JP2016170160A - Laser interferometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laser interferometer that permits size reduction of optical elements while reducing noise light components.SOLUTION: In a laser interferometer, a light source unit 12 emits laser beams that permit interference. A first splitter 14 splits the laser beams into a first component and a second component. A second splitter 20 splits the first component into a main polarized beam component and a noise beam component. A third splitter 18 causes the second component and the main polarized beam component reflected by a measuring face 22 to interfere with each other. A light receiving unit 124 receives the second component under interference by the third splitter 18 and the main polarized beam component. The noise beam component of the first component is not brought to incidence on the third splitter 18.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a laser interferometer for measuring the displacement of a measurement surface.

  Patent Document 1 discloses a heterodyne interference type position detection device that separates a light beam emitted from a light source by a polarization beam splitter and does not include a noise light component that is polarized in an orthogonal direction to each separated light beam. The

  The position detection device disclosed in Patent Literature 1 separates a laser beam emitted from a light source into a P-polarized light beam and an S-polarized light beam, and a P-polarized light beam into a main polarized light component and a noise light component. And a polarization beam splitter that separates the S-polarized light beam into a main polarization component and a noise light component.

Japanese Patent Laid-Open No. 10-122816

  By the way, in the laser interferometer that splits the laser light emitted from one light source to remove noise light and interferes with the split laser light, it is detected that the ratio of noise light is reduced because the amount of light decreases. Desirable to increase accuracy. In addition, in-vehicle laser interferometers are desirably downsized because the assembly space is limited.

  The present invention has been made in view of such problems, and an object thereof is to provide a laser interferometer that can be reduced in size while reducing noise light components.

  In order to solve the above-described problem, a laser interferometer according to an aspect of the present invention includes a light source unit that emits coherent laser light, a first splitter that divides the laser light into a first component and a second component. A second splitter that divides the first component into a main polarization component and a noise light component, an interference unit that causes the second component and the main polarization component reflected by the measurement surface to interfere with each other, and a second interference caused by the interference unit And a light receiving unit that receives the component and the main polarization component. The noise light component of the first component is not incident on the interference part.

  According to this aspect, the noise light component of the first component is removed by the second splitter, and the first component and the second component are caused to interfere by the interference unit, and division and interference are realized by separate optical elements. As a result, it is possible to realize a configuration in which the noise light component of the first component does not enter the light receiving unit, and it is possible to suppress a decrease in detection accuracy due to noise. By removing the noise light component of the first component, interference between the noise light components can be suppressed in the interference unit, and for example, the second component is configured not to be incident on the optical element that removes the noise, thereby causing laser interference. The total size can be reduced.

  In the laser interferometer, the second component is not divided into a main polarization component and a noise light component. This eliminates the need for an optical element that removes the noise light component in the optical path of the second component, thereby reducing the number of parts of the laser interferometer.

  At least a part of the first component optical path may be formed by the first optical fiber, and at least a part of the second component optical path may be formed by the second optical fiber. By configuring a part of the optical path with an optical fiber, the degree of freedom of arrangement of the laser interferometer can be increased.

  The light source unit, the first splitter, the second splitter, the interference unit, and the light receiving unit are arranged separately in a main body unit, a main body unit, and a separate head, and the main body unit includes the first optical fiber and the second optical fiber. The head may be connected to the output side of the first optical fiber and the second optical fiber. The optical fiber allows the head to be freely routed and further increases the degree of freedom in the arrangement of the laser interferometer.

  The light receiving unit may be located on the emission side of the first optical fiber and the second optical fiber. By arranging the light receiving part on the emission side, the laser light emitted from the first optical fiber and the second optical fiber can be measured without returning to the main body part through the optical fiber again.

  The interference unit may change the polarization state of one of the second component and the main polarization component. With the polarizing plate, laser beams having different polarization states can be caused to interfere with one optical element.

  The displacement of the measurement surface may be derived based on the number of interference fringes of the interference light measured by the light receiving unit. Since the displacement can be detected by measuring the number of interference fringes reflected on the screen, the laser interferometer can be measured with a simple configuration.

  You may provide the frequency modulation part which gives a difference in the frequency of a 1st component and a 2nd component. The light receiving unit is a photodiode, and the displacement of the measurement surface may be derived based on a change in frequency or phase of a signal detected by the light receiving unit. By providing a difference between the frequency of the first component and the frequency of the second component, the difference can be detected as an electric signal, so that high detection accuracy can be realized.

  The frequency modulation unit may be configured by an acousto-optic element provided in each of the first component optical path and the second component optical path. By providing an acoustooptic element in each optical path, the difference between the frequency of the first component and the frequency of the second component can be reduced, and the load of the displacement calculation process based on the difference can be reduced.

  The light source unit may be a gas laser that emits single-frequency laser light. By using a gas laser, laser light having a stable frequency and wavelength can be obtained.

  The measurement surface may be configured by a corner cube prism. By using the corner cube prism, the direction of the reflected optical axis can be easily adjusted.

  According to the present invention, it is possible to provide a laser interferometer that can be reduced in size while reducing noise light components.

