portion of the laser light L1 to generate the second light L1b.

[0056] The first light L1a is converted to circular polarization by the quarter-wave plate 83 and incident on the optical modulator 12. The first light L1a incident on the optical modulator 12 is f m It undergoes a frequency shift of [Hz] and is reflected as reference light L2. Therefore, reference light L2 has a frequency f mIt contains a modulation component of [Hz]. When the reference light L2 passes through the quarter-wave plate 83, it is converted to P-polarized light and incident on the first light divider 41.

[0057] The second light L1b is converted to circular polarization by the quarter-wave plate 82 and incident on the object 14. The second light L1b incident on the object 14 is f d It undergoes a Doppler shift of [Hz] and is reflected as object light L3. Therefore, object light L3 has a frequency f d It contains a sample-derived component of [Hz]. When the object light L3 passes through the quarter-wave plate 82, it is converted to S-polarization and incident on the first light divider 41.

[0058] The first light splitter 41 also has the function of mixing the reference light L2 and the object light L3. The mixed reference light L2 and object light L3 pass through the analyzer 84 and are incident on the first photodetector 10.

[0059] Furthermore, a non-polarizing beam splitter may be used instead of a polarizing beam splitter for the first optical splitter 41. In this case, the half-wave plate 81, quarter-wave plate 82, and quarter-wave plate 83, etc., become unnecessary, thus reducing the number of parts and allowing for miniaturization of the laser interferometer 1. Alternatively, an optical splitter other than a beam splitter may be used.

[0060] Since S-polarized and P-polarized light, which are orthogonal to each other, are independent of each other, simply superimposing them will not produce beats due to interference. Therefore, the mixed reference light L2 and object light L3 are passed through an analyzer 84 tilted at 45° with respect to both the S-polarized and P-polarized light. By using the analyzer 84, light with common components can be transmitted, causing interference. As a result, the reference light L2 and object light L3 interfere well, and |f m -f d Interfering light with a frequency of |[Hz] is generated.

[0061] 1.1.5. First photodetector When interfering light is incident on the first photodetector 10, the first photodetector 10 outputs a photocurrent (received signal) corresponding to the intensity of the interfering light (received intensity). By demodulating the sample-derived component from this received signal using a method described later, the movement of the object 14, i.e., displacement and velocity, can be determined. Examples of the first photodetector 10 include a photodiode. Note that the light received by the first photodetector 10 does not need to be light containing both sample-derived components and modulation components, and is not limited to interfering light produced by the above-described path. Furthermore, "demodulating the sample-derived component from the received signal" in this specification includes demodulating the sample-derived component after performing various processing on the photocurrent (received signal).

[0062] 1.1.6. Optical Modulator Next, the optical modulator 12 will be described.

[0063] The optical modulator 12 operates based on the drive signal Sd input from the signal generation unit 60, shifting the frequency of the laser light L1. Examples of such optical modulators 12 include acousto-optic modulators (AOMs), electro-optic modulators (EOMs), semiconductor optical modulators, and oscillator-type optical modulators.

[0064] As shown in Figures 1 and 2, an oscillator-type optical modulator having a vibrating element 30 is preferably used for the optical modulator 12. The oscillator-type optical modulator is an optical modulator having a vibrating element, such as the one disclosed in Japanese Patent Application Publication No. 2022-38156, and has a vibrating element 30, which is used to shift the frequency of the laser light L1. Examples of vibrating elements 30 include a quartz crystal resonator, a silicon resonator, a ceramic resonator, etc. By using such a vibrating element 30, the optical modulator 12 can be made smaller, lighter, and more power-efficient.

[0065] 1.1.7.Second light splitter The second optical splitter 42 is, for example, an unpolarized beam splitter. The unpolarized beam splitter may be cube-shaped, plate-shaped, or of any other shape. The second optical splitter 42 splits the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3 at predetermined splitting ratios, regardless of polarization. The splitting ratio of the second optical splitter 42 is not particularly limited, but is preferably set so that the amount of light heading towards the laser light source 2 is greater than the amount of light heading towards the second photodetector 32. In other words, it is preferable that the splitting ratios of the reflected light L4 and reflected light L5 are set so that the optical path 19 (second optical path) is smaller than the optical path 17 (first optical path). This allows the amount of light heading towards the first optical splitter 41 to be increased even when the laser light L1 emitted from the laser light source 2 is split by the second optical splitter 42. As a result, the amount of light of the reference light L2 and object light L3 received by the first photodetector 10 can be increased. On the other hand, when the reflected light L4 and L5 are split by the second light splitter 42, the amount of light directed toward the laser light source 2 becomes relatively larger, and the amount of light directed toward the second photodetector 32 becomes relatively smaller. However, since the second photodetector 32 can acquire the light detection position even if the amount of reflected light L4 and L5 is small, there is little problem.

[0066] The division ratio in the second optical splitter 42 is set such that the value of I2 / I1, which is the ratio of the amount of light I2 heading towards the optical path 19 (second optical path) to the amount of light I1 of the return light L4 and L5 heading towards the optical path 17 (first optical path), is preferably 1 / 99 or more and 50 / 50 or less, and more preferably 5 / 95 or more and 30 / 70 or less.

