JP5984555B2 - Displacement detector - Google Patents

Description

  The present invention relates to a displacement detection device that detects a displacement of a surface to be measured by a non-contact sensor using light emitted from a light source, and more particularly to a technique for detecting a displacement in a vertical direction of the surface to be measured.

  Conventionally, a displacement detection device using light has been widely used as a device for measuring the displacement and shape of a surface to be measured in a non-contact manner. As a typical example, there is a method of irradiating a surface to be measured with laser light and detecting a change in position of reflected light by PSD. However, this method has a problem in that it is easily affected by the inclination of the surface to be measured, the sensitivity is low, and the measurement resolution decreases when the measurement range is expanded.

  On the other hand, there is a method using a Michelson interferometer with the surface to be measured as a mirror. This method has a wide detection range and excellent linearity. However, when the measurement range is widened, the method receives a change in the wavelength of the light source and a change in the refractive index of the air.

  On the other hand, the light emitted from the light source is condensed on the surface to be measured by the objective lens, and the reflected light reflected by the surface to be measured is condensed by the astigmatic optical element and incident on the light receiving element, and then focused by the astigmatism method. Generate an error signal. Then, the servo mechanism is driven using the focus error signal, and the objective lens is displaced so that the focal position of the objective lens becomes the surface to be measured. At this time, there is a method of detecting the displacement of the surface to be measured by reading a scale of a linear scale that is integrally attached to the objective lens via a connecting member (for example, see Patent Document 1). This method has an advantage that it is difficult to receive a change in the inclination of the surface to be measured, and a large measurement range can be measured with high resolution.

  In the displacement detection device disclosed in Patent Document 1, in order to increase the accuracy of displacement detection, the numerical aperture (NA: Numerical Aperture) of the objective lens is increased to reduce the beam diameter focused on the surface to be measured. ing. For example, when the beam diameter formed on the surface to be measured is about 2 μm, the detection accuracy of the linear scale is about several nm to several hundred nm.

Japanese Patent Laid-Open No. 5-89480

  However, in the conventional displacement detection apparatus described in Patent Document 1, the objective lens is moved up and down in the optical axis direction by a drive mechanism such as an actuator using a magnet and a coil. Therefore, the mechanical response frequency of the vertical movement of the objective lens is limited by the structure and mass of the actuator. As a result, with the displacement detection device described in Patent Document 1, it was difficult to measure an object to be measured that vibrates at high speed. In addition, while the detection point can be narrowed down, there is a problem that a large error occurs due to the influence of a foreign object on the object to be measured and a fine shape change close to the beam shape, and the use conditions are limited. .

  An object of the present invention is to provide a displacement detection device that can detect a displacement in a height direction of a member to be measured with high accuracy and can perform stable measurement at high speed.

In order to solve the above problems and achieve the object of the present invention, a displacement detection device of the present invention includes a light source for irradiating light, a light beam splitting unit, a transmission type diffraction grating, a reflecting unit, and a light beam coupling unit. A light receiving portion, an optical path correction member, and a relative position information output means.
The light beam splitting unit splits the light emitted from the light source into a first light beam that enters the member to be measured and a second light beam that serves as reference light.
The diffraction grating diffracts the first light beam divided by the light beam dividing unit and reflected by the surface to be measured of the member to be measured, and again causes the diffracted first light beam to enter the surface to be measured of the member to be measured.
The reflecting unit reflects the second light beam divided by the light beam dividing unit.
The light beam coupling unit superimposes the first light beam diffracted by the diffraction grating and reflected again by the measurement surface with the second light beam reflected by the reflecting unit.
The light receiving unit receives the interference light of the first light beam and the second light beam superimposed by the light beam coupling unit.
The optical path correcting member is provided between the light beam coupling portion and the member to be measured, and the first light beam and the second light beam whose traveling direction is tilted and the traveling direction is inclined are substantially parallel at the light beam coupling portion. The optical path of the first light flux is corrected so as to keep it.
The relative position information output means outputs displacement information in the height direction of the surface to be measured based on the interference signal of the interference light received by the light receiving unit.

  In addition, the optical path length from the light beam splitting unit to the light beam combining unit in the first light beam and the optical path length from the light beam splitting unit to the light beam combining unit in the second light beam are set to be approximately equal.

  According to the displacement detection device of the present invention, since a conventional driving mechanism is not required, heat generated during use can be suppressed. Furthermore, since there is no need to drive the drive mechanism, the problem of response frequency can be solved and the use conditions can be widened.

  Furthermore, by providing the optical path correction member, even when the surface to be measured is inclined, the interference signal hardly changes and stable measurement can be performed.

  In addition, since the optical path length of the first light beam and the optical path length of the second light beam are set to be equal, even if there is a wavelength variation of the light source due to changes in atmospheric pressure, humidity, or temperature, the first light beam And the influence which the 2nd light beam receives can be made equal. As a result, it is not necessary to perform atmospheric pressure correction, humidity correction, and temperature correction, and stable measurement is possible.

It is a schematic block diagram which shows the structure of the 1st Embodiment of the displacement detection apparatus of this invention. It is explanatory drawing which shows the principal part concerning the 1st Example of the displacement detection apparatus of this invention. It is a block diagram which shows the relative position information output means concerning the 1st Example of the displacement detection apparatus of this invention. It is explanatory drawing which shows the state which the to-be-measured member tilted in the direction from which the position of the height direction in two irradiation spots differs. It is explanatory drawing which shows the state which the to-be-measured member tilted centering on the line substantially parallel to the line | wire which connects two irradiation spots. It is explanatory drawing shown about the effect | action of the optical path correction member in the 1st Example of the displacement detection apparatus of this invention. It is a front view which shows the aperture member in the displacement detection apparatus of this invention. It is explanatory drawing which shows the effect | action of an aperture member. It is a schematic block diagram which shows the structure of the 2nd Example of the displacement detection apparatus of this invention. It is explanatory drawing which shows the structure around the light source in the 2nd Example of the displacement detection apparatus of this invention. It is explanatory drawing which shows the structure around the light source in the 3rd Embodiment of the displacement detection apparatus of this invention. It is explanatory drawing which shows the structure around the light source in the 4th Example of the displacement detection apparatus of this invention.

Embodiments of the displacement detection device of the present invention will be described below with reference to FIGS. In addition, the same code | symbol is attached | subjected to the common member in each figure. The present invention is not limited to the following form.
Further, the various lenses described in the following description may be a single lens or a lens group.

1. First Embodiment of Displacement Detection Device First, the configuration of a first embodiment (hereinafter referred to as “this example”) of a displacement detection device of the present invention will be described with reference to FIGS.

1-1. Configuration Example of Displacement Detection Device FIG. 1 is a schematic configuration diagram showing a configuration of a displacement detection device, FIG. 2 is an explanatory diagram showing a main part of the displacement detection device, and FIG. 3 is a diagram of relative position information output means in the displacement detection device. It is a block diagram which shows schematic structure.