It is a figure for demonstrating the structure of the laser interferometer of an Example. It is a figure for demonstrating the structure of the laser interferometer of a comparison technique. It is a figure for demonstrating the structure of the laser interferometer of a 1st modification. It is a figure for demonstrating the structure of the laser interferometer of a 2nd modification. It is a figure for demonstrating the structure of the laser interferometer of a 3rd modification. It is a figure for demonstrating the structure of the laser interferometer of a 4th modification. It is a figure for demonstrating the structure of the laser interferometer of a 5th modification. It is a figure for demonstrating the structure of the laser interferometer of a 6th modification. It is a figure for demonstrating the structure of the laser interferometer of a 7th modification. It is a figure for demonstrating the structure of the laser interferometer of an 8th modification. It is a figure for demonstrating the structure of the laser interferometer of a 9th modification. It is a figure for demonstrating the structure of the laser interferometer of a 10th modification.

  FIG. 1 is a diagram for explaining the configuration of a laser interferometer 600 according to the embodiment. The laser interferometer 600 is used to detect the displacement of the measurement surface. When the measurement surface moves in the optical axis direction, the laser interferometer 600 changes the state of the interference light because the optical path length between the measurement surface and the measurement surface changes, and detects this change as a change in the frequency or phase of the electrical signal. The displacement of the measurement surface is detected.

  Laser interferometer 600 is provided in a vehicle, and uses a predetermined part of the vehicle body as a measurement surface to detect displacement of the measurement surface. A corner cube prism is attached to a predetermined part of the vehicle body as a measurement surface, and a laser interferometer 600 is provided so that laser light is incident on the corner cube prism, thereby detecting the displacement of the corner cube prism. The corner cube prism may be attached to various places as a measurement surface. For example, the laser interferometer 600 can detect the depression of the body panel by attaching the corner cube prism to the body panel.

  An arithmetic device (not shown) is connected to the laser interferometer 600, receives the detection result of the laser interferometer 600, and calculates the displacement of the measurement surface based on the detection result.

  The laser interferometer 600 includes a light source unit 12, a first splitter 14, a mirror 16, a second splitter 20, a third splitter 18, a quarter wavelength plate 26, a first acoustooptic element 28a, a second acoustooptic element 28b, and a light receiving element. Part 124.

  The light source unit 12 emits laser light having a coherent first component and second component to the first splitter 14. The laser light emitted from the light source unit 12 is composed of a P-polarized component and an S-polarized component. The light source unit 12 emits a laser beam having a single frequency, and a laser beam having a stable frequency and wavelength can be obtained by using a gas laser such as a helium neon laser.

  The first splitter 14 is a polarization beam splitter that divides the laser light, transmits the P-polarized component, and reflects the S-polarized component in the orthogonal direction. The first splitter 14 divides the laser light emitted from the light source unit 12 into two components, and emits a first component that is mainly P-polarized light and a second component that is mainly S-polarized light. The first component functions as measurement light, and the second component functions as reference light. The second component of S-polarized light reflected in the orthogonal direction from the first splitter 14 enters the third splitter 18 via the second acoustooptic device 28b.

  Here, there is a possibility that the first component and the second component of the laser light divided by the first splitter 14 may not be completely divided into the P-polarized light component and the S-polarized light component due to the manufacturing error of the first splitter 14. One component may be mixed with an S-polarized component, and the second component may be mixed with a P-polarized component. The S-polarized component contained in the first component is a noise light component with respect to the P-polarized main polarized component. The P-polarized component included in the second component is a noise light component with respect to the S-polarized main polarized component.

  The first component transmitted in the straight direction from the first splitter 14 is reflected in the orthogonal direction by the mirror 16 and is incident on the second splitter 20 via the first acoustooptic device 28a. The first acoustooptic element 28 a is provided in the optical path between the mirror 16 and the second splitter 20, and the second acoustooptic element 28 b is provided in the optical path between the first splitter 14 and the third splitter 18.

  The first acoustooptic element 28a and the second acoustooptic element 28b are AOMs (Acousto-Optic Modulators), and change the frequency of the incident polarization component by a predetermined first frequency and a predetermined second frequency, respectively. It functions as a frequency modulation unit that adjusts the frequency of the first component and the frequency of the second component by giving a difference between the frequencies of the first component and the second component. By providing a difference between the frequency of the first component and the frequency of the second component, the difference can be detected as an electrical signal, and high detection accuracy can be realized. Also, by providing an acoustooptic element in each optical path, the difference between the frequency of the first component and the frequency of the second component can be reduced, and the load of displacement calculation processing based on the difference can be reduced.

  The second splitter 20 is a polarization beam splitter that divides the first component of the laser light into a P-polarized component and an S-polarized component, reflects the noise light component of the S-polarized component, and is the main polarized light of the P-polarized component. By transmitting the component, it is divided into a main polarization component and a noise light component.

  The noise light component reflected in the orthogonal direction from the second splitter 20 is emitted in a direction different from the third splitter 18 and the light receiving unit 124 side, and does not enter the third splitter 18 and the light receiving unit 124. The noise light component is emitted to the outside from, for example, a through hole formed in the outer wall of the case. By reflecting the noise light component toward the outside and preventing the reflected noise light component from going straight ahead, the noise light component interferes and is not detected by the light receiving unit 124. . Thereby, when a noise light component is included in the first component divided by the first splitter 14, the second splitter 20 can remove the noise light component included in the first component. The second splitter 20 functions as a dividing unit that divides the first component into the main polarization component and the noise light component. By using the polarization beam splitter for the second splitter 20, the noise light component can be removed by one element. it can.