[0067] Furthermore, it is preferable that the optical path length OL1 of optical path 17 (first optical path) and the optical path length OL2 of optical path 19 (second optical path) are the same. This ensures that the destination position of the reflected light L4 and L5 when they return along optical path 17 coincides with the destination position of the reflected light L4 and L5 when they return along optical path 19. In other words, the latter destination position reflects the former destination position. Therefore, by detecting the latter destination position with the second photodetector 32, the former destination position can be monitored more accurately. This makes it easy to detect when the reflected light L4 and L5 return to the laser light source 2, allowing for more efficient optical axis adjustment.

[0068] The optical path length OL1 is preferably the optical distance from the intersection of the optical splitting surface of the second optical splitter 42 and the optical path 17 to the shielding element 86. The optical path length OL2 is preferably the optical distance from the intersection of the optical splitting surface of the second optical splitter 42 and the optical path 19 to the light-receiving surface of the second light-receiving element 32.

[0069] 1.1.8. Second photodetector The second light-receiving element 32 is positioned in the optical path 19 (second optical path) and receives the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3, which have been divided by the second light divider 42. This allows the reception positions of the reflected light L4 and L5 to be obtained.

[0070] The second light-receiving element 32 is a light-receiving element capable of acquiring a one-dimensional or two-dimensional distribution of the intensity of the received light. Examples of such light-receiving elements include CCDs (Charge Coupled Devices), CMOS (Complementary Metal Oxide Semiconductors), line sensors, and area sensors. Of these, a light-receiving element capable of acquiring a two-dimensional distribution is preferably used. This allows for more accurate acquisition of the light-receiving position, making it easier for the user to adjust the optical axis.

[0071] Furthermore, the second light-receiving element 32 may have the function of acquiring not only the light-receiving position but also the light-receiving intensity. This allows the user to adjust the optical axis while taking into account not only the light-receiving position but also the light-receiving intensity. As a result, more accurate optical axis adjustment can be performed efficiently.

[0072] 1.2. Signal Generation Unit The signal generation unit 60 shown in Figure 1 outputs a drive signal input to the optical modulator 12 and a reference signal input to the demodulation calculation unit 52.

[0073] In this embodiment, as shown in Figure 1, the signal generation unit 60 includes an oscillation circuit 61. The oscillation circuit 61 operates using the vibration element 30 as a signal source and generates a highly accurate periodic signal. As a result, the oscillation circuit 61 outputs a highly accurate drive signal and a reference signal. Consequently, when disturbances occur, the drive signal and the reference signal are affected in the same way. Therefore, the modulation component added via the vibration element 30 driven by the drive signal, and the reference signal are also affected in the same way. For this reason, when the modulation component and the reference signal are subjected to calculations in the demodulation calculation unit 52, the effects of disturbances contained in both can be canceled out or reduced during the calculation process. As a result, the robustness of the demodulation calculation unit 52 against disturbances can be increased. Furthermore, the laser interferometer 1 can be made smaller, lighter, and consume less power.

[0074] An example of the oscillator circuit 61 is the oscillator circuit disclosed in Japanese Patent Application Publication No. 2022-38156.

[0075] Furthermore, the signal generation unit 60 may be equipped with a signal generator such as a function generator or a signal generator instead of the oscillation circuit 61.

[0076] 1.3. Enclosure Figure 3 is an example of an external view of the sensor head unit 71 shown in Figure 1.

[0077] The sensor head unit 71 shown in Figure 3 includes a housing 70. The housing 70 houses the interference optical system 50 and the signal generation unit 60. In other words, the housing 70 houses at least the laser light source 2, the first optical splitter 41, the optical modulator 12, the first photodetector 10, the second optical splitter 42, and the second photodetector 32. This protects the interference optical system 50 and the signal generation unit 60 from foreign objects, external forces, environmental changes, etc. It also allows the user to easily grasp the sensor head unit 71 and change its attitude and position.

[0078] The external shape of the housing 70 is not limited to the rectangular parallelepiped shown in the figure, but may be any shape. Examples of materials that make up the housing 70 include resin materials, metal materials, glass materials, etc. Alternatively, it may be a composite material formed by combining two or more of these materials.

[0079] 1.4. Demodulation Calculation Unit The demodulation calculation unit 52 shown in Figure 1 includes a pre-processing unit 53 and a demodulation processing unit 54.

[0080] For example, the pre-processing unit 53 and demodulation unit disclosed in Japanese Patent Application Publication No. 2022-38156 can be applied to the pre-processing unit 53 and demodulation unit 54.

[0081] The preprocessing unit 53 performs preprocessing on the received light signal based on the reference signal Ss. The preprocessing involves splitting the received light signal into two signals, multiplying one of them by the reference signal, and then summing the two signals to output the preprocessed signal.

[0082] The demodulation processing unit 54 demodulates the sample-derived components corresponding to the velocity and position of the object 14 from the pre-processed signal output from the pre-processing unit 53, based on the reference signal Ss.

