JP5260261B2 - Polarization separation interferometer and polarization separation interferometer type length measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cost, and simplify adjustment by reducing the optical components of a polarization-split interferometer. <P>SOLUTION: In the polarization-split interferometer which branches light emitted from a light source 102 into measuring light and reference light, performs polarization splitting of light acquired by reflecting the measuring light with a reflection mirror and the reference light by a first polarization beam splitter 105 and makes them interfere; a second polarization beam splitter 106 for performing polarization splitting of transmitted light of the measuring light and reflected light of the reference light, is arranged with its reflection surface directed to a direction to be indicated when rotated by 45 degrees around an incident light axis from a reference position; a third polarization beam splitter 107 for performing polarization splitting of the reflected light of the measuring light and transmitted light of the reference light, is arranged with its reflection surface directed to a direction to be indicated when rotated by 45 degrees around its incident light axis from a reference position; and the outputs of the second and third polarization beam splitters, each of which is interference light between the measuring light and the reference light, are optically detected. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a polarization separation interferometer applied to high-resolution displacement measurement and the like.

As an interferometer applied to a measuring instrument that requires high resolution in displacement measurement, the measurement light reflected by a reflector installed on the measurement object is split into measurement light and reference light. The light transmitted through the λ / 4 plate (1/4 wavelength plate) and the reference light are polarized and separated into transmitted light and reflected light by the first polarization beam splitter, respectively, and the second, A configuration in which interference light between measurement light and reference light is detected by a third polarization beam splitter is known.
Here, each component of the measurement light and the reference light transmitted or reflected by the first polarization beam splitter is composed of polarization components orthogonal to each other. For this reason, in order to extract the interference signal from the transmitted light or reflected light of the first polarizing beam splitter by the second and third polarizing beam splitters, on the incident side of the second and third polarizing beam splitters, respectively. A λ / 2 plate (1/2 wavelength plate) rotated by 22.5 degrees with respect to the optical axis of the optical axis is inserted, and the polarization state of each component of the measurement light and the reference light is rotated by 45 degrees. It was necessary to equally divide each component of the measurement light and the reference light by the polarization beam splitter 3 and to make the polarization states coincide (for example, see Patent Document 1).

JP-A-7-253303

However, the conventional polarization separation type interferometer is expensive because it is composed of a large number of expensive optical components, and the optical components are accurately arranged with respect to the optical axis, and the rotation angle of the λ / 2 plate is Adjustment was necessary and the structure was large.
Therefore, in order to obtain a configuration that is cheaper, easy to adjust, and downsized, it has been required to reduce the number of components as much as possible.

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a polarization separation type interferometer that can be easily adjusted and reduced in size, by reducing the number of optical components, and An object of the present invention is to provide a length measuring device using a polarization separation type interference method.

In order to achieve the above-mentioned object, the present invention splits outgoing light from a light source into measurement light and reference light, and first sets polarization components orthogonal to each other of light obtained by reflecting the measurement light on a reflection mirror and the reference light. A polarization separation type interferometer that separates and interferes with the transmitted light and the reflected light by the polarization beam splitter, and detects the interfered light, respectively, wherein the polarization separation type interferometer is the first beam splitter. The second polarization beam splitter that polarizes and separates the transmitted light of the measurement light and the reflected light of the reference light, and the polarized light of the reflected light of the measurement light and the transmitted light of the reference light in the first beam splitter. A third polarization beam splitter, wherein the second polarization beam splitter has a reflection direction of incident light in a reference direction that reflects only the reflected light of the reference light at the first polarization beam splitter. The third polarization beam splitter is arranged so as to be rotated 45 degrees to the left or right about the optical axis of the incident light, and the reflection direction of the incident light is the first polarization beam splitter of the measurement light. With respect to a reference direction that reflects only the reflected light of the incident light, it is arranged by being rotated 45 degrees to the left or right about the optical axis of the incident light, and the light emitted from the light source is split into measurement light and reference light. A polarization beam splitter, and the measurement light reflected by the reflection mirror and transmitted by the λ / 4 plate and the reference light are incident on the first polarization beam splitter, and the measurement light and the Polarized components of the reference light that are orthogonal to each other are polarized and separated into transmitted light and reflected light by the first polarizing beam splitter, respectively, and the second polarized beam that is interference light between the measurement light and the reference light Splitter and third polarization It has a photodetector for detecting at least one of transmitted light and reflected light of the beam splitter .