  The main polarization component transmitted in the straight direction from the second splitter 20 is incident on the quarter-wave plate 26. The quarter-wave plate 26 gives a phase difference of λ / 4 in the electric field oscillation direction of the main polarization component, and changes the main polarization component that is linearly polarized light into a circularly polarized state. The main polarization component that has become circularly polarized light is reflected by the measurement surface 22 and enters the quarter-wave plate 26. For example, the measurement surface 22 is configured by a corner cube prism, and is disposed at a predetermined portion of a vehicle to be measured. By using the corner cube prism, it is possible to easily adjust the direction of the optical axis reflected on the quarter-wave plate 26 during installation.

  The quarter-wave plate 26 gives a phase difference of λ / 4 in the electric field oscillation direction of the main polarization component, and changes the main polarization component, which is circularly polarized light, to an S-polarized state. The main polarization component of S-polarized light is incident on the second splitter 20 again. Unnecessary return reflection can be removed by the quarter-wave plate 26. The quarter-wave plate 26 functions as a polarization state variable unit that changes the polarization state of the first component so as to match the polarization states of the first component and the second component. In addition, although the aspect which changes the polarization state of a 1st component was shown, you may change so that the polarization state of a 2nd component may be united with a 1st component in a modification.

  The first component passing through the measurement surface 22 is reflected by the second splitter 20 and enters the third splitter 18. While the first splitter 14 and the second splitter 20 are polarization beam splitters, the third splitter 18 is a non-polarization beam splitter, and transmits the first component of S-polarized light at a predetermined division ratio, and the first splitter of S-polarized light. Two components are reflected at a predetermined division ratio. The third splitter 18 functions as an interference unit that interferes two incident polarized components. The third splitter 18 causes the main polarization component of the first component, which is S-polarized light, and the second component to interfere with each other and enter the light receiving unit 124. The light receiving unit 124 is, for example, a photodiode that receives interference light, and can detect displacement based on the amount of change in the frequency or phase of the electrical signal, thereby improving the detection accuracy of the displacement.

  FIG. 2 is a diagram for explaining a configuration of a laser interferometer 700 of a comparative technique. Here, the same or equivalent components and members shown in the drawings are denoted by the same reference numerals, and repeated description thereof is omitted as appropriate.

  A laser interferometer 700 shown in FIG. 2 is a technique to be compared with the laser interferometer 600 of the embodiment. The laser interferometer 700 includes a light source unit 12, a first splitter 14, a mirror 16, a first acoustooptic element 28a, a second acoustooptic element 28b, a second splitter 720, another mirror 717, a half-wave plate 719, a polarization. A splitter 721, a diffraction grating 723, and a light receiving unit 124 are provided.

  In the laser interferometer 700 shown in FIG. 2, the first component including the noise light component is reflected by the mirror 16 and is incident on the second splitter 720 via the first acousto-optic element 28a, and the second component including the noise light component. Is reflected by another mirror 717 via the second acoustooptic device 28 b and is incident on the second splitter 720. Both the primary polarization component of the first component and the primary polarization component of the second component are incident on the polarization splitter 721 via the half-wave plate 719, only the P-polarized light is transmitted by the polarization splitter 721, and is interfered by the diffraction grating 723. Incident on the light receiving unit 124.

  Compared with the laser interferometer 600 shown in FIG. 1, the laser interferometer 700 of the comparative technique shown in FIG. 2 is common in that noise light is removed using the second splitter 720. The difference is that the noise light of both the first component and the second component is removed. For this reason, in the laser interferometer 700 of the comparative technique, the second splitter 720 becomes large. The laser interferometer 600 according to the embodiment has a configuration in which the second component is not divided into a main polarization component and a noise light component. This eliminates the need for an optical element that removes the noise light component with respect to the optical path of the second component, so that the number of parts of the laser interferometer 600 can be reduced.

  In the laser interferometer 600 shown in FIG. 1, the second noise light component is also incident on the third splitter 18. Here, the main polarization component of the first component and the main polarization component of the second component are S-polarized light and interfere with each other by the third splitter 18, but the noise light component of the second component is aligned with the S-polarized light. There is no interference. In addition, when the main polarization component of the second component is reflected by the third splitter 18, even if the direction of the polarization slightly changes and interferes with the noise light component of the second component, the beat frequency is the same. The frequency will be the same and it will not be noise. In this way, the first component noise light component is removed by the second splitter 20 and the second component noise light component is not removed, so that the polarization beam splitter is not provided in the second component optical path. As compared with the laser interferometer 700 shown in FIG. 2, it is possible to reduce the influence of noise and suppress a decrease in detection accuracy while suppressing an increase in optical elements.

  In the laser interferometer 600 shown in FIG. 1, the first component of the laser light passes through the second splitter 20, is reflected by the measurement surface 22, and is incident on the second splitter 20 again. In the laser interferometer 600 that divides and measures one light source in an in-vehicle environment, it is preferable to improve the signal-to-noise ratio because the light intensity is reduced by the division and the signal intensity is weakened. In the laser interferometer 600, by causing the first component to enter the second splitter 20 twice, the reduction rate of the noise light component of the first component can be raised to a power and the signal-to-noise ratio can be improved.