[0083] Furthermore, the demodulation processing unit 54 calculates the position of the object 14 from the sample-derived components, specifically the phase information derived from the object 14 contained in the pre-processed signal. In this case, the laser interferometer 1 is used as a displacement meter. The demodulation processing unit 54 also determines the velocity from the change in the position of the object 14. In this case, the laser interferometer 1 is used as a velocity meter.

[0084] 1.5. Light receiving position display section The light-receiving position display unit 56 shown in Figure 1 displays the light-receiving positions of the reflected light L4 and L5 acquired by the second light-receiving element 32. Preferably, the light-receiving positions are displayed in real time or at a similar timing. This allows the user to easily recognize the relative relationship between the housing 70 and the object 14 from the light-receiving positions of the reflected light L4 and L5, thereby reducing the difficulty of optical axis adjustment.

[0085] Examples of the light-receiving position indicator unit 56 include liquid crystal display panels, organic EL (Electro-Luminescence) display panels, and image projectors. Furthermore, the light-receiving position indicator unit 56 may utilize a display device that has the function of indicating the light-receiving position using, for example, changes in light emission amount or volume, changes in shapes or patterns, sounds, or characters. The light-receiving position indicator unit 56 also includes a function of generating image signals, etc., in order to display images, etc., on these display devices.

[0086] Furthermore, the light-receiving position display unit 56 may have the function of displaying not only the light-receiving position but also the light-receiving intensity. This allows the user to adjust the optical axis while taking into account not only the light-receiving position but also the light-receiving intensity. As a result, more accurate optical axis adjustment can be performed efficiently.

[0087] 1.6. AC Level Acquisition Section The AC level acquisition unit 57 shown in Figure 1 acquires the AC level resulting from the interference between the reference light L2 and the object light L3 contained in the received light signal. The received light signal resulting from the interference between the reference light L2 and the object light L3 contains a direct current (DC) component and an alternating current (AC) component. The AC level acquisition unit 57 acquires the intensity (AC level) of the AC component contained in the received light signal. The AC level is acquired, for example, by detecting the envelope of the received light signal and quantifying the amplitude of the detected envelope.

[0088] 1.7. AC Level Display Unit The AC level display unit 58 shown in Figure 1 displays the AC level acquired by the AC level acquisition unit 57. The AC level increases when the beam of reference light L2 and the beam of object light L3 overlap on the light-receiving surface of the first light-receiving element 10, and when the optical axis of the reference light L2 and the optical axis of the object light L3 become parallel. Therefore, the user can efficiently perform the above adjustment operation by adjusting the optical axis while recognizing the AC level.

[0089] Examples of the AC level display unit 58 include liquid crystal display panels, organic EL display panels, and image projectors. The AC level display unit 58 may also utilize a display device that has the function of displaying the AC level using, for example, changes in light output or volume, changes in shapes or patterns, sounds, or characters. The AC level display unit 58 also includes a function for generating image signals, etc., in order to display images, etc., on these display devices.

[0090] Furthermore, the AC level display unit 58 may be integrated with the light receiving position display unit 56. In other words, the same display device may be configured to display both the light receiving position and the AC level. This allows the user to simultaneously view the light receiving position and the AC level, enabling them to operate while relating the two. As a result, the accuracy and reliability of operation can be improved.

[0091] 1.8. Operation Instruction Unit The operation teaching unit 59 shown in Figure 1, when the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3 are each received by the second light receiving element 32, instructs the user on how to change the relative relationship between the housing 70 and the object 14 based on the respective light receiving positions. By providing such an operation teaching unit 59, even inexperienced users can efficiently adjust the optical axis. The teaching method is not particularly limited, but examples include changing the amount of light emitted or the volume, changing shapes or patterns, or using sounds or text.

[0092] Furthermore, the operation instruction unit 59 may have a function to superimpose the content of the instruction onto the light-receiving position display unit 56. This allows the user to simultaneously view the light-receiving position and the content of the instruction, enabling them to perform operations according to the instruction while simultaneously viewing the light-receiving position that represents the result. As a result, the accuracy and reliability of the operation can be improved. The operation instruction unit 59 may be provided as needed, but may be omitted.

[0093] 1.9. Hardware Configuration The functions of the demodulation calculation unit 52, the AC level acquisition unit 57, and the operation teaching unit 59 are realized by hardware, such as a processor, memory, external interface, and input unit. Specifically, they are realized by the processor reading and executing a program stored in memory. These components can communicate with each other via an external bus.

[0094] Examples of processors include CPUs (Central Processing Units) and DSPs (Digital Signal Processors). Alternatively, instead of these processors executing software, FPGAs (Field-Programmable Gate Arrays) or ASICs (Application-Specific Integrated Circuits) may be used to implement the aforementioned functions.

[0095] Examples of memory include HDD (Hard Disk Drive), SSD (Solid State Drive), EEPROM (Electrically Erasable Programmable Read-Only Memory), ROM (Read-Only Memory), and RAM (Random Access Memory).

[0096] External interfaces include, for example, digital input / output ports such as USB (Universal Serial Bus), Ethernet® ports, wireless LAN (Local Area Network), and Bluetooth®.