Further, according to the present invention, the light emitted from the light source is branched into measurement light and reference light, and polarized light components of the light obtained by reflecting the measurement light by a reflection mirror and the reference light are orthogonal to each other. A polarization separation type interferometer that detects the light that has interfered with each other by separating the transmitted light and the reflected light, and the polarization separation type interferometer detects the measurement light in the first beam splitter. A second polarization beam splitter that polarization-separates the transmitted light of the reference light and the reflected light of the reference light, and a third polarization that polarization-separates the reflected light of the measurement light and the transmitted light of the reference light in the first beam splitter The second polarization beam splitter has a reflection direction of incident light with respect to a reference direction in which only the reflected light of the reference light reflected by the first polarization beam splitter is reflected. The third polarizing beam splitter is arranged so that the reflected direction of the incident light reflects only the reflected light from the first polarizing beam splitter of the measurement light. A fourth polarization beam splitter arranged to rotate 45 degrees to the left or right about the optical axis of the incident light with respect to the reference direction to divide the emitted light from the light source into measurement light and reference light. The measurement light reflected by the reflection mirror and transmitted by the λ / 2 plate and the light transmitted by the reference light by the λ / 4 plate are incident on the first polarization beam splitter. The polarization components of the measurement light and the reference light that are orthogonal to each other are polarized and separated into transmitted light and reflected light by the first polarization beam splitter, respectively, and are interference light between the measurement light and the reference light. The second polarizing beam splitter Beauty third polarization beam splitter, and having a photodetector for detecting at least one of the light of the transmitted light or the reflected light.

Further, according to the present invention, light emitted from a light source is branched into measurement light and reference light, and the measurement light is reflected by a reflection mirror fixed to a measurement object, and polarization components of the reference light that are orthogonal to each other. Is polarized and separated into transmitted light and reflected light by the first polarizing beam splitter, respectively, and the amount of displacement of the measurement object is measured based on the optical detection output of the interference light. The polarization separation interferometer-type length measuring device includes: a second polarization beam splitter that polarization-separates the transmitted light of the measurement light and the reflected light of the reference light in the first beam splitter; A third polarization beam splitter that polarization-separates the reflected light of the measurement light and the transmitted light of the reference light in the first beam splitter, and the second polarization beam splitter has a reflection direction of incident light that is First reference light With respect to a reference direction that reflects only the light reflected by the polarizing beam splitter, the optical axis of the incident light is arranged to be rotated 45 degrees to the left or right, and the third polarizing beam splitter is The light source is arranged to be rotated 45 degrees to the left or right around the optical axis of the incident light with respect to a reference direction in which only the reflected light of the measurement light from the first polarization beam splitter is reflected. A non-polarizing beam splitter that branches the output light from the measurement light into the measurement light and the reference light, and the measurement light reflected by the reflection mirror and transmitted through the λ / 4 plate and the reference light, The polarization components of the measurement light and the reference light that are orthogonal to each other are separated into transmitted light and reflected light by the first polarization beam splitter, respectively, and the measurement light and the reference light are separated. Dried with light The output of the second polarizing beam splitter and the third polarizing beam splitter, which are interference lights, is detected by light and the detected output is processed to obtain a displacement amount of the measurement object. And
Further, according to the present invention, the light emitted from the light source is branched into measurement light and reference light, and the light reflected by the reflection mirror fixed to the measurement object and the polarization components of the reference light that are orthogonal to each other. Polarization separation interferometer type length measurement that measures the displacement of the object to be measured based on the optical detection output of the interference light by polarization separation into transmitted light and reflected light by the first polarization beam splitter, respectively. The polarization separation interferometer-type length measuring device includes: a second polarization beam splitter that polarization-separates transmitted light of the measurement light and reflected light of the reference light in the first beam splitter; And a third polarizing beam splitter that polarization-separates the reflected light of the measurement light and the transmitted light of the reference light in one beam splitter, and the second polarizing beam splitter has a reflection direction of incident light that is the reference light The first of light The third polarization beam splitter is arranged to be rotated 45 degrees to the left or right around the optical axis of the incident light with respect to a reference direction that reflects only the reflected light from the light beam splitter. The light source is arranged to be rotated 45 degrees to the left or right around the optical axis of the incident light with respect to a reference direction in which only the reflected light of the measurement light from the first polarization beam splitter is reflected. A fourth polarizing beam splitter that branches the output light from the measurement light into the reference light, the measurement light reflected by the reflection mirror and transmitted through the λ / 2 plate, and the reference light as λ The light transmitted through the / 4 plate is incident on the first polarization beam splitter, and polarized light components of the measurement light and the reference light that are orthogonal to each other are transmitted and reflected by the first polarization beam splitter, respectively. Polarized and separated into light, The measurement object is obtained by optically detecting the outputs of the second polarization beam splitter and the third polarization beam splitter, which are interference lights between the measurement light and the reference light, and processing the detected outputs. It is characterized by obtaining the amount of displacement of an object.