  In the laser interferometer 600 shown in FIG. 1, since the laser beam incident on the second splitter 20 is only the first component, the second splitter 20 is smaller than the case where the first component and the second component are incident. Can be made lighter and lighter. For example, when the second splitter 20 is incorporated in a case as a head and can be handled, the head can be reduced in size. Making the head smaller and lighter is useful in an in-vehicle environment that is narrow and susceptible to vibration.

  FIG. 3 is a diagram for explaining a configuration of a laser interferometer 800 according to the first modification. The laser interferometer 800 includes a light source unit 12, a first splitter 14, a mirror 16, a first acoustooptic element 28a, a second acoustooptic element 28b, a second splitter 820, a third splitter 836, a quarter wavelength plate 26, and a measurement. A surface 22, a quarter-wave plate 838, a reference surface 840, a polarizing plate 842, and a light receiving unit 124.

  In the laser interferometer 800 of the first modification, the first component is incident on the second splitter 820, and the second component is reflected by another mirror 817 and incident on the second splitter 820. The noise light component of the first component is reflected by the second splitter 820, the noise light component of the second component is transmitted through the second splitter 820, and is emitted in a direction different from the third splitter 836 and the light receiving unit 124 side, The light does not enter the third splitter 836 and the light receiving unit 124. Thereby, the influence of noise can be reduced and the reduction in detection accuracy can be suppressed.

  The main polarization component of the first component is transmitted through the second splitter 820 and incident on the third splitter 836, and the main polarization component of the second component is reflected on the second splitter 820 and incident on the third splitter 836. Dividing in different directions by the splitter 836.

  The main polarization component of the first component passes through the third splitter 836 and enters the quarter-wave plate 838. The quarter-wave plate 838 changes the main polarization component that is linearly polarized light into a circularly polarized state. The main polarized light component that has become circularly polarized light is reflected by the reference surface 840 and is incident again on the quarter-wave plate 838 to change the main polarized light component that is circularly polarized light to the state of S polarized light that is linearly polarized light. The main polarization component of the first component is incident again on the third splitter 836, is reflected because it is S-polarized light, and is incident on the polarizing plate 842.

  The main polarization component of the second component is reflected by the third splitter 836 and is incident on the quarter-wave plate 26. The quarter-wave plate 26 changes the main polarization component that is linearly polarized light into a circularly polarized state. The main polarization component that has become circularly polarized light is reflected by the measurement surface 22 and is incident on the quarter-wave plate 26 again, and the main polarization component that is circularly polarized light is changed to a state of P-polarized light that is linearly polarized light. The main polarization component of the second component is incident again on the third splitter 836 and is transmitted through the polarizer 842 because it is P-polarized light.

  The main polarization component of the first component that is S-polarized light and the main polarization component of the second component that is P-polarized light are incident on the polarizing plate 842, interfere with each other at the polarizing plate 842, and are received by the light receiving unit 124. The The polarizing plate 842 functions as an interference unit that causes interference between the main polarization component of the second component and the main polarization component of the first component reflected by the measurement surface 22. The polarizing plate 842 serving as an interference unit causes interference by changing the polarization state of one of the first component main polarization component and the second component main polarization component. With the polarizing plate 842, laser beams having different polarization states can be interfered by one optical element.

  According to the laser interferometer 800 of the first modified example, although the noise light component is removed by the second splitter 820, the loss of the amount of light incident on the light receiving unit 124 can be suppressed as compared with the case of causing interference by the non-polarizing splitter. . Further, when an optical fiber for combining the first component and the second component is used in the optical path from the second splitter 820 to the third splitter 836, it can be configured by one.

  FIG. 4 is a diagram for explaining the configuration of a laser interferometer 900 according to the second modification. Compared with the laser interferometer 800 shown in FIG. 3, the laser interferometer 900 shown in FIG. 4 does not use a ¼ wavelength plate in the optical path of the reference light, and the number of laser beams incident on the third splitter 936 is small. Therefore, the number of components can be reduced and the optical element can be downsized.

  The laser interferometer 900 includes a light source unit 12, a first splitter 14, a mirror 16, a first acoustooptic element 28a, a second acoustooptic element 28b, another mirror 817, a second splitter 820, a third splitter 936, and a quarter. A wave plate 26, a measurement surface 22, a reflection part 944, a diffraction grating 946 and a light receiving part 124 are provided.

  The second component, which is the reference light, is reflected by the second splitter 820, is reflected by the reflecting portion 944, and enters the diffraction grating 946. The reflection unit 944 may be configured with a mirror or a corner cube prism.

  The first component, which is measurement light, passes through the second splitter 820, passes through the third splitter 936, and enters the quarter-wave plate 26. The third splitter 936 can remove a slight noise light component included in the first component.

  The main polarization component of the first component is incident on the quarter-wave plate 26 and is changed to a circularly polarized state. The main polarized light component that has become circularly polarized light is reflected by the measurement surface 22 and is incident again on the quarter-wave plate 26 to change the main polarized light component that is circularly polarized light into the state of S polarized light that is linearly polarized light. The main polarization component of the first component is incident again on the third splitter 936 and is reflected and incident on the diffraction grating 946 because it is S-polarized light.

