JPH1073409A - Interference measuring instrument using light wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interference measuring instrument using light wave which can correct a distance measuring error caused by the refractive index fluctuation of an optical path with high accuracy by suppressing the deterioration of the measuring accuracy caused by unnecessary measurement of refractive index fluctuation and the lack of necessary measurement of the fluctuation. SOLUTION: First light for measuring distance arriving through a measuring optical path and a reference optical path is separated from second and third light rays after the first light is transmitted through a first interference light generating system (7-9) and a second interference light generating system (15-18) for measuring refractive index fluctuation and interferes with the second and third light rays and interferes through a third interference light generation system (12, 21). When an interference measuring instrument is constituted in such a way, the distance measuring optical path for which refractive index fluctuation is not measured although the measurement of the fluctuation is required can be made shorter in length and a distance nonmeasuring optical path for which refractive index fluctuation is measured although the measurement of the fluctuation is not required does not exist at all.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light wave interference measuring device, and more particularly to a light wave interference measuring device for performing highly accurate displacement measurement.

[0002]

2. Description of the Related Art FIG. 11 is a diagram schematically showing a configuration of a conventional light wave interference measuring device. The light wave interference measurement device of FIG. 11 measures the displacement amount D of the movable mirror 6 in the optical axis direction (the direction of the arrow in the figure). The light source 1 emits light including light having a frequency ω ₁ and light having a frequency ω ₁ ′ (ω ₁ ′ = ω ₁ + Δω ₁ ). The two lights have slightly different frequencies from each other,
The polarization directions are orthogonal to each other.

[0003] The two light beams having different frequencies are incident on a polarization beam splitter 4 such as a polarization beam splitter via a light beam separation device 2 such as a beam splitter, where the light beam having the frequency ω ₁ 'and the light beam having the frequency ω ₁ are emitted. And separated. The light having the frequency ω ₁ ′ becomes reference light, is reflected by the fixed mirror 5, and returns to the polarization splitting element 4 again. Also, the light of frequency ω ₁ becomes the measuring light,
After being reflected by the movable mirror 6, the light returns to the polarization splitting element 4 again.

The measuring light and the reference light returning to the polarization beam splitter 4 are emitted from the polarization beam splitter 4 along the same optical path. The measurement light and the reference light emitted from the polarization splitting element 4 along the same optical path interfere with each other via the polarizing plate 21. The polarizing plate 21 is, specifically, a polarizing element that is disposed at an angle of 45 ° with respect to the polarization direction of the reference light and the polarization direction of the measurement light. The interference light generated via the polarizing plate 21 is photoelectrically converted by the light receiving element 22 and is measured, and the measurement beat signal (frequency Δ
ω ₁ ) 101 is input to the phase meter 105.

On the other hand, a part of the light of two different frequencies emitted from the light source 1 is reflected by the light separating element 2 and
3 via The interference light generated via the polarizing plate 23 is photoelectrically converted by the light receiving element 24 and input to the phase meter 105 as a reference beat signal (frequency Δω ₁ ) 100. Note that the polarizing plate 23 includes two different frequencies of light (light having a frequency ω ₁ ′ and frequency ω ₁₎ as in the case of the polarizing plate 21.
Is a polarizing element that interferes with the light.

The phase meter 105 obtains a displacement D (ω ₁ ) of the movable mirror 6 by measuring a phase change of the measurement beat signal 101 with respect to the reference beat signal 100, and uses the displacement information as a signal 107 as an arithmetic unit 108. Output to

In order to accurately (highly) measure the length by interference of light waves as shown in FIG. 11, fluctuations in the refractive index of air (or other gases) in the optical path cannot be ignored. Therefore, the conventional light wave interference measuring device is shown in FIG.
As shown in (1), an air sensor 532 is provided as a means for correcting a length measurement error caused by a change in the refractive index of air in the measurement optical path. That is, the temperature, pressure, and humidity of the atmosphere in the measurement optical path are measured using the air sensor 532, and the wavelength of light is corrected based on the measurement result, thereby correcting a length measurement error caused by a change in the refractive index of air. doing.