According to the present invention, interference between the measurement light and the reference light from the light obtained by polarization-separating the measurement light and the reference light into transmitted light and reflected light for each of the polarization components orthogonal to each other by the first polarizing beam splitter. In order to extract the light, a λ / 2 plate that has been conventionally rotated by 22.5 degrees with respect to the optical axis before the second and third polarizing beam splitters is not required.
That is, since it is possible to reduce the number of λ / 2 plate components that were required, it is possible to reduce costs. Further, if the second and third polarizing beam splitters are installed in a V-shaped groove in contact with the two output surfaces of the first polarizing beam splitter, the λ / 2 plate, the first, second and third Since the position adjustment with respect to the polarization beam splitter and the adjustment of the rotation angle of the λ / 2 plate are not required, the adjustment process can be simplified and the size can be reduced by reducing the number of parts.

Example 1
FIG. 1 is a diagram showing a configuration of a polarization separation type interferometer according to the first embodiment of the present invention.
The polarization separation type interferometer 100 is used, for example, when measuring the displacement in the optical axis direction of incident light or reflected light in the measurement target 200.
The polarization separation interferometer 100 includes a housing 101 and a light source 102 disposed in the housing 101, a non-polarizing beam splitter 103, a λ / 4 plate 104, a first polarizing beam splitter 105, and a second polarizing beam splitter. 106, a third polarizing beam splitter 107, photodetectors 108 to 111, and the like.
The measurement target 200 is disposed at a position away from the polarization separation type interferometer 100, and a reflection mirror 201 is installed on the measurement target 200.

As the light source 102, for example, a laser light source with good coherence is used. In order to ensure stable measurement accuracy with high resolution, a helium neon laser with a stabilized oscillation frequency is suitable.
The non-polarizing beam splitter 103 branches at the same light intensity in two directions without depending on the polarization state of incident light.
The reflection mirror 201 is composed of a folding mirror having two reflection portions with an opening angle of 90 degrees, and emits reflected light in a direction parallel to and opposite to the incident direction. The reflection mirror 201 may be a functionally equivalent corner prism or the like.
The λ / 4 plate 104 converts linearly polarized light into circularly polarized light. That is, the light transmitted through the λ / 4 plate 104 has a phase difference of 90 degrees (π / 2) between polarization components orthogonal to each other.
The first, second, and third polarization beam splitters 105, 106, and 107 branch into an H-polarization component and a V-polarization component that are orthogonal to each other. The polarization beam splitters 105, 106, and 107 transmit the H polarization component and reflect the V polarization component. In FIG. 1, a polarizing beam splitter 105 shows a shape of one face of a regular cube viewed from directly above, and polarizing beam splitters 106 and 107 show a shape viewed from a direction facing one side between two adjacent faces of the regular cube. .
The photodetectors 108 to 111 photoelectrically convert incident light and use a photodiode (PD) or the like. In FIG. 1, photodetectors 108 and 110 show a shape of a cylindrical photodetector viewed from the lateral direction, and photodetectors 109 and 111 show a shape seen from an upper direction of 45 degrees.