  The main polarization component of the first component and the main polarization component of the second component are both S-polarized light, and are interfered by the diffraction grating 946 and received by the light receiving unit 124. According to the laser interferometer 900 of the second modified example, the first component passes through the second splitter 820 once and the third splitter 936 twice, so that the reduction rate of the noise light component of the first component is raised to a power. Can be increased. The second component has a smaller number of passes through the polarization splitter than the first component, but the noise light component of the second component does not interfere with the main polarization component of the first component. An increase in the size of the interferometer 900 can be suppressed.

  FIG. 5 is a diagram for explaining the configuration of a laser interferometer 1000 according to the third modification. Compared with the laser interferometer 600 shown in FIG. 1, the laser interferometer 1000 shown in FIG. 5 forms at least a part of the first component optical path with the first optical fiber 30a, and at least a part of the second component optical path. Are different in that they are formed by the second optical fiber 30b. With the optical fiber, the degree of freedom of arrangement of the laser interferometer 1000 can be increased.

  The first optical fiber 30 a is provided between the first acoustooptic element 28 a and the second splitter 20, and the second optical fiber 30 b is provided between the second acoustooptic element 28 b and the third splitter 18.

  The light source unit 12, the first splitter 14, the mirror 16, the first acoustooptic element 28 a and the second acoustooptic element 28 b constitute the main body unit 13. The second splitter 20, the quarter wavelength plate 26, the third splitter 18 and the light receiving unit 124 constitute a head 1011 and are integrated with the case. In addition, you may comprise a main-body part and a head not only in the components structure of the main-body part 13 and the head 1011 which are shown in FIG.

  The main body 13 is connected to the incident side of the first optical fiber 30a and the second optical fiber 30b, and the head 1011 is connected to the output side of the first optical fiber 30a and the second optical fiber 30b. Thereby, the freedom degree of arrangement | positioning of the head 1011 can be raised.

  The light receiving unit 124 is located on the emission side of the first optical fiber 30 a and the second optical fiber 30 b and is accommodated in the head 1011. By arranging the light receiving part 124 on the emission side, the laser light emitted from the first optical fiber 30a and the second optical fiber 30b can be measured without returning to the main body part 13 through the optical fiber again.

  FIG. 6 is a diagram for explaining the configuration of a laser interferometer 1100 according to the fourth modification. In the laser interferometer 1100 shown in FIG. 6, in the optical path of the first component and the second component, measurement is performed after passing through the polarization splitter and the quarter wavelength plate after the first acoustooptic element 28a and the second acoustooptic element 28b. It is configured to be incident on the surface 22 or the reference surface 840.

  The laser interferometer 1100 includes a light source unit 12, a first splitter 14, a mirror 16, a first acoustooptic element 28a, a second acoustooptic element 28b, a second splitter 20, a quarter wavelength plate 26, a measurement surface 22, and a fourth. A splitter 1150, a quarter-wave plate 838, a reference surface 840, a mirror 1152, a third splitter 1154, a polarizing plate 842, and a light receiving unit 124 are provided.

  The second component, which is the reference light, exits from the second acoustooptic device 28 b and enters the fourth splitter 1150, the main polarization component is reflected by the fourth splitter 1150, and the noise light component passes through the fourth splitter 1150. . The main polarization component of the second component is incident on the quarter-wave plate 838, changed to a circularly polarized state, reflected on the reference surface 840, and incident on the quarter-wave plate 838 again, and is circularly polarized. The main polarization component is changed to a state of P polarization, which is linear polarization, and enters the fourth splitter 1150. The main polarization component of P-polarized light is transmitted through the fourth splitter 1150, reflected by the mirror 1152, and incident on the third splitter 1154.

  The first component, which is the measurement light, is emitted from the first acoustooptic device 28a, then enters the measurement surface 22 via the second splitter 20 and the quarter-wave plate 26, is reflected, and is again a quarter wavelength. The light enters the third splitter 1154 via the plate 26 and the second splitter 20.

  The main polarization component of the first component is transmitted through the third splitter 1154, and the main polarization component of the second component is reflected by the third splitter 1154 and is incident on the polarizing plate 842 together. The main polarization component of the first component and the main polarization component of the second component enter the polarizing plate 842, interfere with the polarizing plate 842, and are received by the light receiving unit 124.

  According to the laser interferometer 1100 of the sixth modification, it is possible to suppress an increase in size of the polarization splitter by providing the optical paths of the first component and the second component independently and not using the polarization splitter in common.

  FIG. 7 is a diagram for explaining a configuration of a laser interferometer 10 according to a fifth modification. The laser interferometer 10 is used to detect the displacement of the measurement surface. When the measurement surface moves in the direction of the optical axis, the optical path length between the measurement surface changes, so the state of the interference light changes, and the displacement of the measurement surface is detected by counting this change as the number of interference fringes. The

  The laser interferometer 10 is provided in a vehicle and detects a displacement of the measurement surface with a predetermined part of the vehicle body as a measurement surface. A corner cube prism is attached to a predetermined part of the vehicle body as a measurement surface, and a laser interferometer 10 is provided so that laser light is incident on the corner cube prism, thereby detecting the displacement of the corner cube prism. The corner cube prism may be attached to various places as a measurement surface. For example, the laser interferometer 10 can detect the depression of the body panel by attaching the corner cube prism to the body panel.