That is, D is the true displacement of the movable mirror,
Assuming that the refractive index of air is n and n is spatially uniform, the displacement D (ω ₁ ) measured by the light wave interference measurement device
Is

D (ω ₁ ) = nD (1)

Therefore, the refractive index n can be obtained by measuring the temperature, pressure, and humidity of the air along the measurement optical path with the air sensor 532. That is, the arithmetic unit 108 outputs the signal 1 of the displacement D (ω ₁ ) from the phase meter 105.
07, the temperature, pressure, and humidity measurement signals 106 from the air sensor 532 and the arithmetic expression shown in Expression (2).
The true displacement D of the movable mirror 6 can be obtained.

[0010]

As described above, in the prior art, the air temperature,
Pressure and humidity are detected by an air sensor. For this reason, accurate correction is possible when the refractive index of air uniformly fluctuates along the measurement optical path and the reference optical path, but the refractive index of air locally changes on the measurement optical path and the reference optical path. However, there is a disadvantage that the length measurement error caused by the change in the refractive index of air cannot be accurately corrected.

Therefore, the present inventors have filed Japanese Patent Application No. 7-609.
In the specification and drawings of Japanese Patent Application No. 69 and Japanese Patent Application No. 7-64537, a light wave interferometer capable of correcting a length measurement error caused by a change in refractive index of air using light of two different frequencies is proposed. doing. In addition, Japanese Patent Application No. 7-60
The light wave interference measurement device disclosed in the specification and the drawings of Japanese Patent Application No. 969 and Japanese Patent Application No. 7-64537 has not been disclosed at the time of filing the present application, and does not belong to the prior art of the present application.

FIG. 10 is a diagram schematically showing the configuration of an optical interference measuring apparatus disclosed in the specifications and drawings of Japanese Patent Application Nos. 7-60969 and 7-64537. In addition,
In FIG. 10, the same components as those of the conventional optical interference measuring apparatus in FIG. 11 are denoted by the same reference numerals. Hereinafter, the device of FIG. 10 will be described focusing on the difference from the device of FIG. 11, and redundant description will be omitted.

In the optical interference measuring apparatus shown in FIG. 10, two different frequencies ω ₂ (fundamental waves) are provided on the same optical path as the light emitted from the length measuring light source 1 (hereinafter, referred to as “coaxially”).
And ω ₃ (harmonic) laser light are coupled. Thus, the refractive index fluctuation of air (or other gas or the like) in the optical path of the length measuring interferometer can be obtained by using the two different frequencies of laser light.

In the optical interference measuring apparatus shown in FIG.
There emits the light of the frequency omega ₂ of the light and the frequency omega ₃ coaxially. The polarization directions of the light having the frequency ω _{2 and} the light having the frequency ω ₃ are at 45 ° to the polarization direction of the light emitted from the length measuring light source 1. Light with the frequency omega ₂ of the light and the frequency omega ₃ binds to e.g. dichroic from long light source 1 measured by the frequency coupling element 3 consisting of dichroic mirror of the injection frequency omega ₁ light coaxially. The coaxially coupled light enters the polarization beam splitter 4 via the same optical path.

The light of frequency ω _{2 and} the light of frequency ω ₃ are
The light is split by the polarization splitting element 4 into light reflected on the fixed mirror 5 (reference light) and light transmitted on the movable mirror 6 (measurement light). Between the reference light and the measurement light, its polarization direction are orthogonal to each other, and includes both the frequency omega ₂ of the light and the frequency omega ₃ of the light respectively. The reference light reflected by the polarization separation element 4 is reflected by a fixed mirror 5 made of, for example, a corner cube, and then returns to the polarization separation element 4 again. On the other hand, the measurement light transmitted through the polarization separation element 4 is reflected by the movable mirror 6 formed of, for example, a corner cube, and then returns to the polarization separation element 4 again. Here, the corner cube forming the fixed mirror 5 and the corner cube forming the moving mirror 6 are arranged so that the incident point of the reference light and the incident point of the measurement light incident on the polarization splitting element 4 do not substantially overlap. Have been.