[0097] Examples of input devices include keyboards, mice, touch panels, and touchpads.

[0098] External interfaces and input sections may be provided as needed, but may be omitted.

[0099] 2. Method for adjusting the optical axis of a laser interferometer Next, a method for adjusting the optical axis of the laser interferometer according to the embodiment will be described. In the following description, the method for adjusting the optical axis of the laser interferometer 1 described above will be used as an example.

[0100] Figure 4 is a flowchart showing the configuration of the optical axis adjustment method for a laser interferometer according to an embodiment.

[0101] In step S102 shown in Figure 4, the second light-receiving element 32 receives the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3. As a result, the second light-receiving element 32 obtains the respective reception positions for the reflected light L4 and L5.

[0102] In step S104, the light reception position display unit 56 displays the light reception positions of the reflected light L4 and L5 acquired by the second light receiving element 32.

[0103] Figure 5 shows an example of the light receiving positions of the reflected light L4 and L5 and the warning range Z1 displayed on the light receiving position display unit 56.

[0104] As shown in Figure 5, the receiving position of the reflected light L4 is located approximately in the center of the receiving position indicator unit 56. In contrast, the receiving position of the reflected light L5 shown in Figure 5 is an example of the position before optical axis adjustment. When adjusting the optical axis of the laser interferometer 1, it is preferable to first move the reflected light L5 to a predetermined starting point SP, and then perform an operation to scan in a predetermined direction.

[0105] Therefore, in step S106, the reflected light L5 of the object light L3 is guided to the starting point SP. In Figure 5, symbol T1 is shown, which indicates the instruction to guide the reflected light L5 to the starting point SP. Symbol T1 is an arrow-shaped figure that indicates the direction and distance to move the reflected light L5 to the starting point SP.

[0106] Furthermore, Figure 5 shows the base point BP. The base point BP represents the position where the reflected light L4 returns to the laser light source 2 when the light input / output surface of the optical modulator 12 is not tilted. Therefore, if the receiving position of the reflected light L4 is shifted from the base point BP as shown in Figure 5, it can be seen that the light input / output surface of the optical modulator 12 is tilted.

[0107] Furthermore, in Figure 5, a warning range Z1 is set around the base point BP. The warning range Z1 indicates the area where reflected light L4 and L5 may enter and potentially be incident on the laser light source 2. The light receiving position display unit 56 has this warning range Z1 stored in advance, and by displaying it, the probability of accidentally causing reflected light L4 and L5 to be incident on the laser light source 2 during optical axis adjustment can be reduced.

[0108] In step S108, the user performs a modification operation to change the orientation of the housing 70 based on the instruction from the operation instruction unit 59. This allows the return light L5 shown in Figure 5 to be moved to the starting point SP.

[0109] Figure 6 shows an example of how the operation teaching unit 59 teaches the user to change the orientation of figure 70a, which mimics the housing 70, to the orientation of figure 70b. In Figure 6, the change in the orientation of the housing 70 is taught by displaying figures 70a and 70b, which mimic the housing 70, and an arrow-shaped symbol T2 on the light-receiving position display unit 56. By providing this type of teaching, even inexperienced users can efficiently perform the change operation.

[0110] Step S110 guides the scanning operation from the starting point SP. Figure 7 is a table summarizing the relationship between the three positions through which the reflected light L5, displayed on the light-receiving position indicator 56 shown in Figure 5, passes during the scanning operation, and the corresponding AC level, the incident direction of the reference light L2 and object light L3, the interference image, positional shift, angular shift, and the presence or absence of interference fringes at each position. In Figure 7, the incident directions of the reference light L2 and object light L3 incident on the first light-receiving element 10 are represented by arrows, and the illumination surfaces of the reference light L2 and object light L3 irradiated onto the first light-receiving element 10 are represented by ellipses. The incident direction of the reference light L2 is represented by a relatively dark arrow, and the incident direction of the object light L3 is represented by a relatively light arrow. The illumination surface of the reference light L2 is represented by a relatively dark ellipse, the illumination surface of the object light L3 is represented by a relatively light ellipse, and the overlapping region of the illumination surfaces is represented by the darkest ellipse.

[0111] In step S110, as shown in Figure 7, the scanning operation is guided by displaying an arrow-shaped symbol T3 on the light receiving position display unit 56, which moves the reflected light L5 from the starting point SP in the scanning direction.

[0112] In step S112, while performing a scan operation, the AC level acquisition unit 57 acquires the AC level during the operation, and the AC level display unit 58 displays the AC level.

[0113] In the scan operation, the maximum point of the AC level is searched for by moving the return light L5 from the starting point SP toward the opposite side of the base point BP. In other words, the operation continuously changes the relative relationship between the housing 70 and the object 14.

[0114] The graph shown in Figure 7 illustrates the relationship between the distance from the base point BP and the AC level during a scan operation. The relationship between distance and AC level shown in Figure 7 is represented by a graph with local maxima. The scan operation may be an operation that continuously changes the orientation of the housing 70, or an operation that changes it discontinuously.