  The displacement detection device 1 of this example is a displacement detection device that can detect a displacement in a vertical direction on a surface to be measured using a diffraction grating. As shown in FIG. 1, the displacement detection device 1 includes a light source 2, a light beam dividing unit 3 that divides light emitted from the light source into two light beams, a diffraction grating 4, and a mirror 6 that illustrates an example of a reflecting unit. And a light receiving portion 8. Further, the displacement detection apparatus 1 includes a first convergent lens 5A, a second convergent lens 5B, a first optical path correction member 7A, a second optical path correction member 7B, a light beam coupling portion 14, and a device under measurement. Relative position information output means 10 is provided for outputting relative position information (displacement information) in the direction orthogonal to the surface to be measured of the member 9, that is, in the height direction.

  Examples of the coherent light source in the light source 2 include a laser diode, a super luminescence diode, a gas laser, a solid-state laser, and a light emitting diode.

  When a light source having a long coherence distance is used as the light source 2, the tilt tolerance is widened because the light source 2 is not easily affected by the difference in the optical path length between the object light and the reference light due to the tilt of the measurement surface of the member 9 to be measured. In addition, as the coherence distance of the light source 2 is shortened, noise due to unnecessary stray light interference can be prevented, and highly accurate measurement can be performed.

  Furthermore, when a single mode laser is used as the light source 2, it is desirable to control the temperature of the light source 2 in order to stabilize the wavelength. In addition, high-frequency superimposition or the like may be added to the light of the single mode laser to reduce the coherence of the light. Further, even when a multi-mode laser is used, by controlling the temperature of the light source 2 with a Peltier element or the like, noise due to unnecessary interference of stray light can be prevented and more stable measurement can be performed.

  The S-polarized light emitted from the light source 2 enters the light beam splitting unit 3 that is a non-polarizing beam splitter. Note that. Between the light source 2 and the light beam splitting unit 3, a lens 11 made of a collimator lens or the like is disposed. The lens 11 collimates the light emitted from the light source 2 into parallel light. Therefore, the light collimated to the parallel light by the lens 11 enters the light beam splitting unit 3.

  The light beam splitting unit 3 splits the collimated light into a first light beam L1 that is object light and a second light beam L2 that is reference light. The first light beam L1 is applied to the member 9 to be measured, and the second light beam L2 is applied to the mirror 6. Further, a first convergent lens 5A is disposed between the light beam splitting unit 3 and the member 9 to be measured, and a second convergent lens 5B is disposed between the light beam splitting unit 3 and the mirror 6.

  As shown in FIG. 1B, the first converging lens 5A and the second converging lens 5B are cylindrical lenses having a curvature in a plane formed by a first direction X and an optical axis direction Z described later. The first converging lens 5A and the second converging lens 5B can condense the first light beam L1 and the second light beam L2 only in the first direction X. The first converging lens 5A converges the first light beam L1 from the parallel light to the converging light, and the second converging lens 5B converges the second light beam L2 from the parallel light to the converging light.

  In this example, the example in which cylindrical lenses are used as the first converging lens 5A and the second converging lens 5B has been described. However, the present invention is not limited to this. The first converging lens 5A and the second converging lens 5B are not particularly limited as long as they can converge the first light beam L1 and the second light beam L2 only in a predetermined direction and convert the parallel light into convergent light.

  A polarizing plate may be provided between the light source 2 and the light beam splitting unit 3. As a result, it is possible to remove leakage light and noise that are slightly present as polarization components orthogonal to each polarization.

  Of the two light beams L1 and L2 divided by the light beam splitting unit 3, the first light beam L1 is incident on the first irradiation spot P1 on the surface to be measured of the member 9 to be measured. The member to be measured 9 reflects the first light beam L1 incident on the first irradiation spot P1 and makes it incident on the diffraction grating 4.

  Further, a mirror 6 is disposed at a position facing the member to be measured 9. The mirror 6 is irradiated with the second light beam L2 split by the light beam splitting unit 3. The second light beam L2 is incident on the reflection-side first irradiation spot S1 on the reflection surface of the mirror 6. Similar to the member 9 to be measured, the mirror 6 reflects the incident second light beam L2 and makes it incident on the diffraction grating 4.

  The diffraction grating 4 is a transmission type diffraction grating. The first light beam L1 diffracted by the diffraction grating 4 is incident on a second irradiation spot P2 different from the first irradiation spot P1 on the surface to be measured of the member 9 to be measured. In addition, the member to be measured 9 reflects the first light beam L1 diffracted by the diffraction grating 4 and incident on the second irradiation spot P2, and makes it incident on the light beam coupling unit 14 which is a polarization beam splitter. A first optical path correction member 7A and a phase plate 12 are disposed between the member to be measured 9 and the light beam coupling portion 14.

  Similarly, the second light beam L2 diffracted by the diffraction grating 4 is incident on a reflection-side second irradiation spot S2 different from the reflection-side first irradiation spot S1 on the reflection surface of the mirror 6. The mirror 6 reflects the second light beam L2 diffracted by the diffraction grating 4 and incident on the reflection-side second irradiation spot S2, and causes the light beam coupling portion 14 to enter. Further, a second optical path correction member 7B and a dummy glass 13 are disposed between the mirror 6 and the light beam coupling portion 14.

  The phase plate 12 is composed of a half-wave plate. Further, as the dummy glass 13, a glass having a refractive index close to that of the phase plate 12 is used. Further, the thickness of the dummy glass 13 is set substantially equal to the thickness of the phase plate 12. Thereby, the optical path length of the 1st light beam L1 and the optical path length of the 2nd light beam L2 can be made substantially equal.

  As shown in FIG. 1C, the first optical path correction member 7A and the second optical path correction member 7B are cylindrical lenses having a curvature only in a plane M1 formed in a first direction X and an optical axis direction Z, which will be described later. It is configured. Detailed configurations of the first optical path correction member 7A and the second optical path correction member 7B will be described later.

  The diffraction grating 4 is arranged so that it is substantially perpendicular to the surface to be measured of the member 9 to be measured, that is, the angle formed by the diffraction surface of the diffraction grating 4 and the surface to be measured of the member 9 to be measured is approximately 90 °. ing.

  The accuracy with which the diffraction grating 4 is arranged with respect to the member 9 to be measured is variously set according to the measurement accuracy required for the displacement detection device 1. That is, when high accuracy is required for the displacement detection device 1, it is preferable to arrange the diffraction grating 4 in a range of 90 ° ± 0.5 ° with respect to the surface to be measured of the member 9 to be measured. On the other hand, even when the diffraction grating is arranged in the range of 90 ° to ± 2 ° with respect to the measurement surface of the member to be measured, when the displacement detection device 1 is used for low-precision measurement of a machine tool or the like, It is enough.

Here, with reference to FIG. 2, the principal part of the displacement detection apparatus 1 of this example is demonstrated.
FIG. 2 is an explanatory diagram showing a main part of the displacement detection device 1.

  As shown in FIG. 2, the diffraction grating 4 is disposed substantially perpendicular to the member 9 to be measured. Therefore, the first light beam L1 incident on the first irradiation spot P1 of the measured member 9 at the incident angle θa is incident on the diffraction grating 4 at the incident angle π / 2−θa. Further, the first light beam L1 is incident on the second irradiation spot P2 of the measured member 9 at an incident angle θb.