Thus, the reference optical path (the optical path through which the reference light passes)
The light of frequency ω _{2 and} the light of frequency ω ₃ emitted from the polarization splitting element 4 via the optical path and the frequency ω ₂ emitted from the polarization splitting element 4 via the measurement optical path (the optical path through which the measurement light passes)
And the light of the frequency ω ₃ along the optical paths different from each other (spatially separated from each other).
Incident at 0. Frequency separating device 500, for example, a dichroic mirror, has the property of transmitting only light of the frequency omega ₁ near and reflects light of other frequencies. Accordingly, the light of the light and the frequency omega ₃ frequency omega ₂ by the action of the frequency separation device 500 is separated from light (frequency omega ₁ near the light) from the long light source 1 measurement.

The frequency is reflected by the separation element 500 frequency omega ₂ of the light and the frequency omega ₃ of light, that the light of the frequency omega ₂ of the light and the frequency omega ₃ through the reference optical path, the frequency omega ₂ through the measurement light path And the light of the frequency ω ₃ along the optical paths different from each other, the polarization rotators 507 and 51
5 and refraction optical elements 508 and 516, and are incident on frequency conversion elements 509 and 517, respectively. In the frequency converting element 509 and 517, are harmonic conversion to a higher frequency omega ₃ optical low frequency omega ₂ of the light frequency of the frequency, the light of the higher frequency omega ₃ frequency is transmitted as it is. In this manner, the light of frequency ω ₃ whose frequency has been converted by the frequency conversion elements 509 and 517 interferes with the light of frequency ω ₃ emitted from the light source unit 50 and passing through a predetermined optical path. The interference light generated via the frequency conversion elements 509 and 517 is converted into parallel light by the refractive optical elements 510 and 518, and then photoelectrically converted by the light receiving elements 551 and 552, respectively.

Unless special consideration is given, the polarization direction of the light of frequency ω ₃ that has been frequency-converted by the frequency conversion elements 509 and 517 is the polarization direction of the light of frequency ω ₃ incident on the frequency conversion elements 509 and 517. And different. Therefore, as described above, the polarization rotation device 507 and 515 inserted in the optical path is varied independently and polarization orientation of the frequency omega ₃ light polarizing direction and the frequency omega ₂ of the light for example, a plurality of wave plates ing. This polarization rotation device 50
By the action of 7 and 515, to match the polarization direction of light with the frequency converted frequency omega _3, and a polarization direction of light with the frequency omega ₃ entering the frequency conversion element 509 and 517 by the frequency converting element 509 and 517 Interference light can be generated.

The refractive optical elements 508 and 516
Is an optical element inserted in the optical path to increase the conversion efficiency of frequency conversion, and has a function of condensing reference light and measurement light on the frequency conversion elements 509 and 517. This is because the conversion efficiency of the frequency conversion element 509 and 517 is proportional to the square of the light intensity per unit area of the light (i.e. the frequency omega ₂ of the light) to be frequency-converted.

[0020] Interference signals by a the light receiving element 551, the frequency omega ₂ through the reference optical path of the light and the frequency omega ₃ Light 102
Is generated. Further, the light receiving element 552, the interference signal 103 due to the light of the frequency omega ₂ of the light and the frequency omega ₃ through the measurement optical path is produced. The interference signal 102 from the light receiving element 551 and the interference signal 103 from the light receiving element 552 are
Both are supplied to the phase meter 104. In the phase meter 104,
Based on the phase difference between the interference signal 102 caused by the light having the frequency ω _{2 and} the light having the frequency ω ₃ via the reference optical path and the interference signal 103 caused by the light having the frequency ω _{2 and} the light having the frequency ω ₃ via the measurement optical path. Te, the optical path length variation with respect to the frequency omega ₃ light D (omega
{D (ω ₃ ) −D (ω ₂ )}, which is the difference between ₃ ) and the optical path length change D (ω ₂ ) for the light of frequency ω ₂ . The signal 106 related to {D (ω ₃ ) −D (ω ₂ )} obtained by the phase meter 104 is supplied to the arithmetic unit 108.