[0115] When the reflected light L5 is at the starting point SP, the reference light L2 and the object light L3 overlap on the light-receiving surface of the first photodetector 10. However, the incident direction of the reference light L2 and the incident direction of the object light L3 are not parallel. That is, when the angle between the two incident directions is θ, θ ≠ 0. In this case, there is no positional misalignment between the reference light L2 and the object light L3, but there is an angular misalignment, which causes interference fringes to occur on the light-receiving surface. These interference fringes reduce the AC level and cause a decrease in the signal-to-noise ratio (S / N ratio) of the received signal. Therefore, it can be said that the presence or absence of interference fringes cannot be evaluated based solely on the presence or absence of positional misalignment, and it is necessary to detect the presence or absence of angular misalignment.

[0116] Therefore, in step S112, the receiving positions of the reflected light L4 and L5 are checked, and the optical axis is adjusted while checking the AC level. This allows the user to understand the relationship between the receiving position and the AC level while making adjustments, thus enabling more efficient optical axis adjustment. In other words, by checking the AC level displayed on the AC level display unit 58 and moving the reflected light L5 from the starting point SP in a predetermined direction (scan operation), the point of maximum AC level can be easily searched.

[0117] In the graph of Figure 7, the AC level is maximized when the reflected light L5 coincides with position P1. The maximum point shown in Figure 7 exceeds a preset threshold. Therefore, position P1 can be considered a position where a sufficient AC level can be obtained. When the reflected light L5 is at position P1, the positional misalignment between the reference light L2 and the object light L3 on the light-receiving surface of the first photodetector 10 is small, and there is no angular misalignment. Therefore, the angle θ between the two incident directions satisfies θ=0, and no interference fringes are generated. In this case, the optical axis adjustment of the laser interferometer 1 can be considered complete.

[0118] Furthermore, during scanning operations, it is preferable that the AC level display unit 58 has a light emitter whose color changes in conjunction with the AC level. Figure 7 shows an example where the light emitter is illuminated in blue when the reflected light L5 is at the starting point SP. By visually observing this color change, the user can intuitively recognize that the reflected light L5 is at the starting point SP, thereby enabling more efficient optical axis adjustment.

[0119] Furthermore, it is preferable that the light emitter emits a different color when the AC level exceeds a threshold. In other words, it is preferable that the light emitter of the AC level display unit 58 changes color according to the AC level. Figure 7 shows an example where the light emitter emits green when the reflected light L5 is at position P1. This allows the user to intuitively recognize that the AC level has exceeded a threshold. Note that it is not necessarily required to search for a local maximum; it is sufficient to search for a position where the AC level exceeds the threshold.

[0120] On the other hand, if the receiving position of the reflected light L5 is within the warning range Z1, it is preferable to emit a different color from the light emitter. For example, when the reflected light L5 is within the warning range Z1, it is preferable to emit red light from the light emitter. This allows the user to intuitively recognize that the reflected light L5 is within the warning range Z1.

[0121] In step S114, it is determined whether the AC level is above a threshold (whether a predetermined condition is met). When the return light L5 is at position P1 as shown in Figure 7, the AC level is above the threshold (Yes), so the process proceeds to step S116 and the scan operation ends. On the other hand, when the return light L5 is between the starting point SP and position P1 as shown in Figure 7, the AC level is below the threshold (No), so the process returns to step S112 and the scan operation continues.

[0122] Furthermore, consider the case where the reflected light L5 moves beyond position P1 shown in Figure 7 in the scanning direction and reaches position P2. In this case, the positional misalignment between the reference light L2 and the object light L3 is large, and the angular misalignment is also large, on the light-receiving surface of the first light-receiving element 10. Interference fringes are also generated on the light-receiving surface, and the AC level is below the threshold. In such a case as well, the process returns to step S112 and the scanning operation continues.

[0123] Furthermore, if the AC level is below the threshold, it is preferable to make the light emitter emit a color different from any of the above. Figure 7 shows an example where the light emitter emits yellow when the AC level is below the threshold. This allows the user to intuitively recognize that the AC level is insufficient.

[0124] According to the method described above, even inexperienced users can efficiently adjust the optical axis to suppress the generation of interference fringes. This makes it possible to suppress the decrease in the signal-to-noise ratio of the received signal in the laser interferometer 1.

[0125] 3. First variation Next, a laser interferometer according to a first modified example of the above embodiment will be described.

[0126] Figure 8 is a schematic diagram showing the interference optical system 50 of the laser interferometer 1 according to the first modified example.

[0127] The following describes the first modified example, focusing on the differences from the above embodiment, and omitting explanations of similar items. In Figure 8, components similar to those in the above embodiment are denoted by the same reference numerals.

[0128] The laser interferometer 1 shown in Figure 8 is the same as the laser interferometer 1 shown in Figure 2, except that the configuration of the interference optical system 50 is different.

[0129] In the interference optical system 50 shown in Figure 2, the laser light L1 emitted from the laser light source 2 propagates along the optical path 17, and a portion of it is reflected by the second optical splitter 42 and travels along the optical path 18. The reflected light L4 and L5 propagates along the optical path 18, and a portion of it passes through the second optical splitter 42 and is received by the second photodetector 32.