The grating pitch Λ of the diffraction grating 4 is preferably set so that the diffraction angle is substantially equal to the incident angle to the diffraction grating 4. That is, as described above, the grating pitch Λ of the diffraction grating 4 satisfies the following expression 1 where θa is the first incident angle to the member 9 to be measured, θb is the second incident angle, and λ is the wavelength.
[Formula 1]
Λ = nλ / (sin (π / 2−θa) + sin (π / 2−θb))
Note that n is a positive order.

When the incident angle to the diffraction grating 4 is equal to the diffraction angle, the first irradiation spot P1 and the second irradiation spot P2 can be configured symmetrically with respect to the diffraction grating 4. And Formula 1 can be shown as the following Formula 2.
[Formula 2]
2Λsin θ = nλ
Note that θ is an incident angle and a diffraction angle to the diffraction grating 4.
That is, the Bragg condition can be satisfied, and the diffracted light diffracted by the diffraction grating 4 can be strengthened.

  As shown in FIG. 2, when the member 9 to be measured moves by x in the height direction, the first light beam L1 irradiated on the measurement surface of the member 9 to be measured is changed from the first irradiation spot P1 to the first. To the irradiation spot P1 ′. Further, the first light beam L1 reflected by the first irradiation spot P1 'of the member 9 to be measured moves from the diffraction position T1 of the diffraction grating 4 to the diffraction position T1'. Further, the first light beam L1 diffracted for the first time by the diffraction grating 4 moves from the second irradiation spot P2 of the member to be measured 9 to the second irradiation spot P2 '.

  That is, the first light beam L1 changes from the optical path AP1T1P2E to the optical path AP1'T1'P2'E. Here, since the incident angle of the first light beam L1 with respect to the measured member 9 does not change even if the measured member 9 moves by x in the height direction, the angle θ1 = the angle θ2 = the angle θ3 holds. Further, a line extending vertically from the first irradiation spot P1 in the measured member 9 in the height direction, a so-called perpendicular, and the optical path of the first light beam L1 when the measured member 9 moves by x in the height direction. Let H be the point where AP1'T1'P2'E intersects. Further, a line extending vertically from the second irradiation spot P2 in the measured member 9 in the height direction, a so-called perpendicular line, and an optical path of the first light beam L1 when the measured member 9 moves by x in the height direction. Let G be the point where AP1'T1'P2'E intersects.

  Here, the length from the first irradiation spot P1 to the first irradiation spot P1 'is equal to the length from the first irradiation spot P1' to the point H. Furthermore, since the diffraction grating 4 is disposed substantially perpendicular to the member 9 to be measured, the perpendicular extending substantially perpendicular to the height direction from the first irradiation spot P1 and the diffraction surface of the diffraction grating 4 are parallel. . Therefore, the length from the first irradiation spot P1 to the diffraction position T1 is equal to the length from the point H to the diffraction position T1 '.

  Similarly, the length from the second irradiation spot P2 to the second irradiation spot P2 ′ is equal to the length from the second irradiation spot P2 ′ to the point G, and from the diffraction position T1 to the second irradiation spot P2. And the length from the diffraction position T1 ′ to the point G are equal. As a result, the optical path length of the first light beam L1 is always constant even when the member 9 to be measured is displaced in the height direction. That is, the optical path length of the first light beam L1 does not change. When the member 9 to be measured is displaced in the height direction, only the position where the first light beam L1 enters the diffraction grating 4 changes.

  Here, since the diffraction grating 4 is disposed substantially perpendicular to the surface to be measured of the member 9 to be measured, the distance between the diffraction position T1 and the diffraction position T1 ′ is 2 of the movement amount x of the member 9 to be measured. Double 2x. That is, the amount of movement of the first light beam L1 that moves on the diffraction grating 4 is 2x, which is twice that when the member to be measured 9 is moved. Therefore, when the member 9 to be measured moves by x in the height direction, the phase of 2Kx is added to the first light beam L1. K is a wave number represented by 2π / Λ.

  In addition, since the mirror 6 is fixed, the optical path of the second light beam L2 does not change.

  Further, as shown in FIG. 1A, the light beam combining unit 14 superimposes the first light beam L1 and the second light beam L2 reflected again from the member 9 to be measured and the mirror 6 and irradiates the light receiving unit 8. Further, on the optical path between the light beam coupling portion 14 and the light receiving portion 8, a light receiving side phase plate 17 made of, for example, a quarter wavelength plate or the like is disposed.

  Here, the optical path length from the light beam splitting unit 3 to the light beam coupling unit 14 via the member to be measured 9 and the diffraction grating 4, and the optical path from the light beam splitting unit 3 to the light beam coupling unit 14 via the mirror 6 and the diffraction grating 4. The lengths are set approximately equal. That is, since the optical path lengths of the first light beam L1 and the second light beam L2 are set to be equal, even if there is a wavelength variation of the light source due to changes in atmospheric pressure, humidity, or temperature, the first light beam L1 and the second light beam L2 Can be equally affected. As a result, there is no need to perform atmospheric pressure correction, humidity correction, and temperature correction, and stable measurement can be performed regardless of the surrounding environment.

  The light receiving unit 8 includes a non-polarizing beam splitter 16 that divides light, a first polarizing beam splitter 18, and a second polarizing beam splitter 19.

  A first light receiving element 33 and a second light receiving element 34 are provided on the light exit side of the first polarizing beam splitter 18. The second polarizing beam splitter 19 is disposed so as to be inclined by 45 degrees with respect to the first polarizing beam splitter 18. A third light receiving element 35 and a fourth light receiving element 36 are provided on the light exit side of the second polarizing beam splitter 19.

  The first polarizing beam splitter 18 and the second polarizing beam splitter 19 reflect the interference light having the s-polarized component and transmit the interference light having the p-polarized component to split the light.

  A relative position information output unit 10 is connected to the light receiving unit 8. As shown in FIG. 3, the relative position information output means 10 includes a first differential amplifier 61a, a second differential amplifier 61b, a first A / D converter 62a, and a second A / D converter. 62b, a waveform correction processing unit 63, and an incremental signal generator 64.

  A first light receiving element 33 and a second light receiving element 34 are connected to the first differential amplifier 61a, and a third light receiving element 35 and a fourth light receiving element are connected to the second differential amplifier 61b. Element 36 is connected. In addition, a first A / D converter 62a is connected to the first differential amplifier 61a, and a second A / D converter 62b is connected to the second differential amplifier 61b. Yes. The first A / D converter 62 a and the second A / D converter 62 b are connected to the waveform correction processing unit 63.

1-2. Configuration of Optical Path Correction Member Next, detailed configurations of the first optical path correction member 7A and the second optical path correction member 7B will be described with reference to FIGS.
4 and 5 are explanatory views showing a state in which the member 9 to be measured is tilted, and FIG. 6 is an explanatory view showing the operation of the first optical path correcting member 7A.