Next, the operation of the polarization separation type interferometer 100 in the first embodiment will be described with reference to FIG.
The light L ₁ emitted from the light source 102 is arranged at 45 degrees linearly polarized light with respect to the reflection surface of the non-polarizing beam splitter 103. In this state, it consists of an H-polarized component (L _1H ) and a V-polarized component (L _1V ) that are equal in amplitude and orthogonal to each other (Formula 1 in FIG. 3).
Here, E ₁ in FIG. 3 is the electric field intensity of light, and ω is the angular frequency of light.
Light L1 is equal branch to the transmitted component L ₂ by the non-polarizing beam splitter 103 and the reflection component L _4. Each of the branched components is 45-degree linearly polarized light, and is composed of an H-polarized component and a V-polarized component that are equal in amplitude and orthogonal to each other. Since the beam splitter power of light bisects (1/2), the field strength E ₂ becomes as Equation 2 in FIG.

Light _{L 2} passing through the non-polarizing beam splitter 103 is used as a measuring light reflected by the reflection mirror 201, and enters the lambda / 4 plate 104 (the formula 3). The measurement light L ₂ is converted from 45-degree linearly polarized light into circularly polarized light L ₃ by a λ / 4 plate, and is incident on the first polarization beam splitter 105 (Formula 4).
On the other hand, the light L ₄ reflected by the non-polarizing beam splitter 103 is incident on the first polarizing beam splitter 105 as reference light (Formula 5).
Here, the H-polarized component of the light L ₄ L _4H and V-polarized component L _4V is in Sin is because light reflected by the non-polarizing beam splitter 103 is added phase shift of (- [pi] / 2) .
In addition, the phase terms Δθ of Cos and Sin in Expression 3 and Expression 4 are the same as the combining point B of the first polarization beam splitter 105 from the branch point A of the non-polarization beam splitter 103 via the reflection mirror 201. And the phase difference (Δθ) due to the difference between the optical path length between the point A and the optical path length from the point A to the point B. Therefore, in Equation 5 representing the reference light, the phase term is set to zero.

The H polarization component L _3H of the measurement light L ₃ incident on the first polarization beam splitter 105 is transmitted to the second polarization beam splitter 106 side, and the V polarization component L _3V is (− Reflected with a phase shift of π / 2).
On the other hand, the H polarization component L _4H of the reference light L ₄ incident on the first polarization beam splitter 105 is transmitted to the third polarization beam splitter 107 side, and the V polarization component L _4V is transmitted to the second polarization beam splitter 106 side. Reflected with a phase shift of (−π / 2).
That is, the incident light _{L 5} of the second beam splitter 106 is made of a V-polarized light component is phase shift applied in the H-polarized component _{L 3H} of the measuring light, the reference light _{L 4V (-π} / 2) is there. The incident light L ₆ of the third beam splitter 107 is composed of a V-polarized component obtained by adding a phase shift of (−π / 2) to the measuring light L _3V and an H-polarized component L _{4H of the} reference light ( Equations 7 and 8).

Here, since the two outgoing lights L _5H and L _5V of the first beam splitter 105 are an H-polarized component and a V-polarized component orthogonal to each other, the second beam splitter 106 is set to either the H-polarized component or the V-polarized component. In the case where it is arranged in a direction parallel to a normal paper surface that transmits only one of them, each polarization component is simply branched and an interference signal cannot be obtained.
The same applies to the two outgoing lights L _6H and L _6V of the first beam splitter 105.

Therefore, in the present embodiment, the second beam splitter 106 is configured to reflect only the V-polarized light component, that is, in FIGS. 1 and 2, the reflected optical axis is parallel to the paper surface and from the vertical direction to the paper surface. Arranged in a direction rotated 45 degrees around the incident optical axis of the light L5 in the left-right direction, and the third beam splitter 107 reflects only the V-polarized component, that is, the reflected optical axis is parallel to the paper surface and left-right direction. Are arranged in a direction rotated 45 degrees around the incident optical axis of the light L6 in the vertical direction parallel to the paper surface.
4 and 5 show the arrangement directions of the second and third polarizing beam splitters. 4 is a view of the second polarizing beam splitter 106 of FIG. 2 as viewed from the direction opposite to the traveling direction of incident light (the right direction of the drawing), and FIG. 5 is incident on the third polarizing beam splitter 107 of FIG. It is the figure seen from the reverse direction (upward direction of drawing) with the advancing direction of light.
Therefore, when showing the direction of the optical axis of the light emitted from the light source 102 at O1, the optical axis O2, O3 of L ₅ and L ₆ are perpendicular to the paper surface and toward the surface from the back surface.
Here, the circular display of the photodetectors 108 and 110 represents the shape of the cylindrical photodetector viewed from behind, and the square display of the photodetectors 109 and 111 represents the shape of the photodetector viewed from the side. Yes.