  An arithmetic device (not shown) is connected to the laser interferometer 10, receives the detection result of the laser interferometer 10, and calculates the displacement of the measurement surface based on the detection result.

  The laser interferometer 10 includes a light source unit 12, a first splitter 14, a mirror 16, a second splitter 20, a third splitter 18, a quarter wavelength plate 26, and a light receiving unit 24. The light source unit 12, the first splitter 14, the mirror 16, the third splitter 18, the second splitter 20, and the quarter wavelength plate 26 are housed in the case as the head 11 and are provided integrally.

  The light source unit 12 emits laser light having a coherent first component and second component to the first splitter 14. The laser light emitted from the light source unit 12 is composed of a P-polarized component and an S-polarized component. The light source unit 12 can obtain laser light having a stable wavelength by using, for example, a helium neon laser.

  The first splitter 14 is a polarization beam splitter that divides the laser light, transmits the P-polarized component, and reflects the S-polarized component in the orthogonal direction. The first splitter 14 divides the laser light emitted from the light source unit 12 into two components, and emits a first component that is mainly P-polarized light and a second component that is mainly S-polarized light. The first component functions as measurement light, and the second component functions as reference light. The second component of S-polarized light reflected from the first splitter 14 in the orthogonal direction is incident on the third splitter 18.

  Here, there is a possibility that the first component and the second component of the laser light divided by the first splitter 14 may not be completely divided into the P-polarized light component and the S-polarized light component due to the manufacturing error of the first splitter 14. One component may be mixed with an S-polarized component, and the second component may be mixed with a P-polarized component. The component of S polarization included in the first component is a noise light component for P polarization.

  The first component transmitted in the straight direction from the first splitter 14 is reflected by the mirror 16 in the orthogonal direction and is incident on the second splitter 20. The second splitter 20 is a polarization beam splitter that divides the first component of the laser light into a P-polarized component and an S-polarized component, reflects the noise light component of the S-polarized component, and is the main polarized light of the P-polarized component. Permeates the ingredients.

  The noise light component reflected in the orthogonal direction from the second splitter 20 is emitted in a direction different from the third splitter 18 and the light receiving unit 24 side, and does not enter the third splitter 18 and the light receiving unit 24. The noise light component is emitted to the outside through a through hole formed in the outer wall of the head 11. The noise light component is reflected to the outside, and the reflection is not placed before the reflected noise light component goes straight, so that the noise light component interferes and is not detected by the light receiving unit 24. . Thereby, when a noise light component is included in the first component divided by the first splitter 14, the noise light component included in the first component can be removed.

  The main polarization component transmitted in the straight direction from the second splitter 20 is incident on the quarter-wave plate 26. The quarter-wave plate 26 gives a phase difference of λ / 4 in the electric field oscillation direction of the main polarization component, and changes the main polarization component that is linearly polarized light into a circularly polarized state. The main polarization component that has become circularly polarized light is reflected by the measurement surface 22 and enters the quarter-wave plate 26. For example, the measurement surface 22 is configured by a corner cube prism, and is disposed at a predetermined portion of a vehicle to be measured.

  The quarter-wave plate 26 gives a phase difference of λ / 4 in the electric field oscillation direction of the main polarization component, and changes the main polarization component, which is circularly polarized light, to an S-polarized state. The main polarization component of S-polarized light is incident on the second splitter 20 again. Unnecessary return reflection can be removed by the quarter-wave plate 26. The quarter-wave plate 26 functions as a polarization state variable unit that changes the polarization state of the first component so as to match the polarization states of the first component and the second component.

  The first component passing through the measurement surface 22 is reflected by the second splitter 20 and enters the third splitter 18. While the first splitter 14 and the second splitter 20 are polarization beam splitters, the third splitter 18 is a non-polarization beam splitter, and transmits the first component of S-polarized light at a predetermined division ratio, and the first splitter of S-polarized light. Two components are reflected at a predetermined division ratio. The third splitter 18 functions as an interference unit that interferes two incident polarized components. The third splitter 18 causes the first main polarization component and the second component, which are S-polarized light, to interfere with each other and enter the light receiving unit 24. By using a non-polarizing beam splitter as the interference unit, it is possible to suppress a decrease in the amount of light.

  The light receiving unit 24 is a screen and projects the interference light composed of the first main polarization component and the second component. Interference fringes are projected on the light receiving unit 24 by the interference light, and the displacement of the measurement surface 22 can be detected based on the number of interference fringes. Accordingly, since the displacement can be detected by measuring the number of interference fringes reflected on the screen, the laser interferometer 10 can be measured with a simple configuration. By dividing the noise light component of the laser light by the second splitter 20 and causing the two laser lights to interfere with each other by the third splitter 18, the division and interference are realized by different optical elements, and the noise light component is received by the light receiving unit. Therefore, it is possible to prevent the detection accuracy from being lowered due to noise. Further, the noise light component of the measurement light is removed, and the noise light components are not interfered by the third splitter 18, that is, the third splitter 18 is configured so that the P-polarized noise light components do not interfere with each other. The laser interferometer 10 can be reduced in size as compared with the case where the noise light components of both the measurement light and the reference light are removed. Further, by removing noise from only one of the components divided by the first splitter 14, the head 11 of the laser interferometer 10 is not enlarged compared to the case of removing both noise light components. Noise due to interference can be suppressed. Compared with the case where the noise of the first component and the noise of the second component are removed by one polarization beam splitter, the second splitter 20 removes only the noise of the first component, so that the size can be reduced.