The optical interference measurement apparatus shown in FIG. 10 also includes a light source 1 for supplying light for measuring the displacement of the movable mirror 6 in the optical axis direction (the direction of the arrow in the figure). The light source 1 emits light including light having a frequency ω ₁ and light having a frequency ω ₁ ′ (ω ₁ ′ = ω ₁ + Δω ₁ ). The two lights have slightly different frequencies from each other and polarization directions orthogonal to each other. This 2
Light having two different frequencies enters the polarization splitter 4 via the light splitter 2 and is separated into light having a frequency ω ₁ ′ and light having a frequency ω ₁ . The light having the frequency ω ₁ ′ becomes reference light, is reflected by the fixed mirror 5, and returns to the polarization splitting element 4 again. Also,
The light having the frequency ω ₁ becomes measurement light, is reflected by the movable mirror 6, and returns to the polarization separation element 4 again. Thus, the frequency ω
₁ reference light 'along the same optical path as the reference beam composed of the frequency omega ₂ of the light and the frequency omega ₃ light, the frequency omega ₁ of the measuring light measurement light comprising frequency omega ₂ of the light and the frequency omega ₃ light The light returns to the polarization splitting element 4 along the same optical path as that described above. As described above, the incident point of the reference light and the incident point of the measurement light that re-enter the polarization splitting element 4 are configured not to substantially coincide with each other.

[0022] Thus, the light emitted frequency omega ₁ 'from the polarization separating element 4 through the reference optical path, and the measurement optical path of the polarized light separating element 4 frequencies omega ₁ emitted from over the optical, different optical paths from each other Along the frequency separation element 500. As described above, the frequency separation element 500 has the property of transmitting only light of the frequency omega ₁ near and reflects light of other frequencies. Therefore, the reference light having the frequency ω ₁ ′ and the measurement light having the frequency ω ₁ pass through the frequency separation element 500. The reference light having the frequency ω ₁ ′ transmitted through the frequency separation element 500 is reflected by the reflecting mirror 501, and
The measurement light having the frequency ω ₁ transmitted through 00 directly enters the polarization coupling element 502 such as a polarization beam splitter.

The reference light having the frequency ω ₁ ′ and the measurement light having the frequency ω ₁ which are coaxially coupled via the polarization coupling element 502 interfere with each other via the polarizing plate 21. The polarizing plate 21 is composed of, for example, polarizing elements that are arranged at an angle of 45 ° with respect to the polarization direction of the reference light having the frequency ω ₁ ′ and the polarization direction of the measurement light having the frequency ω ₁ . The interference light generated via the polarizing plate 21 is photoelectrically converted by the light receiving element 22. Thus, the light receiving element 22 supplies the measurement beat signal (frequency Δω ₁ ) 101 based on the interference light to the phase meter 105. On the other hand, a part of the light of two different frequencies (light of frequency ω ₁ and light of frequency ω ₁ ′) emitted from the light source 1 is reflected by the light separating element 2 and interferes via the polarizing plate 23. The interference light generated via the polarizing plate 23 is photoelectrically converted by the light receiving element 24, and the reference beat signal (frequency Δω ₁ )
100 is input to the phase meter 105.

In the phase meter 105, the reference beat signal 100
, The displacement D (ω ₁ ) of the movable mirror 6 without considering the influence of the refractive index fluctuation is obtained, and a signal 107 relating to the displacement D (ω ₁ ) is obtained. It is supplied to the arithmetic unit 108. Arithmetic unit 1
In step 08, the displacement D (ω ₁ ) of the movable mirror 6 measured by the length measuring interferometer using the light source 1 is corrected, and the true displacement (geometric distance) D of the movable mirror is obtained.

Hereinafter, the correction from the displacement D (ω ₁ ) of the movable mirror 6 to the true displacement (geometric distance) D will be described. The optical path length changes D (ω ₁ ), D (ω ₂ ) and D (ω ₃ ) for light of frequencies ω ₁ , ω ₂ and frequency ω ₃ are:
These are represented by the following equations (3) to (5), respectively.