That is, as shown in FIG. 4, the second polarization beam splitter 106 has a reference surface that reflects only the reflected light of the reference light L4 from the first polarization beam splitter 105 (imaginary line in FIG. 4). (Shown in (b)) with respect to the direction rotated 45 degrees around the incident optical axis O2.
With this arrangement, the reference light component and the measurement light component of the outgoing light L ₅ of the first polarization beam splitter 105 is incident at an angle of 45 degrees with respect to the second polarizing beam splitter 106.
Here, the measurement light component and the reference light component _{L 5} of the second polarization beam splitter 106 is incident after rotating 45 °, H-polarized component _{(L 5MH,} L _5RH) and V-polarization component _{(L 5MV,} L _5RV) Are disassembled and displayed (Formulas 9 and 10). Thus, component transmitted to the optical axis O2 of the second polarizing beam splitter 106 is _{L 5MH,} the _{L 5 RH,} component reflected to the optical axis O4 side becomes _L 5 _{MV, L 5RV.}
The subscript M of each polarization component represents the measurement light component, R represents the reference light component, and the phase shift of each component after 45 ° rotation was based on the H polarization component (L _5MH ) of the measurement light.

Similarly, as shown in FIG. 5, the third polarization beam splitter 107 has a reference surface (imagine in FIG. 5) whose reflection surface reflects only the reflected light of the measurement light L3 from the first polarization beam splitter 105. With respect to the incident optical axis O3.
By arranging in this way, the reference light component and the measurement light component of the outgoing light L ₆ of the first polarizing beam splitter 105 are incident on the third polarizing beam splitter 107 at an angle of 45 degrees.
Here, the measurement light component and the reference light component _{L 6} of the third polarization beam splitter 107 is incident after rotating 45 °, H-polarized component _{(L 6RH,} L _6MH) and V-polarization component _{(L 6RV,} L _6MV) Are disassembled and displayed (Formulas 11 and 12). Thus, component transmitted to the optical axis O3 of the third polarization beam splitter 107 is _{L 6RH,} the _{L 6MH,} component reflected to the optical axis O5 side becomes _{L 6RV, L 6MV.}
The phase shift of each component after rotation by 45 degrees is based on the H polarization component (L _6RH ) of the reference light, and E _{3 in} Equations 7 to 12 is equally divided by the beam splitter as E ₂ in Equation 2. (Formula 6).

By rotating the second and third polarizing beam splitters 106 and 107 by 45 degrees, the second polarizing beam splitter 106 transmits the H-polarized component (L _7M , L _7R ) of the incident light component (same formula) 14, 15), the light direction becomes the light L ₇ that can be detected by the interference effect because the polarization directions coincide (formula 16), and reflects the V-polarized components (L _8M , L _8R ) (formulas 17 and 18). ) And light L ₈ in the same manner (Formula 19).
Similarly, the third polarization beam splitter 107 transmits the H polarization component (L _9M , L _9R ) of the incident light component (Formulas 20 and 21) and reflects the V polarization component (L _10M , L _10R ). (Formulas 23 and 24), the polarization directions coincide and L ₉ and L ₁₀ that can be detected by the interference effect are obtained (Formulas 22 and 25).
Here, E ₄ in Expressions 14 to 25 is obtained by dividing the beam splitter equally by E ₂ in Expression 2 (Expression 13).