  FIG. 8 is a diagram for explaining the configuration of a laser interferometer 100 according to a sixth modification. Here, the same or equivalent components and members shown in the drawings are denoted by the same reference numerals, and repeated description thereof is omitted as appropriate.

  The laser interferometer 100 of the sixth modified example is a heterodyne system, and the frequency of the first component that is the measurement light is different from the frequency of the second component that is the reference light. Is detected. By causing laser beams having different frequencies to interfere with each other, a beat is generated. By measuring the phase of the beat, a phase difference between the reference light and the beat of the measurement light is electrically detected, and a change in the optical path difference on the measurement surface 22 is detected. Measure. The light receiving unit 124 is, for example, a photodiode that receives interference light, and is provided in the head 111. Since the heterodyne laser interferometer 100 can detect displacement from an electric signal, the displacement can be detected with high accuracy.

  Further, the laser interferometer 100 of the sixth modification is different from the laser interferometer 10 shown in FIG. 7 in that an acousto-optic element is provided in the optical path. The first acoustooptic element 28a and the second acoustooptic element 28b are AOMs (Acousto-Optic Modulators) that change the frequency of the incident polarization component by a predetermined frequency, and the frequencies of the first component and the second component. Set. The first acoustooptic element 28 a is provided in the optical path between the mirror 16 and the second splitter 120, and the second acoustooptic element 28 b is provided in the optical path between the first splitter 114 and the third splitter 18.

  FIG. 9 is a diagram for explaining the configuration of a laser interferometer 200 according to a seventh modification. The laser interferometer 200 of the second modified example uses optical fibers for the optical paths of the first component that is measurement light and the second component that is reference light, as compared with the laser interferometer 100 of the sixth modified example. It is different.

  The first optical fiber 30 a is provided between the first acoustooptic element 28 a and the second splitter 120, and the second optical fiber 30 b is provided between the second acoustooptic element 28 b and the third splitter 18. By freely arranging the incident side and the emitting side of the optical fiber, the degree of freedom of arrangement of the optical elements in the head 111 is increased, and the head 111 can be miniaturized.

  FIG. 10 is a diagram for explaining the configuration of a laser interferometer 300 according to the eighth modification. Compared to the laser interferometer 200 of the seventh modification, the laser interferometer 300 of the eighth modification is provided with a branching fiber coupler in the optical fibers of the measurement light and the reference light, and the laser light branched from the fiber coupler. Is used to detect the displacement of another measurement surface 322. Thereby, two-point multipoint measurement can be performed.

  The first optical fiber 30a and the first fiber coupler 32a constitute a 2 × 1 fiber coupler, and the measurement light incident on the first optical fiber 30a is branched into two to be emitted. The second optical fiber 30b and the second fiber coupler 32b constitute a 2 × 1 fiber coupler, and the measurement light incident on the second optical fiber 30b is branched into two and emitted.

  The optical path of each laser beam after being emitted from the first optical fiber 30a and the second optical fiber 30b is the same as the optical path of each laser beam after being emitted from the first fiber coupler 32a and the second fiber coupler 32b. is there.

  The first component that is the measurement light emitted from the first fiber coupler 32 a enters the fourth splitter 320. The second component emitted from the second fiber coupler 32 b enters the fifth splitter 318.

  The fourth splitter 320 is a polarization beam splitter that separates the polarization components of the laser light. The fourth splitter 320 divides the first component into a main polarization component and a noise light component. The main polarization component transmitted in the straight direction from the fourth splitter 320 is converted into circularly polarized light by the wave plate 326, irradiated to the measurement surface 322 different from the measurement surface 22, and reflected by 180 degrees on the measurement surface 322. Then, the light is changed into linearly polarized light by the wave plate 326 and is incident on the fourth splitter 320. The measurement surface 322 may be the same measurement target as the measurement surface 22.

  The noise light component reflected in the orthogonal direction from the fourth splitter 320 is reflected in a direction not entering the light receiving unit 24 and the light receiving unit 324. The main polarization component that is incident again on the fourth splitter 320 from the measurement surface 322 is reflected by the fourth splitter 320 and incident on the fifth splitter 318. The fifth splitter 318 is a non-polarizing beam splitter similar to the third splitter 18, and functions as an interference unit that causes the two polarized components to enter.

  The fifth splitter 318 reflects a part of the second component to the light receiving unit 324, transmits a part of the main polarization component of the first component via the measurement surface 322, and enters the light receiving unit 324. The fifth splitter 318 causes the main polarization component of the first component and the second component to interfere with each other and enter the light receiving unit 324. The light receiving unit 324 is a photodiode similarly to the light receiving unit 24. In this way, the light receiving unit 24 and the light receiving unit 324 can measure at two points.

  FIG. 11 is a diagram for explaining the configuration of a laser interferometer 400 according to a ninth modification. Compared with the laser interferometer 100 of the sixth modified example, the laser interferometer 400 of the ninth modified example has a configuration in which the light source unit 512 emits only P-polarized laser light, and the P-polarized reference light has a half wavelength. The configuration for changing to S-polarized light differs depending on the plate 34.