  First, as shown in FIG. 4, the first irradiation spot P1 and the second irradiation spot P2 have different height positions, for example, the first irradiation spot P1 is higher than the second irradiation spot P2. A case where the member 9 to be measured is tilted in the direction of increasing in the direction will be described. Here, when the inclination angle δθ of the member 9 to be measured is about 1 degree, sin θ = θ can be set. Therefore, the formula sin θ ′ = λ / Λ−sin θ for obtaining the diffraction angle θ ′ can be approximated by θ ′ = λ / Λ−θ.

  When the member to be measured 9 is tilted at an angle δθ, the direction of the first light beam L1 reflected by the member to be measured 9 changes at an angle 2δθ. Therefore, the incident angle to the diffraction grating 4 is θ−δ2θ. At this time, the diffraction angle θ ′ diffracted by the diffraction grating 4 is θ ′ + 2δθ from the above approximate expression. When the first light beam L1 is incident on the member to be measured 9 and reflected again, the traveling direction of the first light beam L1 changes again by 2δθ. Therefore, the angle reflected again by the member to be measured 9 remains θ ′ before and after it is tilted and does not change.

  For this reason, even if the member 9 to be measured is tilted in different directions in the height direction in the first irradiation spot P1 and the second irradiation spot P2, only the position of the first light beam L1 is shifted substantially in parallel. The direction does not change. Therefore, the first light beam L1 and the second light beam L2 incident on the light receiving unit 8 can be kept substantially parallel, and the first light beam L1 and the second light beam L2 can be superimposed and interfere with each other.

Next, the case where the member to be measured 9 is tilted around a line O that is substantially parallel to the line connecting the first irradiation spot P1 and the second irradiation spot P2 will be described with reference to FIGS.
As shown in FIG. 5, when the member 9 to be measured is tilted about the line O, the traveling direction of the first light beam L1 changes. Here, the traveling direction of the first light beam L1 when the member to be measured 9 is not inclined is defined as an optical axis direction Z. A direction orthogonal to the optical axis direction Z and orthogonal to the grating vector direction K of the diffraction grating 4 is defined as a first direction X, and the direction orthogonal to the optical axis direction Z and the first direction X is defined as a second direction. The direction is Y. The first direction X indicates the displacement direction of the present invention.

  For example, when the member to be measured 9 is inclined in the direction of the arrow + around the line O, the traveling direction of the first light beam L1 is the first in the plane M1 formed by the optical axis direction Z and the first direction X. It is inclined toward the + side of the direction X of 1, that is, toward the light ray (a). When the member to be measured 9 is tilted in the direction of the arrow − around the line O, the traveling direction of the first light beam L1 is the − side of the first direction X in the plane M1, that is, the direction of the light beam (b). Lean to.

  When the traveling direction of the first light beam L1 is tilted in the direction shown in FIG. 5, the first light beam L1 and the second light beam L2 cannot be kept parallel in the light beam coupling unit 14, and the first light beam L1 is lost. And the second light beam L2 may not interfere accurately. As a result, it is conceivable that the interference signal between the first light beam L1 and the second light beam L2 is greatly reduced.

  Therefore, in the displacement detection device 1 of this example, the first optical path correction member 7A that corrects the optical path of the first light beam L1 is provided between the member to be measured 9 and the light beam coupling portion 14.

FIG. 6 is an explanatory view of the first optical path correction member 7A viewed from the plane M1.
As shown in FIG. 6, the first optical path correction member 7A has a curvature in the plane M1. That is, the first optical path correction member 7A is a cylindrical lens that can collect the first light beam L1 only in the first direction X.

  Further, as shown in FIG. 5, when the first light beam L1 whose traveling direction is inclined is extended in the optical axis direction Z on the plane M1, almost all the light beams intersect in the vicinity of the virtual point Q. As shown in FIG. 6, the focal position of the first optical path correction member 7A substantially coincides with the virtual point Q. That is, the focal point Fb of the first optical path correction member 7A is set to be substantially equal to the distance from the first optical path correction member 7A to the provisional name point Q.

  Therefore, the optical path of the first light beam L1 incident on the first optical path correction member 7A is corrected by the first optical path correction member 7A. When the first light beam L1 passes through the first optical path correction member 7A, the first light beam L1 can be kept substantially parallel to the optical axis direction Z. Thereby, the traveling directions of the first light beam L1 and the second light beam L2 can be kept substantially parallel, and the first light beam L1 and the second light beam L2 can be reliably interfered with each other.

  In addition, as shown in FIG. 1A, the first convergent lens 5 </ b> A is also disposed between the light beam splitting unit 3 and the member 9 to be measured. By this first converging lens 5A, the first light beam L1 incident on the first optical path correction member 7A is made into convergent light. Thereby, the 1st light beam L1 after passing 7 A of 1st optical path correction members can be made into parallel light reliably. The focal position of the first converging lens 5A is preferably set to a virtual point Q that is substantially equal to the focal position of the first optical path correction member 7A.

  Further, as shown in FIG. 1, the second optical path correction member 7B and the second converging lens 5B are also arranged on the side of the mirror 6 that is fixed and whose surface is difficult to tilt. Thereby, the aberration which arises in the optical path of the 1st light beam L1 and the 2nd light beam L2 can be made equal. As a result, it is possible to eliminate a difference in wavefront when the first light beam L1 and the second light beam L2 interfere with each other, and to obtain a large interference signal.

  Thereby, according to the displacement detection apparatus 1 of the present example, by providing the optical path correction member that corrects the optical path, even when the measurement surface of the member to be measured 9 is inclined, the interference signal hardly changes and stable measurement is performed. It can be performed.

  In this example, the example in which the cylindrical lens is used as the first optical path correction member 7A has been described. However, the present invention is not limited to this. As the first optical path correction member 7A, any optical element capable of condensing the first light beam L1 only in the first direction X may be used.

FIG. 7 is a plan view showing the diaphragm member, and FIG. 8 is an explanatory diagram showing a state of the first light beam L1 when the diaphragm member is provided.
Here, as shown in FIG. 8, when the first light beam L1 passes through the first optical path correction member 7A with the member 9 to be measured tilted in the direction shown in FIG. 5, the first light beam L1 is Shifting in one direction in the first direction X in the first direction X is parallel to the optical axis direction Z. Therefore, the portion where the first light beam L1 and the second light beam L2 overlap is only the shaded portion J1 shown in FIG. 8, and the portion outside the shaded portion J1 does not overlap and does not interfere. As a result, the interference signal obtained by the light receiving unit 8 changes, and there is a possibility that stable measurement cannot be performed.

  Therefore, as shown in FIGS. 7 and 8, an aperture member 20 having an opening 20 </ b> A may be disposed between the first optical path correction member 7 </ b> A and the light beam coupling portion 14. As shown in FIG. 7, the opening 20A of the aperture member 20 is a long hole, and is wider in the second direction Y than the first direction X where the shift amount of the first light beam L1 is large. By providing this diaphragm member 20, it is possible to remove light rays outside the hatched portion J1 shown in FIG. 8 in advance. As a result, as shown in FIG. 8, even when the first light beam L1 is shifted in the first direction X, the amount of change in the interference signal obtained by the light receiving unit 8 can be reduced, and stable measurement is performed. be able to.