The interference light signals L ₇ and L ₈ incident on the photodetectors 108 and 109 are square-detected by the photodetector to become output signals 301 and 302 (Equations 26 and 27 in FIG. 6). Here, k in Equations 26 to 28 is a photoelectric conversion coefficient, and D _7M , D _7R , D _8M , and D _8R are direct detection components of the measurement light and the reference light that have passed through the second polarization beam splitter 106. The amplitudes were all equal (Formula 28).
The output signals 301 and 302 of the photodetectors 108 and 109 are input to the subtraction circuit 305, and a signal 307 of these differences is obtained (formula 29). That is, a component of Cos (Δθ) resulting from the phase difference between the measurement light of the interference light L ₅ and the reference light is obtained. The coefficient Io in Expression 29 represents a current component proportional to the output power Po of the light source 102 as shown in Expression 30, and the term Cos (2ωt + Δθ) is omitted because the frequency of light is twice.
Similarly, output signals 303 and 304 of the photodetectors 110 and 111 are input to a subtraction circuit 306, and a signal 308 of these differences is obtained. That is, a component of Sin (Δθ) resulting from the phase difference between the measurement light of the interference light L ₆ and the reference light is obtained (Formulas 31 to 34).
From the output signals of these two subtraction circuits 305 and 306, for example, the displacement amount of the measuring object 200 is calculated by the arithmetic processing in the arithmetic circuit 309.
This result is exactly the same as the conventional configuration using two λ / 2 plates.

In the present embodiment, processing for subtracting the detection signals of the H polarization components L ₇ and L _{8 and} the detection signals of the V polarization components L ₉ and L ₁₀ of the interference light is performed. This is to suppress the amplitude noise of the signal and operate with the best signal-to-noise ratio (S / N). In order to simplify the configuration, one of the H polarization components L ₇ and L ₈ of the interference light and the detection signal of one of the V polarization components L ₉ and L ₁₀ are directly calculated. A configuration in which the signal is input to the circuit 309 may be used.

As described above, according to this embodiment, the second polarizing beam splitter 106, the reflecting surface is, the reference position that reflects only light reflected by the first polarization beam splitter 105 of the reference light L ₄ in contrast, towards rotated 45 degrees around the incident light axis O2 which is incident on the reflecting surface direction is arranged, also, the third polarization beam splitter 107, is the reflecting surface, of the measurement light L ₃ third With respect to the reference position that reflects only the reflected light from one polarization beam splitter 105, the measurement light and the measurement light are arranged in a direction rotated 45 degrees around the incident optical axis O3 incident on the reflecting surface. An interference signal of reference light can be obtained.
That is, in the past, a λ / 2 plate was placed in front of the second and third polarization beam splitters in order to obtain an interference signal between the measurement light and the reference light, but the two λ / 2 plates were reduced. It becomes possible to do. As a result, the cost as an interferometer can be reduced, and if the second and third polarizing beam splitters are installed in V-shaped grooves in contact with the two output surfaces of the first polarizing beam splitter, λ / The adjustment process can be simplified by eliminating the need for position adjustment with respect to the two plates, the first, second, and third polarizing beam splitters, and the adjustment of the rotation angle of the λ / 2 plate. Can be realized.

  In the present embodiment, first, the measurement light and the reference light branched by the non-polarizing beam splitter, reflected by the measurement object, and transmitted through the λ / 4 plate, and the reference light are converted into the first polarized light. Although the polarization separation is performed by the beam splitter, the configuration of the non-polarization beam splitter, the polarization beam splitter, the λ / 4 plate, and the like is not limited to this embodiment. For example, the λ / 4 plate disposed in the optical path of the measurement light may be disposed in the optical path of the reference light between the non-polarization beam splitter that separates the light source into the measurement light and the reference light and the first polarization beam splitter. . Further, the incident optical axis from the light source to the non-polarizing beam splitter may be the optical axis of the reference light. Further, the measurement light obtained by separating the laser emission light by the fourth polarizing beam splitter is reflected on the measurement object, transmitted through the λ / 2 plate, and the reference light transmitted through the λ / 4 plate is used as the first polarized beam. Different configurations such as a configuration in which polarization is separated by a splitter may be used.

  In the present embodiment, a reflection mirror is arranged on the measurement target, and the amount of displacement of the measurement target is measured by reflecting the measurement light by the reflection mirror. However, the application of the polarization separation type interferometer of the present invention is used. However, the present invention is not limited to this, and is used for a wide variety of applications such as measurement of a change in refractive index of a measurement object.