D (ω ₁ ) = {1 + NF (ω ₁ )} × D (3)

D (ω ₂ ) = {1 + NF (ω ₂ )} × D (4)

D (ω ₃ ) = {1 + NF (ω ₃ )} × D (5)

Here, D is a geometric distance, and N is the density of air. F (ω) is a function that depends only on the frequency ω of the light without depending on the density of the air if the composition ratio of the air is unchanged. Equations (3) to (5) above
Thus, the geometric distance D is given by the following equation (6).

D = D (ω ₁ ) −A ｛D (ω ₃ ) −D (ω ₂ )｝ (6) where A = F (ω ₁ ) / ｛F (ω ₃ ) −F (ω ₂ )｝.

D (ω ₃ ) −D of the second term on the right side of equation (6)
(Ω ₂ ) can be obtained by the phase meter 104 as described above. D (ω ₁ ) of the first term on the right side is
It can be obtained by the phase meter 105. Therefore, in the arithmetic unit 108, the output signal 106 of the phase meter 104
Based on the output signal 107 of the phase meter 105 and the arithmetic expression of Expression (6), the true displacement D of the movable mirror can be obtained. In the light wave interference measuring apparatus of FIG.
Frequency omega ₂ of the light and the frequency omega ₃ of light from 0 passes through a predetermined optical path to the light and coaxial length measuring emitted from the light source 1. For this reason, even when the refractive index fluctuation of the air is not uniform along the measurement optical path and the reference optical path, the length measurement error caused by the air refractive index fluctuation is corrected, and the displacement amount of the movable mirror in the optical axis direction can be accurately determined. Can be measured.

However, in the optical interference measuring apparatus shown in FIG. 10, the optical path of the length measuring interferometer in which the refractive index fluctuation of the air is to be measured, the optical path of which the refractive index fluctuation is actually measured is from the polarization separation element 4. Only the optical path of the reference light and the optical path of the measurement light up to the frequency separation element 500 are provided. Therefore, the optical path from the frequency separation element 500 to the polarization coupling element 502 through which the light of frequency ω ₁ ′ as the reference light passes and the optical path from the frequency separation element 500 to the polarization coupling element 502 through which the light of frequency ω _{1 as} the measurement light passes In the above, the refractive index fluctuation is not measured even though the refractive index fluctuation needs to be measured. Further, an optical path and the measuring beam from the frequency separation element 500 is a reference light frequency omega ₂ of the light and the frequency omega ₃ light passes up to the frequency converter 509 frequency omega ₂
Frequency separating device 500 through which the light and the frequency omega ₃ light
In the optical path from to the frequency conversion element 517, not the optical path of the length measuring interferometer but the refractive index fluctuation is measured although the measurement of the refractive index fluctuation is unnecessary.

As described above, in the optical interference measurement apparatus shown in FIG. 10, the refractive index fluctuation is measured in the non-length measuring optical path where the measurement of the refractive index fluctuation is unnecessary, and the refractive index fluctuation is measured in the length measuring optical path which requires the measurement of the refractive index fluctuation. Rate fluctuations have not been measured. As a result, it is conceivable that the measurement accuracy of the device is reduced due to unnecessary measurement of refractive index fluctuation and lack of necessary measurement. The present invention has been made in view of the above-described problem, and suppresses a decrease in measurement accuracy due to unnecessary measurement of refractive index fluctuation and a lack of necessary measurement, and measures the length due to refractive index fluctuation in an optical path. It is an object of the present invention to provide a light wave interference measurement device capable of correcting an error with high accuracy.