  Instead of providing the diaphragm member 20, the opening in the first direction X of the first light receiving element 33, the second light receiving element 34, the third light receiving element 35, and the fourth light receiving element 36 in the light receiving unit 8 is provided. It may be narrowed. That is, it may be set so that only a portion where the first light beam L1 and the second light beam L2 overlap is received.

1-3. Operation of Displacement Detection Device Next, the operation of the displacement detection device 1 of this example will be described with reference to FIGS.

  As shown in FIG. 1, the s-polarized light emitted from the light source is collimated by the lens 11 to become parallel light. Then, the collimated light collimated by the lens 11 enters the light beam splitting unit 3. The light incident on the light beam splitting unit 3 is split into a first light beam L1 and a second light beam L2. The first light beam L1 enters the diffraction position T1 of the diffraction grating 4 reflected by the member 9 to be measured at an incident angle π / 2−θ.

  The first light beam L1 incident on the diffraction grating 4 is diffracted by the diffraction grating 4, and the diffracted first light beam L1 is incident on the member to be measured 9 again. Next, the first light beam L1 incident on the member to be measured 9 again is reflected by the member to be measured 9 and is applied to the light beam coupling unit 14 via the phase plate 12 and the first optical path correction member 7A.

  The first light beam L1 passes through the first optical path correction member 7A, so that the optical path is corrected as shown in FIGS. Further, the first light beam L1 passes through the phase plate 12 that is a half-wave plate. Here, the optical axis of the phase plate 12 is inclined 45 degrees with respect to the polarization direction of incident light. Therefore, the first light beam L1 passes through the phase plate 12 and is converted from s-polarized light to p-polarized light. And the 1st light beam L1 which passed the phase plate 12 injects into the light beam coupling part 14 which is a polarization beam splitter.

  On the other hand, the second light beam L <b> 2 irradiated on the mirror 6 is reflected by the mirror 6 and irradiated on the diffraction grating 4. Then, similarly to the first light beam L1, the second light beam L2 is diffracted by the diffraction grating 4 and enters the mirror 6 again. Next, the second light beam L2 is reflected again by the mirror 6, and is irradiated onto the light beam coupling portion 14 via the dummy glass 13 and the second optical path correction member 7B.

  The mirror 6 has an optical path length from the light beam splitting unit 3 to the light beam coupling unit 14 via the diffraction grating 4 in the first light beam L1 and a light beam coupling from the light beam splitting unit 3 to the light beam coupling unit 4 in the second light beam L2. The optical path lengths to the unit 14 are arranged to be equal. Therefore, even if there is a wavelength variation of the light source due to changes in atmospheric pressure, humidity, and temperature, it is possible to equalize the effects of the first light beam L1 and the second light beam L2.

  Further, both the first light beam L1 and the second light beam L2 are incident on the diffraction grating 4 to be diffracted. Thereby, even if the diffraction angle of the diffraction grating 4 changes due to a temperature change, the influences of the first light beam L1 and the second light beam L2 can be made equal.

  Further, a light receiving side phase plate 17 that is a quarter wavelength plate is disposed between the light beam coupling portion 14 and the light receiving portion 8. The optical axis of the light receiving side phase plate 17 is inclined 45 degrees with respect to the polarization direction of incident light. The first light beam L1 and the second light beam L2 superimposed by the light beam coupling unit 14 pass through the light receiving side phase plate 17 and become circularly polarized light beams that are opposite to each other. Since the mutually opposite circularly polarized lights are on the same optical path, they can be regarded as linearly polarized light beams La that rotate according to the phase difference between the two light beams L1 and L2 by being superimposed.

  The light beam La is applied to the non-polarizing beam splitter 16. The non-polarizing beam splitter 16 splits the light beam La into two lights. The light beam La reflected by the non-polarization beam splitter 16 enters the first polarization beam splitter 18, and the light beam La transmitted through the non-polarization beam splitter 16 enters the second polarization beam splitter 19.

  As described above, the light beam La incident on the first polarization beam splitter 18 is obtained by superimposing the two reverse circularly polarized first light beam L1 and second light beam L2. Therefore, the first light beam L1 and the second light beam L2 have a p-polarized component and an s-polarized component, respectively, with respect to the first polarizing beam splitter 18. Accordingly, the first light beam L1 and the second light beam L2 that have passed through the first polarizing beam splitter 18 interfere with each other in polarized light having the same polarization direction. Therefore, the first light beam L1 and the second light beam L2 can be caused to interfere with each other by the first polarizing beam splitter 18.

  Similarly, in the first light beam L1 and the second light beam L2 reflected by the first polarization beam splitter 18, polarized light having the same polarization direction interferes with the first polarization beam splitter 18. Therefore, interference can be caused by the first polarization beam splitter 18.

  The interference light with the first light beam L1 and the second light beam L2 transmitted through the first polarization beam splitter 18 is received by the first light receiving element 33. The interference light with the first light beam L1 and the second light beam L2 reflected by the first polarization beam splitter 18 is received by the second light receiving element 34.

  Further, the polarization direction of the linearly polarized light incident on the first polarizing beam splitter 18 is rotated 180 degrees when the member 9 to be measured moves by Λ / 2 in the height direction. Here, the first light receiving element 33 and the second light receiving element 34 extract components having polarization directions different from each other by 90 degrees. Therefore, signals that are photoelectrically converted by the first light receiving element 33 and the second light receiving element 34 are signals that are 180 degrees out of phase.

  Further, the light beam La incident on the second polarizing beam splitter 19 is split by the second polarizing beam splitter 19 into two components whose polarization directions are orthogonal to each other. The s-polarized component of this linearly polarized light is reflected by the second polarization beam splitter 19 and received by the third light receiving element 35. The p-polarized component passes through the second polarizing beam splitter 19 and is received by the fourth light receiving element 36.

  Further, the signals photoelectrically converted by the third light receiving element 35 and the fourth light receiving element 36 have a phase difference of 180 degrees.

  Here, as shown in FIG. 2, when the member 9 to be measured moves by x in the height direction, the first light beam L1 irradiated on the measurement surface of the member 9 to be measured is irradiated from the irradiation spot P1 to the irradiation spot P1 ′. Move to. Further, the first light beam L1 reflected by the member to be measured 9 moves from the diffraction position T1 of the diffraction grating 4 to the diffraction position T1 '. Here, since the diffraction grating 4 is disposed substantially perpendicular to the surface to be measured of the member 9 to be measured, the distance between the diffraction position T1 and the diffraction position T1 ′ is the distance between the irradiation spot P1 and the irradiation spot P1 ′. 2 ×, which is twice as large as That is, the amount of movement of the first light beam L1 that moves on the diffraction grating 4 is 2x, which is twice that when the member to be measured 9 is moved. Therefore, a phase of 2Kx is added to the first light beam L1.

At this time, the measured member 9 has a signal I ₁ obtained by the first light receiving element 33, a signal I ₂ obtained by the second light receiving element 34, a signal I ₃ obtained by the third light receiving element 35, and a fourth signal. A signal I ₄ obtained by the light receiving element 36 is expressed by, for example, the following formula 3.
[Formula 3]




Here, δ indicates the initial phase, I0 indicates the light amount of the first light beam L1 returning from the member 9 to be measured, and Ir indicates the light amount of the second light beam L2 returning from the mirror 6. ing.