It is a block diagram which shows the structure of the polarization separation type interferometer in embodiment of this invention. It is explanatory drawing which shows the optical path of the polarization separation type interferometer in embodiment of this invention. It is a figure which shows the numerical formula of the polarization component of each optical path to the 1st polarization beam splitter output of the polarization-separation type interferometer in the embodiment of the present invention. It is explanatory drawing which shows the arrangement direction of the 2nd polarizing beam splitter in embodiment of this invention. It is explanatory drawing which shows the arrangement direction of the 3rd polarizing beam splitter in embodiment of this invention. It is a figure which shows the numerical formula of the polarization component of each optical path after the 1st polarizing beam splitter output of the polarization-separation type interferometer in an embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 102 ... Light source, 103 ... Non-polarization beam splitter, 104 ... (lambda) / 4 board, 105-107 ... Polarization beam splitter, 108-111 ... Photo detector, 201 ... Reflection mirror, 300 ... Arithmetic processing Department.

Claims (6)

The light emitted from the light source is branched into measurement light and reference light, and polarized light components of the measurement light reflected from the reflection mirror and the reference light that are orthogonal to each other are transmitted and reflected by the first polarization beam splitter, respectively. A polarization-separation type interferometer that separates and interferes with light to detect the interference light,
The polarization separation type interferometer includes a second polarization beam splitter that polarization-separates the transmitted light of the measurement light and the reflected light of the reference light in the first beam splitter, and the measurement light in the first beam splitter. And a third polarization beam splitter for polarizing and separating the reflected light of the reference light and the transmitted light of the reference light,
The second polarizing beam splitter is configured such that a reflection direction of incident light is either left or right around the optical axis of the incident light with respect to a reference direction that reflects only the reflected light of the reference light from the first polarizing beam splitter. The crab is rotated 45 degrees,
The third polarization beam splitter is configured so that the incident light is reflected in the left or right direction around the optical axis of the incident light with respect to a reference direction in which only the reflected light of the measurement light reflected by the first polarization beam splitter is reflected. The crab is rotated 45 degrees,
A non-polarizing beam splitter that branches the light emitted from the light source into measurement light and reference light;
The measurement light reflected by the reflection mirror and transmitted through the λ / 4 plate and the reference light are incident on the first polarization beam splitter, and the measurement light and the reference light are orthogonally polarized. The components are polarized and separated into transmitted light and reflected light by the first polarization beam splitter, respectively.
A photodetector for detecting at least one of transmitted light and reflected light of the second polarizing beam splitter and the third polarizing beam splitter, which is interference light between the measurement light and the reference light; ,
A polarization separation type interferometer characterized by the above.   The light emitted from the light source is branched into measurement light and reference light, and polarized light components of the measurement light reflected from the reflection mirror and the reference light that are orthogonal to each other are transmitted and reflected by the first polarization beam splitter, respectively. A polarization-separation type interferometer that separates and interferes with light to detect the interference light,
  The polarization separation type interferometer includes a second polarization beam splitter that polarization-separates the transmitted light of the measurement light and the reflected light of the reference light in the first beam splitter, and the measurement light in the first beam splitter. And a third polarization beam splitter for polarizing and separating the reflected light of the reference light and the transmitted light of the reference light,
  The second polarizing beam splitter is configured such that a reflection direction of incident light is either left or right around the optical axis of the incident light with respect to a reference direction that reflects only the reflected light of the reference light from the first polarizing beam splitter. The crab is rotated 45 degrees,
  The third polarization beam splitter is configured so that the incident light is reflected in the left or right direction around the optical axis of the incident light with respect to a reference direction in which only the reflected light of the measurement light reflected by the first polarization beam splitter is reflected. The crab is rotated 45 degrees,
  A fourth polarization beam splitter for branching the emitted light from the light source into measurement light and reference light;
  The measurement light reflected by the reflection mirror and transmitted by the λ / 2 plate and the light transmitted by the reference light by the λ / 4 plate are incident on the first polarization beam splitter, and The polarization components of the measurement light and the reference light that are orthogonal to each other are polarized and separated into transmitted light and reflected light by the first polarization beam splitter, respectively.
  A photodetector for detecting at least one of transmitted light and reflected light of the second polarizing beam splitter and the third polarizing beam splitter, which is interference light between the measurement light and the reference light; ,
  A polarization separation type interferometer characterized by the above. The light emitted from the light source is branched into measurement light and reference light, and the light reflected by the reflection mirror fixed to the measurement object and the polarization components orthogonal to each other of the reference light are converted into the first polarized light. A polarization separation interferometer type length measuring device that causes polarized light to be separated into transmitted light and reflected light by a beam splitter, interferes with each other, and measures the amount of displacement of the measurement object based on the optical detection output of the interference light,