[0130] In contrast, in the interference optical system 50 shown in Figure 8, the laser light L1 emitted from the laser light source 2 propagates along the optical path 17, and then a portion of it passes through the second optical splitter 42 and proceeds along the optical path 18. The reflected light L4 and L5 propagates along the optical path 18, and a portion of it is reflected by the second optical splitter 42 and received by the second photodetector 32.

[0131] Therefore, in the laser interferometer 1 shown in Figure 8, just like in the laser interferometer 1 shown in Figure 2, the optical axis adjustment to suppress the generation of interference fringes can be performed efficiently. In this first modified example, the same effects as in the above embodiment can be obtained.

[0132] 4. Second variation Next, a laser interferometer according to a second modified example of the above embodiment will be described.

[0133] Figure 9 is a schematic diagram showing the interference optical system 50 of the laser interferometer 1 according to the second modified example.

[0134] The following describes a second modified example, focusing on the differences from the above embodiment, and omitting explanations of similar aspects. In Figure 9, components similar to those in the above embodiment are denoted by the same reference numerals.

[0135] The laser interferometer 1 shown in Figure 9 is the same as the laser interferometer 1 shown in Figure 2, except that the configuration of the interference optical system 50 is different.

[0136] In the interference optical system 50 shown in Figure 9, a triangular prism is used as the second optical splitter 42. This second optical splitter 42, composed of a triangular prism, has an external reflective surface 421 and an internal reflective surface 422. The external reflective surface 421 has the function of reflecting a portion of the laser light L1 and transmitting a portion of the reflected light L4 and L5. The internal reflective surface 422 has the function of reflecting the reflected light L4 and L5 that has passed through the external reflective surface 421. The reflected light L4 and L5 reflected by the internal reflective surface 422 is received by the second photodetector 32. In this second modified example, the same effects as in the above embodiment can be obtained.

[0137] 5. Effects of the above embodiments and modifications As described above, the laser interferometer 1 according to the above embodiment and modified example comprises a laser light source 2, a first optical splitter 41, an optical modulator 12, a first light receiving element 10, a second optical splitter 42, a second light receiving element 32, a light receiving position display unit 56, an AC level acquisition unit 57, and an AC level display unit 58. The laser light source 2 emits laser light L1. The first optical splitter 41 splits the laser light L1 into a first light L1a and a second light L1b. The optical modulator 12 modulates the frequency of the first light L1a to generate a reference light L2. The first light receiving element 10 receives object light L3 generated when the reference light L2 and the second light L1b are irradiated onto the object 14, and outputs a light receiving signal based on the light receiving intensity. The second optical splitter 42 is positioned on the optical paths 17 and 18 connecting the laser light source 2 and the first optical splitter 41, and guides the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3 generated in the first optical splitter 41 to an optical path 19 (second optical path) different from the optical path 17 (first optical path) leading to the laser light source 2. The second photodetector 32 is positioned in the optical path 19 and acquires the reception position of the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3. The photodetector position display unit 56 displays the acquired photodetector position. The AC level acquisition unit 57 acquires the AC level due to the interference between the reference light L2 and the object light L3 included in the received signal. The AC level display unit 58 displays the acquired AC level.

[0138] With this configuration, the optical axis can be efficiently adjusted to suppress the generation of interference fringes, and a laser interferometer 1 can be realized that can suppress the decrease in the signal-to-noise ratio of the received light signal.

[0139] The laser interferometer 1 may include a housing 70 and an operation teaching unit 59. The housing 70 houses a laser light source 2, a first optical splitter 41, an optical modulator 12, a first photodetector 10, a second optical splitter 42, and a second photodetector 32. The operation teaching unit 59 teaches modification operations to change the relative relationship between the housing 70 and the object 14 based on the reception positions of the reflected light L4 and L5.

[0140] With this configuration, even inexperienced users can efficiently adjust the optical axis.

[0141] In the laser interferometer 1, the operation teaching unit 59 may teach a scan operation that changes the relative relationship between the housing 70 and the object 14. In this case, the AC level acquisition unit 57 acquires the change in the AC level while the scan operation is being performed.

[0142] With this configuration, users can perform adjustments while understanding the relationship between the light receiving position and the AC level, thus enabling more efficient optical axis adjustment.

[0143] In the laser interferometer 1, the operation teaching unit 59 may teach a change operation to guide the receiving position of the reflected light L5 of the object light L3 to the starting point SP of the scan operation.

[0144] With this configuration, the maximum AC level can be easily searched by scanning the reflected light L5 in a predetermined direction from the starting point SP.

[0145] In the laser interferometer 1, the operation teaching unit 59 may change the content of the teaching according to the AC level. With this configuration, the user can intuitively perceive the AC level.

[0146] In the laser interferometer 1, the operation teaching unit 59 may change the content of the teaching when the AC level exceeds a threshold.

[0147] With this configuration, users can intuitively recognize when the AC level exceeds the threshold.

[0148] In the laser interferometer 1, the light receiving position display unit 56 may pre-store as a warning range Z1 the range in which the reflected light L5 of the object light L3 affects the laser light source 2. In this case, when the light receiving position of the reflected light L5 enters the warning range Z1, the operation teaching unit 59 may change the content of the teaching.