  In the present embodiment, the second polarizing beam splitter 19 that divides the light beams received by the third light receiving element 35 and the fourth light receiving element 36 is inclined by 45 degrees with respect to the first polarizing beam splitter 18. Arranged. Therefore, the signal obtained in the third light receiving element 35 and the fourth light receiving element 36 is 90% of the signal obtained in the first light receiving element 33 and the second light receiving element 34 as shown in Equation 3. Is out of phase.

  Therefore, the Lissajous signal can be obtained by using signals obtained from the first light receiving element 33, the second light receiving element 34, the third light receiving element 35, and the fourth light receiving element 36 as the sin signal and the cos signal. it can. The phase angle θ as shown in FIG. 3B can be obtained from this Lissajous signal.

  Signals obtained by these light receiving elements are calculated by the relative position information output means 10, and the displacement amount of the measured surface is counted.

  As shown in FIG. 3, for example, in the relative position information output unit 10 of this example, first, signals obtained by the first light receiving element 33 and the second light receiving element 34 are different in phase by 180 degrees from each other. Differential amplification is performed by the differential amplifier 61a to cancel the DC component of the interference signal.

  This signal is A / D converted by the first A / D converter 62a, and the signal amplitude, offset, and phase are corrected by the waveform correction processing unit 63. This signal is calculated in the incremental signal generator 64 as an A-phase incremental signal, for example.

  Similarly, the signals obtained by the third light receiving element 35 and the fourth light receiving element 36 are differentially amplified by the second differential amplifier 61b and A / D by the second A / D converter 62b. Converted. Then, the signal amplitude, offset, and phase are corrected by the waveform correction processing unit 63 and output from the incremental signal generator 64 as a B phase incremental signal that is 90 degrees different from the A phase.

  The two-phase incremental signal obtained in this way is discriminated forward or reverse by a pulse discriminating circuit or the like (not shown), whereby the amount of displacement of the member 9 to be measured is positive or negative. It can be detected.

  Further, by counting the number of pulses of the incremental signal with a counter (not shown), it is possible to measure how many periods of the interference light intensity of the first light beam L1 and the second light beam L2 have changed. Thereby, the displacement amount of the member 9 to be measured is detected.

  Note that the relative position information output by the relative position information output unit 10 of this example may be the above-described two-phase incremental signal, or a signal including the displacement amount and the displacement direction calculated therefrom. .

  For example, when the grating pitch Λ of the diffraction grating 4 is set to 0.5515 μm, the wavelength λ is set to 780 nm, and the incident angle and diffraction angle of the diffraction grating 4 are set to 45 °, the member to be measured 9 moves 0.5515 μm in the height direction. An example will be described.

  When the member to be measured 9 moves 0.5515 μm in the height direction, the first light beam L1 moves twice on the diffraction grating 4 by 0.5515 μm, that is, by two pitches. Therefore, the first light beam L <b> 1 can obtain the brightness of the light twice by the light receiving unit 8. That is, one period of the obtained signal is 0.5515 μm / 2 = 0.275575 μm.

2. Second Embodiment of Displacement Detection Device Next, a displacement detection device according to a second embodiment will be described with reference to FIGS.
FIG. 9 is a schematic configuration diagram illustrating a configuration of the displacement detection device. FIG. 10 is an explanatory diagram showing a configuration around the light source.

  The displacement detection apparatus 101 according to the second embodiment uses an optical heterodyne method. The difference between the displacement detection device 101 according to the second embodiment and the displacement detection device 1 according to the first embodiment is the configuration of the light source and the light receiving unit. Therefore, here, the configuration around the light source and the light receiving unit will be described, and the same reference numerals are given to the portions common to the displacement detection device 1 according to the first embodiment, and the duplicated description will be omitted.

  As shown in FIGS. 9 and 10, the displacement detection apparatus 101 includes a light source 102, a light beam splitter 113 that is a polarization beam splitter, a diffraction grating 4, a mirror 6, two converging lenses 5 </ b> A and 5 </ b> B, 2 There are two optical path correction members 7A and 7B, a light beam coupling portion 14, and a light receiving portion 111. In addition, the displacement detection device 101 includes a signal processing circuit 112 that is a relative position information output unit that outputs relative position information (displacement information) in the height direction of the member 9 to be measured.

  As shown in FIG. 10, the light source 102 is composed of an axial Zeeman laser, and emits circularly polarized light beams having mutually opposite frequencies and different frequencies. Light emitted from the light source 102 enters the quarter-wave plate 103. And the light radiate | emitted from the light source 102 by passing through this quarter wavelength plate 103 turns into a linearly polarized light mutually orthogonally crossed. A first polarizing beam splitter 104 is disposed on the exit side of the quarter-wave plate 103. The light that has become linearly polarized light is split by the first polarization beam splitter 104.

For example, the first light beam L <b> 1 composed of p-polarized light having a frequency f ₀ out of linearly polarized light is transmitted through the polarization beam splitter 104. The first light beam L1 is collected by the first condenser lens 105A and is incident on the first polarization maintaining fiber 106A. The second light flux L2 consisting of s-polarized light having a frequency f _r of the light becomes linearly polarized light is reflected by the polarization beam splitter 104. Then, the second light beam L2 is collected by the second condenser lens 105B and is incident on the second polarization maintaining fiber 106B.

  At the output end of the first polarization maintaining fiber 106A, the polarization axis is aligned so that the output light becomes p-polarized light. Further, at the emission end of the second polarization maintaining fiber 106B, the polarization axis is aligned so that the emitted light becomes s-polarized light.

  As shown in FIG. 9, a second polarization beam splitter 108 is disposed on the emission end side of the first polarization maintaining fiber 106A and the second polarization maintaining fiber 106B. Further, a first collimating lens 107A is disposed between the first polarization maintaining fiber 106A and the second polarization beam splitter 108, and the second polarization maintaining fiber 106B and the second polarization beam splitter are disposed. A second collimating lens 107 </ b> B is disposed between 108.

  When the first light beam L1 propagated through the first polarization maintaining fiber 106A is emitted from the first polarization maintaining fiber 106A, it is collimated into parallel light by the first collimating lens 107A. Then, the first light beam L1 collimated to the parallel light is incident on the second polarization beam splitter 108.

  Further, when the second light beam L2 propagated through the second polarization maintaining fiber 106B is emitted from the second polarization maintaining fiber 106B, it is collimated into parallel light by the second collimating lens 107B. Then, the second light beam L2 collimated to the parallel light is incident on the second polarization beam splitter 108.

  The first light beam L1 passes through the second polarization beam splitter 108 and enters the light beam splitter 113 that is a polarization beam splitter. The second light beam L2 is incident on the light beam splitting unit 113 reflected by the second polarization beam splitter 108.

  The first light beam L1 that has passed through the light beam splitting unit 113 is condensed by the first converging lens 5A and becomes convergent light. Then, the first light beam L1 that has passed through the first converging lens 5A is reflected by the member to be measured 9 and enters the diffraction grating 4. Then, the first light beam L1 is diffracted by the diffraction grating 4. The diffracted first light beam L1 is reflected again by the member to be measured 9, and enters the first optical path correction member 7A. The first light beam L1 incident on the first optical path correction member 7A has its optical path corrected by the first optical path correction member 7A and is returned from the convergent light to parallel light (collimated beam). The light enters a certain light beam coupling portion 14.