[0030]

In order to solve the above-mentioned problems, according to the present invention, a light source for outputting a first light having a predetermined frequency, a second light and a third light having different frequencies from each other are provided. And a light source unit for outputting the first light from the light source along the same optical path, and the first light from the light source, the second light and the third light from the light source unit are coupled along the same optical path. And a reference light guided along a reference optical path to a fixed mirror through the first light, the second light, and the third light via the frequency coupling means. Polarization splitting means for splitting polarization into measurement light guided along a measurement optical path to a mirror, and a frequency of one of the second light and the third light via the measurement optical path. The first interference light is generated by substantially matching the frequency of the other light. A first interference light generating system, and a second interference light generated by making the frequency of one of the second light and the third light through the reference optical path substantially equal to the frequency of the other light. A second interference light generation system for generating
The first light, the second light, and the third light passing through the measurement light path and the first interference light generation system are referred to as the first light, the second light, and the third light. A first frequency separation unit for separating the first light, the second light, and the third light via the reference light path and the second interference light generation system into the first light; Light and the second
And second light for frequency separation into the third light and the third light.
Frequency separating means, and the first light separated by the first frequency separating means via the measurement light path and the first light separated by the second frequency separating means via the reference light path. A third interference light generation system for generating a third interference light based on the first interference light and the second interference light, the displacement amount of the movable mirror measured based on the third interference light. A light wave interference measurement device is provided which performs correction based on refractive index fluctuation information in the measurement optical path and the reference optical path measured based on light.

According to a preferred aspect of the present invention, the fixed mirror and the movable mirror emit the measurement light emitted from the polarization splitting means via the measurement optical path and the measurement light emitted from the polarization splitting means via the reference optical path. And the reference light to be spatially separated from each other. In this case, the fixed mirror and the movable mirror are each formed of a corner cube prism, and the position at which the reference light reflected by the fixed mirror is incident on the polarization splitting means, and the measurement light reflected by the movable mirror. It is preferable that the two corner cube prisms are arranged so that the position at which the light enters the polarization splitting means is substantially different.

Further, according to a preferred aspect of the present invention, the first interference light generation system includes the second interference light generation system via the measurement optical path.
First polarization rotating means for adjusting the polarization direction of at least one of the light and the third light, and the second light and the third light passing through the first polarization rotating means. A first frequency converter for making the frequency of one of the lights substantially equal to the frequency of the other light, and the second light and the third light via the first polarization rotating means for the first light.
A first condensing unit for condensing the light on a frequency conversion unit, wherein the second interference light generation system is configured to perform at least one of the second light and the third light via the reference light path. Second polarization rotating means for adjusting the polarization direction of the light,
Second frequency conversion means for making the frequency of one of the second light and the third light through the second polarization rotation means substantially equal to the frequency of the other light, and the second polarization And a second light condensing means for condensing the second light and the third light via the rotation means on the second frequency conversion means.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a first light for measuring a length via a measurement optical path and a reference optical path is used as a first interference light generation system and a second interference light generation system for measuring a change in refractive index. After passing through the system, is separated from the second light and the third light,
Interference occurs through the interference light generation system. With this configuration, in the present invention, the length measurement optical path where the measurement of the refractive index variation is not performed despite the need for the measurement of the refractive index variation is relatively short,
Even though the measurement of the refractive index fluctuation is unnecessary, there is no non-length measuring optical path in which the measurement of the refractive index fluctuation is performed. As a result, it is possible to avoid a decrease in measurement accuracy due to unnecessary measurement of refractive index fluctuation, and to suppress a decrease in measurement accuracy due to lack of measurement requiring refractive index fluctuation.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing a configuration of an optical interference measuring apparatus according to a first embodiment of the present invention. Also,
FIG. 2 is a diagram showing an internal configuration of the light source unit 50 of FIG.
In the light wave interference measuring apparatus of the first embodiment, the refractive index fluctuation is measured using a so-called homodyne interference method. The light wave interference measurement apparatus of FIG. 1 includes a light source unit 50 that supplies light for measuring a change in refractive index. Light source 5
0 emits a light of a frequency omega ₂ of the light and the frequency omega ₃ coaxially. The polarization direction of the light of frequency ω ₂ emitted from the light source unit 50 and the polarization direction of the light of frequency ω ₃ match each other, and are 45 ° with respect to the polarization direction of the light emitted from the length measuring light source 1 described later. At an angle.