  The first splitter 414 is a non-polarizing beam splitter, and divides the P-polarized laser light emitted from the light source unit 512 into a first component and a second component. The first component is incident on the second splitter 20 via the mirror 16 and the first acousto-optic element 28a, is reflected on the measurement surface 22 via the quarter-wave plate 26, and is incident on the second splitter 20 again. Is done. Further, the first component is incident on the third splitter 18, is transmitted at a predetermined division ratio, and enters the light receiving unit 124.

  The second component of the P-polarized light reflected by the first splitter 414 is incident on the half-wave plate 34 via the second acoustooptic device 28b. The half-wave plate 34 changes the second component from P-polarized light to S-polarized light. The second component of S-polarized light is incident on the third splitter 18, interferes with the first component of S-polarized light, and is received by the light receiving unit 124. The quarter-wave plate 26 and the half-wave plate 34 function as a polarization state variable unit that changes the polarization state of the first component or the second component so as to match the polarization states of the first component and the second component.

  FIG. 12 is a diagram for explaining the configuration of a laser interferometer 500 according to the tenth modification. The laser interferometer 500 is different from the laser interferometer 10 shown in FIG. 7 in that the first splitter 514 and the second splitter 520 are non-polarizing beam splitters.

  The light source unit 12 emits coherent laser light to the first splitter 14. The first splitter 514 divides the laser light emitted from the light source unit 12 into two components, and emits a coherent first component and a second component orthogonal to the first component.

  The first splitter 514 is a non-polarizing beam splitter. The first component transmitted in the straight direction from the first splitter 514 is reflected by the mirror 16 in the orthogonal direction and enters the second splitter 520. The second component reflected in the orthogonal direction from the first splitter 514 enters the third splitter 18.

  The second splitter 520 is a non-polarizing beam splitter that divides the laser light. The second splitter 20 divides the first component into a main component and a noise light component. The main component transmitted in the straight direction from the second splitter 20 is irradiated on the measurement surface 22, reflected by 180 degrees on the measurement surface 22, and incident on the second splitter 20.

  The noise light component reflected in the orthogonal direction from the second splitter 520 is emitted in a direction different from the third splitter 18 and the light receiving unit 24 side, and does not enter the third splitter 18 and the light receiving unit 24.

  The main component of the first component incident again on the second splitter 520 from the measurement surface 22 is reflected by the second splitter 520 and incident on the third splitter 18. The third splitter 18 is a non-polarizing beam splitter that divides the laser light, and functions as an interference unit that causes the components of two incident light beams to interfere with each other. The third splitter 18 causes the first component and the second component to interfere with each other and enter the light receiving unit 24.

  The present invention is not limited to the above-described embodiments and modifications, and various modifications such as design changes can be added based on the knowledge of those skilled in the art. The configuration shown in each drawing is for explaining an example, and can be appropriately changed as long as the configuration can achieve the same function.

  DESCRIPTION OF SYMBOLS 10 Laser interferometer, 11 Head, 12 Light source part, 14 1st splitter, 16 Mirror, 18 3rd splitter, 20 2nd splitter, 22 Measurement surface, 24 Light receiving part, 26 1/4 wavelength plate, 28a 1st acoustooptic Element, 28b second acoustooptic element, 30a first optical fiber, 30b second optical fiber, 32a first fiber coupler, 32b second fiber coupler, 34 1/2 wavelength plate.

Claims (11)

A light source that emits coherent laser light;
A first splitter for dividing the laser light into a first component and a second component;
A second splitter for dividing the first component into a main polarization component and a noise light component;
An interference unit that causes interference between the second component and the main polarization component reflected by the measurement surface;
A light receiving unit that receives the second component and the main polarization component interfered by the interference unit,
The laser interferometer, wherein the noise light component is not incident on the interference unit.   The laser interferometer according to claim 1, wherein the second component is not divided into a main polarization component and a noise light component. Forming at least part of the optical path of the first component with a first optical fiber;
The laser interferometer according to claim 1, wherein at least a part of the optical path of the second component is formed by a second optical fiber. The light source unit, the first splitter, the second splitter, the interference unit, and the light receiving unit are divided into a main body unit and a separate head from the main body unit,
The main body is connected to an incident side of the first optical fiber and the second optical fiber, and the head is connected to an outgoing side of the first optical fiber and the second optical fiber. 3. The laser interferometer according to 3.   5. The laser interferometer according to claim 3, wherein the light receiving unit is located on an emission side of the first optical fiber and the second optical fiber.   6. The laser interferometer according to claim 1, wherein the interference unit changes a polarization state of one of the second component and the main polarization component. 7.   The laser interferometer according to any one of claims 1 to 6, wherein the displacement of the measurement surface is derived based on the number of interference fringes of interference light measured by the light receiving unit. A frequency modulation unit for providing a difference in frequency between the first component and the second component;
The light receiving unit is a photodiode,
The laser interferometer according to claim 1, wherein the displacement of the measurement surface is derived based on a change in frequency or phase of a signal detected by the light receiving unit.   The laser interferometer according to claim 8, wherein the frequency modulation unit is configured by an acousto-optic element provided in each of the first component optical path and the second component optical path.   The laser interferometer according to claim 1, wherein the light source unit is a gas laser that emits a single-frequency laser beam.   The laser interferometer according to claim 1, wherein the measurement surface is configured by a corner cube prism.

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