[0149] This configuration reduces the probability of accidentally directing reflected light L4 and L5 into the laser light source 2.

[0150] In the laser interferometer 1, the light receiving position display unit 56 may display the content of the instruction given by the operation instruction unit 59.

[0151] With this configuration, the user can simultaneously view the light-receiving position and the content of the instruction, allowing them to reflect the instruction in their operation and confirm the results. As a result, the accuracy and reliability of the operation can be improved.

[0152] In the laser interferometer 1, it is preferable that the division ratios of the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3 in the second optical splitter 42 are smaller in optical path 19 (second optical path) than in optical path 17 (first optical path).

[0153] With this configuration, even when the laser light L1 is split by the second optical splitter 42, the amount of light directed towards the first optical splitter 41 can be increased. As a result, the amount of reference light L2 and object light L3 received by the first photodetector 10 can be increased. On the other hand, when the reflected light L4 and L5 are split by the second optical splitter 42, the amount of light directed towards the laser light source 2 becomes relatively larger, and the amount of light directed towards the second photodetector 32 becomes relatively smaller. However, since the second photodetector 32 can acquire the reception position even if the amount of reflected light L4 and L5 is small, there is little problem.

[0154] In the laser interferometer 1, it is preferable that the optical path length OL1 of optical path 17 (first optical path) and the optical path length OL2 of optical path 19 (second optical path) are the same.

[0155] With this configuration, the destination positions of the reflected light L4 and L5 when they return along the optical path 17 coincide with the destination positions of the reflected light L4 and L5 when they return along the optical path 19. In other words, the latter destination position reflects the former destination position. Therefore, by detecting the latter destination position with the second photodetector 32, the former destination position can be monitored more accurately.

[0156] The optical axis adjustment method for the laser interferometer according to the above embodiment is a method for adjusting the optical axis of the laser interferometer 1. The laser interferometer 1 comprises a laser light source 2, a first optical splitter 41, an optical modulator 12, a first photodetector 10, a second optical splitter 42, and a second photodetector 32. The laser light source 2 emits laser light L1. The first optical splitter 41 splits the laser light L1 into a first optical beam L1a and a second optical beam L1b. The optical modulator 12 modulates the frequency of the first optical beam L1a to generate a reference beam L2. The first photodetector 10 receives object light L3 generated when the reference beam L2 and the second optical beam L1b are irradiated onto an object 14, and outputs a received signal based on the received light intensity. The second optical splitter 42 is positioned on the optical paths 17 and 18 connecting the laser light source 2 and the first optical splitter 41, and guides the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3 generated in the first optical splitter 41 to an optical path 19 (second optical path) that is different from the optical path 17 (first optical path) leading to the laser light source 2. The second photodetector 32 is positioned in the optical path 19 and acquires the respective receiving positions for the reflected light L4 of the reference light L2 and the reflected light L5 of the object light L3.

[0157] The optical axis adjustment method of the laser interferometer according to the above embodiment includes steps S108, S112, and S116. In step S108, a modification operation is performed to change the relative relationship between the laser interferometer 1 and the object 14 based on the light receiving position acquired by the second light receiving element 32, thereby moving the light receiving position of the reflected light L5 of the object light L3 to the starting point. In step S112, while performing a scan operation that continuously changes the relative relationship from the starting point, the AC level due to the interference between the reference light L2 and the object light L3 included in the received signal is acquired. In step S116, when the acquired AC level satisfies a predetermined condition, the scan operation is terminated.

[0158] With this configuration, the optical axis of the laser interferometer 1 can be efficiently adjusted to suppress the generation of interference fringes.

[0159] Although the laser interferometer according to the present invention has been described above based on the illustrated embodiment, the laser interferometer according to the present invention is not limited to the above embodiment, and the configuration of each part can be replaced with any configuration having a similar function. Furthermore, other arbitrary components may be added to the laser interferometer according to the above embodiment. Moreover, the optical axis adjustment method of the laser interferometer according to the present invention may have additional steps for any purpose added to the above embodiment.

[0160] The laser interferometer according to the present invention can be applied not only to the displacement meters and speedometers mentioned above, but also to, for example, vibration meters, inclinometers, distance meters (length measuring instruments), etc. Furthermore, applications of the laser interferometer according to the present invention include optical comb interferometry technology that enables distance measurement, 3D imaging, spectroscopy, etc., optical fiber gyroscopes that realize angular velocity sensors, angular acceleration sensors, etc., and Fourier spectrometers equipped with moving mirror devices.

[0161] Furthermore, two or more of the laser light source, optical modulator, first photodetector, and second photodetector may be mounted on the same substrate. This facilitates miniaturization and weight reduction of the interference optical system, as well as improving ease of assembly.