Referring to FIG. 2, a light source unit 50 includes a light source 200 for emitting light of frequency ω ₂ and a frequency conversion element 20.
1 and a polarization rotation device 209. The light having the frequency ω ₂ emitted from the light source 200 enters the frequency conversion element 201. In the frequency converting element 201, a portion of the frequency omega ₂ of the light from the light source 200 becomes a frequency omega ₃ of the light is frequency converted and the remainder is transmitted remains frequency omega _2. The polarization direction of the light of frequency ω ₂ and the polarization direction of the light of frequency ω ₃ emitted from the frequency conversion element 201 are respectively adjusted by the operation of the polarization rotation device 209. As a result, the polarization direction of the light of frequency ω ₂ from the light source unit 50 matches the polarization direction of the light of frequency ω ₃ , and forms an angle of 45 ° with the polarization direction of the light emitted from the light source 1.

The light having the frequency ω _{2 and} the light having the frequency ω ₃ emitted from the light source unit 50 are reflected by the frequency coupling element 3 composed of, for example, a dichroic mirror, and are emitted from the length measuring light source 1 (in the vicinity of the frequency ω ₁ ). Light) and coaxially. The frequency coupling element 3 has a characteristic that transmits only light of the frequency omega ₁ near and reflects light of other frequencies. Light of the light and the frequency omega ₃ of the reflected frequency omega ₂ in frequency coupling element 3 is incident on the polarization separating element 4 such as a polarizing beam splitter. The polarization separation element 4 has a frequency ω
45 ° to the polarization direction of the light of frequency _{2 and} the light of frequency ω ₃
It is arranged only inclined. Therefore, the light incident on the polarization splitting element 4 is two lights, that is, the polarization splitting element 4
Are split into a reference light which is reflected by and guided to the fixed mirror 5 and a measurement light which is transmitted through the polarization separation element 4 and guided to the movable mirror 6. As described above, the polarization directions of the reference light and the measurement light are orthogonal to each other, and both the light of the frequency ω ₂ and the frequency ω
It includes both ₃ light.

The reference light reflected by the polarization beam splitter 4 is reflected by a fixed mirror 5 formed of, for example, a corner cube, and then returns to the polarization beam splitter 4 again. On the other hand, the polarization separation element 4
Is reflected by the movable mirror 6 formed of, for example, a corner cube, and then returns to the polarization separation element 4 again.
At this time, the reference light corner cube 5 and the measurement light corner cube 6 are arranged such that the incident point of the reference light and the incident point of the measurement light that re-enter the polarization separation element 4 do not substantially overlap each other. Have been.

Thus, the reference optical path (the optical path through which the reference light passes)
The light of the frequency ω _{2 and} the light of the frequency ω ₃ via the optical path are different from the light of the frequency ω _{2 and} the light of the frequency ω ₃ via the measuring optical path (the optical path through which the measuring light passes) (they are spatially separated from each other). Out of the polarization separation element 4 along the optical path. The reference light composed of the light having the frequency ω _{2 and} the light having the frequency ω ₃ emitted from the polarization separation element 4 enters the polarization rotation device 7. Further, the measurement light composed of the light having the frequency ω _{2 and} the light having the frequency ω ₃ emitted from the polarization separation element 4 enters the polarization rotation device 15 via the reflection mirrors 13 and 14. The reference light and the measurement light having passed through the polarization rotators 7 and 15 are condensed by the refractive optical elements 8 and 16, and then enter the frequency conversion elements 9 and 17, respectively.

[0039] In the frequency converter 9 and 17, the light of the frequency omega ₂ lower frequency is a harmonic converted to a higher frequency omega ₃ optical frequencies, optical frequencies omega ₃ high frequency is transmitted as it is. The light having the frequency ω ₃ whose frequency has been converted by the frequency conversion elements 9 and 17 is emitted from the light source unit 50 and interferes with the light having the frequency ω ₃ via a predetermined optical path. The interference light generated via the frequency conversion elements 9 and 17 is
After being converted into parallel light by the refractive optical elements 10 and 18, the light enters the frequency separation elements 11 and 19, respectively. Frequency separating device 11 and 19, for example, a dichroic mirror, having a characteristic that reflects only light of the frequency omega ₁ near and transmits light of other frequencies. Therefore, by the action of the frequency separation elements 11 and 19,
The light of frequency ω _{2 and} the light of frequency ω ₃ are
It is separated from the light (the frequency omega ₁ near the light) from.