  The second light beam L2 reflected from the light beam splitting unit 113 is collected by the second convergent lens 5B, reflected by the mirror 6, and incident on the diffraction grating 4. Then, the second light beam L2 is diffracted by the diffraction grating 4 and reflected by the mirror 6 again. The reflected second light beam L2 is returned from the converged light to parallel light (collimated beam) by the second optical path correction member 7B, and is incident on the light beam combining unit 14 which is a polarization beam splitter.

  The configurations and functions of the two converging lenses 5A and 5B, the diffraction grating 4, the mirror 6, the first optical path correction member 7A, and the second optical path correction member 7B are the same as those of the displacement detection apparatus according to the first embodiment. The description thereof is omitted here since it is the same as 1.

  The light beam combining unit 14 superimposes the first light beam L 1 and the second light beam L 2 diffracted by the diffraction grating 4 and irradiates the light receiving unit 111. The light receiving unit 111 receives the light beam La that has passed through the polarizing plate 110 and interfered therewith. A signal processing circuit 112 is connected to the light receiving unit 111.

The interference signal obtained by the light receiving unit 111 is expressed by the following formula 4, for example.
[Formula 4]

Here, I0 is the light quantity of the first light beam L1 returning from the measurement member 9, I _r shows the light intensity of the second light beam L2 returned from the mirror 6, t is represents time Yes.

The interference signal obtained by the light receiving unit 111 is transmitted to the signal processing circuit 112, and the signal processing circuit 112 calculates relative position information (displacement information) in the height direction of the measurement target surface of the member 9 to be measured. Here, the frequency difference f ₀ -f _r of the light source 102 is an axial Zeeman laser, for about several MHz, the interference signal shown by the formula 4 can be easily detected by a pin photodiode or the like. Since the signal has a constant frequency, the signal processing circuit 112 can detect the phase difference 2Kx without using the amplitude information of the signal.

  As a result, according to the displacement detection device 101 according to the second embodiment, as compared with the method for obtaining the phase angle from the sin signal and the cos signal as in the displacement detection device 1 according to the first embodiment. The phase difference 2Kx can be detected even with a very weak signal. Thereby, when the reflectance of the measurement surface of the member 9 to be measured is low, the displacement of the member 9 to be measured can be reliably detected even when the measurement surface of the member 9 to be measured is rough.

  Furthermore, if an APD (avalanche photodiode) having an amplification effect on the signal is used as the light receiving unit 111, it is possible to measure even a member to be measured having a surface with a lower reflectance.

  Since other configurations are the same as those of the displacement detection device 1 according to the first embodiment, description thereof will be omitted. Also with the displacement detection device 101 having such a configuration, it is possible to obtain the same operational effects as those of the displacement detection device 1 according to the first embodiment described above.

3. Third Embodiment of Displacement Detection Device Next, a displacement detection device according to a third embodiment will be described with reference to FIG.
FIG. 11 is an explanatory diagram illustrating a configuration around the light source according to the third displacement detection apparatus.

  The displacement detection device 201 according to the third embodiment uses an optical heterodyne method, similarly to the displacement detection device 101 according to the second embodiment. The difference between the displacement detector 201 according to the third embodiment and the displacement detector 101 according to the second embodiment is the configuration around the light source. Therefore, here, the configuration around the light source will be described, and portions common to the displacement detection apparatus 101 according to the second embodiment are denoted by the same reference numerals, and redundant description is omitted.

As shown in FIG. 11, in the displacement detection device 201 according to the third embodiment, a coherent light source is used as the light source 202. Further, light having a frequency f ₀ is emitted from the light source 202.

An acousto-optic modulator (AOM) 204 is disposed between the light source 202 and the first polarization maintaining fiber 106A and the second polarization maintaining fiber 106B. A driver 203 is connected to the acousto-optic modulator 204. The acousto-optic modulator 204 is driven by an electric signal having a frequency f ₁ by a driver 203. Then, the acousto-optic modulator 204 adds the frequency f ₁ applied from the driver 203 to the light emitted from the light source 202.

In addition, from the exit side of the acousto-optic modulator 204, an optical frequency _{f 0,} the light of the frequency _f 0 + _{f 1} shifted from the frequency _{f 0} by a frequency _{f 1} is emitted. Light of frequency _{f 0,} through a first focusing lens 205A is incident on the first polarization maintaining fiber 106A, the light of the frequency _f 0 + _{f 1} is first through the second focusing lens 205B 2 Is incident on the polarization maintaining fiber 106B.

Further, an interference signal obtained by the light receiving unit 111 in the displacement detection apparatus 201 according to the third embodiment is expressed by, for example, the following formula 5.
[Formula 5]

Note that t represents time.

Frequency _{f 1} to be shifted by the acousto-optic modulator 204, the value of the large tens MHz than several MHz frequency difference _f 0 -f _r of the light source 102 in the displacement detection apparatus 101 according to an exemplary second embodiment can do. The displacement speed of the detectable surface to be measured is proportional to the frequency _{f 1} and the frequency _f 0 -f _r. Therefore, the displacement detection apparatus 201 according to the third embodiment can detect a faster displacement of the member 9 to be measured. Further, depending on the value of the frequency f ₁ shifted by the acousto-optic modulator 204, an APD (avalanche photodiode) having a response frequency higher than that of the pin photodiode and having an amplifying function can be used as the light receiving unit 111.

  Since other configurations are the same as those of the displacement detection device 1 according to the first embodiment and the displacement detection device 101 according to the second embodiment, their descriptions are omitted. Even with the displacement detection device 201 having such a configuration, the same operational effects as the displacement detection device 1 according to the first embodiment and the displacement detection device 101 according to the second embodiment described above can be obtained. Can do.

4). Fourth Embodiment of Displacement Detection Device Next, a displacement detection device according to a fourth embodiment will be described with reference to FIG.
FIG. 12 is an explanatory diagram illustrating a configuration around the light source according to the fourth displacement detection apparatus.

  The displacement detection device 301 according to the fourth embodiment uses a pseudo optical heterodyne method using an optical waveguide. The difference between the displacement detector 301 according to the fourth embodiment and the displacement detector 101 according to the second embodiment is the configuration around the light source. Therefore, here, the configuration around the light source will be described, and portions common to the displacement detection apparatus 101 according to the second embodiment are denoted by the same reference numerals, and redundant description is omitted.

  As shown in FIG. 12, a displacement detection device 301 according to the fourth embodiment includes a light source 302, a drive circuit 303, and an optical waveguide member 304. The light source 302 is a coherent light source such as a laser diode.

The optical waveguide member 304 includes an optical waveguide 304b that branches in a Y shape and an optical modulator 304a that includes a pair of electrodes. The optical modulator 304a is arranged in one of the two branched optical waveguides 304b. A predetermined voltage V _m sin (ω _m t + φ ₀ ) is applied to the optical modulator 304 a from the drive circuit 303. Here, V _m is a modulation voltage, and ω _m indicates an angular frequency. Φ ₀ is a phase adjusted by a phase adjustment circuit (not shown).