[0162] Furthermore, although the above embodiment has a so-called Michelson-type interference optical system, the laser interferometer according to the present invention is also applicable to other types of interference optical systems, such as those having a Mach-Zehnder-type interference optical system. [Explanation of symbols]

[0163] 1…Laser interferometer, 2…Laser light source, 10…First photodetector, 12…Optical modulator, 14…Object, 17…Optical path, 18…Optical path, 19…Optical path, 20…Optical path, 22…Optical path, 24…Optical path, 30…Vibrating element, 32…Second photodetector, 41…First optical splitter, 42…Second optical splitter, 50…Interference optical system, 52…Demodulation calculation unit, 53…Preprocessing unit, 54…Demodulation processing unit, 56…Photodetector position display unit, 57…AC level acquisition unit, 58…AC level display unit, 59…Operation teaching unit, 60…Signal generation unit, 61…Oscillation circuit, 70…Housing, 70a…Figure, 70b…Figure, 71…Sensor head unit, 72…Main unit, 81…Half wave plate, 82…Quarter wave plate, 8 3...Quarter wave plate, 84...Analyzer, 85...Collimating lens, 86...Shielding element, 421...External reflecting surface, 422...Internal reflecting surface, BP...Base point, L1...Laser light, L1a...First light, L1b...Second light, L2...Reference light, L3...Object light, L4...Return light, L5...Return light, OL1...Optical path length, OL2...Optical path length, P1...Position, P2...Position, S102...Step, S104...Step, S106...Step, S108...Step, S110...Step, S112...Step, S114...Step, S116...Step, SP...Starting point, Sd...Drive signal, Ss...Reference signal, T1...Symbol, T2...Symbol, T3...Symbol, Z1...Warning range, θ...Angle

Claims

1. A laser light source that emits laser light, A first light splitter that splits the aforementioned laser light into a first light and a second light, A light modulator that modulates the frequency of the first light and generates a reference light, A first light-receiving element that receives object light generated when the reference light and the second light are irradiated onto an object, and outputs a light-receiving signal based on the light-receiving intensity, A second optical splitter is positioned on the optical path connecting the laser light source and the first optical splitter, and guides the return light of the reference light and the return light of the object light generated in the first optical splitter to a second optical path different from the first optical path toward the laser light source. A second light-receiving element is arranged in the second optical path and acquires the respective light-receiving positions for the reflected light of the reference light and the reflected light of the object light, A light-receiving position display unit that displays the acquired light-receiving position, An AC level acquisition unit that acquires the AC level due to the interference between the reference light and the object light included in the received light signal, An AC level display unit that displays the acquired AC level, A laser interferometer characterized by being equipped with the following features.

2. A housing that houses the laser light source, the first optical splitter, the optical modulator, the first photodetector, the second optical splitter, and the second photodetector, An operation teaching unit that teaches a modification operation to change the relative relationship between the housing and the object based on the light receiving position, A laser interferometer according to claim 1, comprising:

3. The operation teaching unit teaches a scan operation that changes the relative relationship, The laser interferometer according to claim 2, wherein the AC level acquisition unit acquires the change in the AC level during the scan operation.

4. The laser interferometer according to claim 3, wherein the operation teaching unit teaches the modification operation so as to guide the receiving position of the reflected light of the object light to the starting point of the scan operation.

5. The laser interferometer according to claim 2, wherein the operation teaching unit changes the content of the teaching according to the AC level.

6. The laser interferometer according to claim 5, wherein the operation teaching unit changes the content of the teaching when the AC level exceeds a threshold.

7. The light receiving position display unit pre-stores as a warning range the range in which the reflected light of the object affects the laser light source. The laser interferometer according to claim 2, wherein when the light receiving position enters the warning range, the operation teaching unit changes the content of the teaching.

8. The laser interferometer according to claim 2, wherein the light receiving position display unit displays the content of the teaching by the operation teaching unit.

9. The laser interferometer according to claim 1, wherein the division ratio of the return light of the reference light and the return light of the object light in the second optical splitter is smaller for the second optical path than for the first optical path.

10. The laser interferometer according to claim 1, wherein the optical path length of the first optical path and the optical path length of the second optical path are the same as each other.

11. A method for adjusting the optical axis of a laser interferometer, The aforementioned laser interferometer is A laser light source that emits laser light, A first light splitter that splits the aforementioned laser light into a first light and a second light, A light modulator that modulates the frequency of the first light and generates a reference light, A first light-receiving element that receives object light generated when the reference light and the second light are irradiated onto an object, and outputs a light-receiving signal based on the light-receiving intensity, A second optical splitter is positioned on the optical path connecting the laser light source and the first optical splitter, and guides the return light of the reference light and the return light of the object light generated in the first optical splitter to a second optical path different from the first optical path toward the laser light source. A second light-receiving element is arranged in the second optical path and acquires the respective light-receiving positions for the reflected light of the reference light and the reflected light of the object light, Equipped with, The steps include: moving the light-receiving position of the reflected light of the object back to the starting point by performing a modification operation that changes the relative relationship between the laser interferometer and the object based on the light-receiving position acquired by the second light-receiving element; The steps include: performing a scan operation that continuously changes the relative relationship from the starting point, and acquiring the AC level due to the interference between the reference light and the object light included in the received light signal; The steps include: terminating the scan operation when the acquired AC level satisfies predetermined conditions; A method for adjusting the optical axis of a laser interferometer, characterized by having the following features.

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