The polarization separation interferometer type length measuring device includes: a second polarization beam splitter that polarizes and separates the transmitted light of the measurement light and the reflected light of the reference light in the first beam splitter; and the first beam splitter. A third polarization beam splitter that polarization-separates the reflected light of the measurement light and the transmitted light of the reference light;
The second polarizing beam splitter is configured such that a reflection direction of incident light is either left or right around the optical axis of the incident light with respect to a reference direction that reflects only the reflected light of the reference light from the first polarizing beam splitter. The crab is rotated 45 degrees,
The third polarization beam splitter is configured so that the incident light is reflected in the left or right direction around the optical axis of the incident light with respect to a reference direction in which only the reflected light of the measurement light reflected by the first polarization beam splitter is reflected. The crab is rotated 45 degrees,
A non-polarizing beam splitter that branches the light emitted from the light source into measurement light and reference light;
The measurement light reflected by the reflection mirror and transmitted through the λ / 4 plate and the reference light are incident on the first polarization beam splitter, and the measurement light and the reference light are orthogonally polarized. The components are polarized and separated into transmitted light and reflected light by the first polarization beam splitter, respectively.
By detecting the outputs of the second polarization beam splitter and the third polarization beam splitter, which are interference lights between the measurement light and the reference light, and calculating the detection outputs, the measurement object Get the displacement of the object,
A polarization separation interferometer type length measuring device characterized by the above.   The light emitted from the light source is branched into measurement light and reference light, and the light reflected by the reflection mirror fixed to the measurement object and the polarization components orthogonal to each other of the reference light are converted into the first polarized light. A polarization separation interferometer type length measuring device that causes polarized light to be separated into transmitted light and reflected light by a beam splitter, interferes with each other, and measures the amount of displacement of the measurement object based on the optical detection output of the interference light,
  The polarization separation interferometer type length measuring device includes: a second polarization beam splitter that polarizes and separates the transmitted light of the measurement light and the reflected light of the reference light in the first beam splitter; and the first beam splitter. A third polarization beam splitter that polarization-separates the reflected light of the measurement light and the transmitted light of the reference light;
  The second polarizing beam splitter is configured such that a reflection direction of incident light is either left or right around the optical axis of the incident light with respect to a reference direction that reflects only the reflected light of the reference light from the first polarizing beam splitter. The crab is rotated 45 degrees,
  The third polarization beam splitter is configured so that the incident light is reflected in the left or right direction around the optical axis of the incident light with respect to a reference direction in which only the reflected light of the measurement light reflected by the first polarization beam splitter is reflected. The crab is rotated 45 degrees,
  A fourth polarization beam splitter for branching the emitted light from the light source into measurement light and reference light;
  The measurement light reflected by the reflection mirror and transmitted by the λ / 2 plate and the light transmitted by the reference light by the λ / 4 plate are incident on the first polarization beam splitter, and The polarization components of the measurement light and the reference light that are orthogonal to each other are polarized and separated into transmitted light and reflected light by the first polarization beam splitter, respectively.
  By detecting the outputs of the second polarization beam splitter and the third polarization beam splitter, which are interference lights between the measurement light and the reference light, and calculating the detection outputs, the measurement object Get the displacement of the object,
  A polarization separation interferometer type length measuring device characterized by the above. The light source is a laser light source, which emits 45-degree linearly polarized light composed of an H-polarized component and a V-polarized component having equal amplitude and orthogonal to each other.
A polarization separation interferometer according to claim 1, a polarization separation interferometer according to claim 2, a polarization separation interferometer type length measuring device according to claim 3, or a polarization separation interferometer according to claim 4. Type length measuring instrument . The reflection surface of the first polarization beam splitter transmits only the H polarization component of the measurement light in the direction of the second polarization beam splitter and only the V polarization component in the direction of the third polarization beam splitter. And only the H-polarized component of the reference light is transmitted in the direction of the third polarizing beam splitter, and only the V-polarized component is disposed in the direction of reflecting toward the second polarizing beam splitter. The
A polarization separation interferometer according to claim 1, a polarization separation interferometer according to claim 2, a polarization separation interferometer type length measuring device according to claim 3, or a polarization separation interferometer according to claim 4. Type length measuring instrument .

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