As the optical waveguide 304b, for example, LiNbO ₃ that is a dielectric material is used. In addition, light from the light source 302 enters the optical waveguide 304b using, for example, a lens. When the light source 302 is a laser diode, the optical waveguide member 304 may be directly bonded to the light source 302 so that the emission end of the light source 302 and the incident portion of the optical waveguide 304b are in direct contact with each other.

The light incident on the optical waveguide 304b is divided into a first light beam L1 that is object light and a second light beam L2 that is reference light. The first light beam L1 passes through the optical waveguide 304b provided with the optical modulator 304a, out of the two branched optical waveguides 304b. The phase of the first light beam L1 is modulated by applying a voltage V _m sin (ω _m t + φ ₀ ) by the optical modulator 304a. The modulated first light beam L1 is incident on the first polarization maintaining fiber 106A. The second light beam L2 that is the reference light passes through the optical waveguide 304b that is not provided with the optical modulator 304a, out of the two branched optical waveguides 304b. The second light beam L2 enters the second polarization maintaining fiber 106B without being modulated.

Here, the amplitude E _{0 of} the first light beam L1 that is the object light and the amplitude _Er of the second light beam L2 that is the reference light are expressed by the following Expression 6, for example.
[Formula 6]
E ₀ = E ₁ cos (ω ₀ t + m _p sin (ω _m t + φ ₀ ) + φ ₁ )
E _r = E ₂ cos (ω ₀ t + φ ₂ )
Here, m _p represents the phase modulation index, and ω ₀ represents the angular frequency of the light emitted from the light source 302. Φ ₁ and φ ₂ indicate initial phases. Further, t represents time, and E ₁ and E ₂ represent electric field amplitudes.

Further, an interference signal obtained by the light receiving unit 111 in the displacement detection apparatus 301 according to the fourth embodiment is expressed by, for example, the following Expression 7.
[Formula 7]


Here, V _DET indicates a voltage amplitude obtained by the light receiving unit 111, and J ₁ (m _p ) is a Bessel function.

In the displacement detection device 301 according to the fourth embodiment, the phase difference 2Kx can be detected similarly to the displacement detection devices 101 and 201 according to the second and third embodiments described above. Further, since the angular frequency ω _{m of the} voltage applied by the optical modulator 304a can be set to several tens of MHz or more, it can be applied to high-speed displacement.

  Further, since the optical waveguide 304b provided in the optical waveguide member 304 can be formed very small, the apparatus is significantly smaller than the displacement detection apparatuses 101 and 201 according to the second and third embodiments. It is possible to

    Other configurations are the same as those of the displacement detection device 1 according to the first embodiment and the displacement detection devices 101 and 201 according to the second and third embodiments, and thus description thereof is omitted. Also with the displacement detection device 301 having such a configuration, the displacement detection device 1 according to the first embodiment described above, the displacement detection device 101 according to the second embodiment, and the third embodiment. It is possible to obtain the same effect as that of the displacement detector 201 according to the above.

  The present invention is not limited to the embodiment described above and shown in the drawings, and various modifications can be made without departing from the scope of the invention described in the claims. In the embodiment described above, the light emitted from the light source may be supplied not only in the gas but also in a liquid or vacuum space.

  DESCRIPTION OF SYMBOLS 1,101,201,301 ... Displacement detection apparatus 2,102,202,302 ... Light source 3,113 ... Light beam splitting part (light beam coupling part), 4 ... Diffraction grating, 5A ... First convergent lens, 5B ... 2nd convergent lens, 6 ... mirror (reflecting part), 7A ... 1st optical path correction member, 7B ... 2nd optical path correction member, 8, 111 ... light receiving part, 9 ... measured member, 10 ... relative position information 11: lens, 12: phase plate, 13: dummy glass, 14: light beam coupling unit, 16: non-polarization beam splitter, 17: light receiving side phase plate, 18: first polarization beam splitter, 19: second 20 ... aperture member, 33 ... first light receiving element, 34 ... second light receiving element, 35 ... third light receiving element, 36 ... fourth light receiving element, 37 ... absolute For value Light receiving section, 37C ... fifth light receiving element, 37D ... sixth light receiving element, 38 ... differential comparator, 112 ... signal processing circuit (relative position information output means), 204 ... acousto-optic modulator, 304 ... optical waveguide Member, 304a: optical modulator, 304b: optical waveguide, L1: first light beam, L2: second light beam, P1, P1 ′: first irradiation spot, P2, P2 ′: second irradiation spot, T1 , T1 '... diffraction position, Λ ... grating pitch, K ... grating vector direction, X ... first direction (displacement direction), Y ... second direction, Z ... optical axis direction M1, plane, Q ... virtual point Fb ... Focus

Claims (7)

A light source that emits light;
A first light beam that causes the light emitted from the light source to enter the member to be measured, and a light beam dividing unit that divides the light beam into a second light beam that serves as reference light,
The first light beam divided by the light beam splitting unit and reflected by the surface to be measured of the member to be measured is diffracted, and the diffracted first light beam is incident again on the surface to be measured of the member to be measured. A transmissive diffraction grating;
A reflecting portion that reflects the second light flux divided by the light flux splitting portion;
A light beam coupling unit that superimposes the first light beam diffracted by the diffraction grating and reflected again by the surface to be measured, and the second light beam reflected by the reflection unit;
A light receiving unit that receives interference light of the first light beam and the second light beam superimposed by the light beam coupling unit;
The first light beam provided between the light beam coupling portion and the member to be measured and tilted in the traveling direction by tilting the member to be measured and the second light beam are substantially parallel in the light beam coupling portion. An optical path correction member for correcting the optical path of the first light flux so as to maintain
Relative position information output means for outputting displacement information in the height direction of the surface to be measured based on an interference signal of interference light received by the light receiving unit;
Displacement detection device comprising: The optical path correction member is arranged in a plane formed by an optical axis direction that is a traveling direction of the first light flux and a displacement direction that is orthogonal to the optical axis direction and a grating vector direction of the diffraction grating. The displacement detection device according to claim 1, wherein the traveling direction of the luminous flux is adjusted. The displacement detection device according to claim 2, wherein the optical path correction member has a curvature in the plane and condenses the first light flux only in the displacement direction. The first light beam whose traveling direction is tilted by tilting the member to be measured and the first light beam in a normal traveling direction when the member to be measured is not tilted are the light in the plane. 4. The focal position of the optical path correction member is positioned in the vicinity of a temporary point where the first light beam whose traveling direction is inclined and the first light beam in the normal traveling direction intersect when extending in the axial direction. The displacement detection device described in 1. The displacement detection device according to any one of claims 2 to 4, wherein a diaphragm member that restricts a light amount in the displacement direction of the first light flux is provided between the light receiving unit and the member to be measured. The converging lens for converting the first light flux from parallel light into convergent light that converges only in the displacement direction is provided between the light source and the optical path correcting member. Displacement detector. The displacement detection device according to claim 1, wherein the optical path correction member is a cylindrical lens.