The interference light transmitted through the frequency separation element 11 (the interference light between the light of frequency ω _{2 and} the light of frequency ω ₃ via the reference optical path) and the interference light transmitted through the frequency separation element 19 (via the measurement optical path) interference light) with a frequency omega ₂ of the light and the frequency omega ₃ of light are converted, respectively photoelectric receiving element 51 and 52. Thus, the light receiving element 51, the interference signal 102 based on the light of the light and the frequency omega ₃ frequency omega ₂ via a reference light path is produced. Further, the light receiving element 52, the interference signal 103 based on the light of the frequency omega ₂ of the light and the frequency omega ₃ through the measurement optical path is produced. Interference signal 102 from light receiving element 51 and interference signal 10 from light receiving element 52
3 are both supplied to the phase meter 104.

In the phase meter 104, the interference signal 102 based on the light of the frequency ω _{2 and} the light of the frequency ω ₃ via the reference optical path via the reference optical path, and the light of the frequency ω ₂ via the measurement optical path and the frequency ω ₃ based on the phase difference between the interfering signal 103 that is based on an optical, optical path length variation with respect to the frequency omega ₃ light D (omega
{D (ω ₃ ) −D (ω ₂ )}, which is the difference between ₃ ) and the optical path length change D (ω ₂ ) for the light of frequency ω ₂ . The signal 106 related to {D (ω ₃ ) −D (ω ₂ )} obtained by the phase meter 104 is supplied to the arithmetic unit 108.

The optical interference measuring apparatus shown in FIG.
A light source 1 for measuring the length of the displacement in the optical axis direction (the direction of the arrow in the figure) is provided. Light source 1 for length measurement
Is light and the frequency omega ₁ of the frequency _{ω 1 '(ω 1' =} ω 1 + Δ
ω ₁ ). The two lights emitted from the length measuring light source 1 have slightly different frequencies from each other,
The polarization directions are orthogonal to each other. The lights of two different frequencies emitted from the length measuring light source 1 enter the polarization separation element 4 via the light separation element 2 and are separated into light of the frequency ω ₁ ′ and light of the frequency ω _1. . The light having the frequency ω ₁ ′ becomes reference light, is reflected by the fixed mirror 5, and returns to the polarization splitting element 4 again. Further, the light of frequency ω ₁ becomes the measuring light, and the movable mirror 6
, And returns to the polarization separation element 4 again. As described above, the incident point of the reference light and the incident point of the measurement light that re-enter the polarization splitting element 4 are configured not to substantially coincide with each other.

[0043] Thus, the light and the measurement light path through the polarization separating element frequency omega ₁ emitted from 4 light through a reference light path frequency omega ₁ emitted from the polarization separating element 4 ', the different optical paths from each other Along the polarization rotators 7 and 15 and the refractive optical elements 8 and 16
And 17 respectively. Reference light and measurement light frequency omega ₁ of the frequency omega ₁ 'via the frequency converter 9 and 17 are converted into parallel light by the refractive optical element 10 and 18, respectively incident on the frequency separating device 11 and 19 . Thus, the reference light frequency omega ₁ 'along the same optical path as the reference beam composed of the frequency omega ₂ of the light and the frequency omega ₃ light, the frequency omega ₁ of the measuring light frequency omega ₂ of the light and the frequency omega ₃ Along the same optical path as the measurement light consisting of
It reaches the frequency separation elements 11 and 19, respectively.

As described above, the frequency separation elements 11 and 19 have a characteristic of reflecting only light near the frequency ω ₁ and transmitting light of other frequencies. Therefore, by the operation of the frequency separation elements 11 and 19, the reference light having the frequency ω ₁ ′ and the measurement light having the frequency ω ₁ are separated from the light having the frequency ω _{2 and} the light having the frequency ω ₃ from the light source unit 50. That is, the reference light of the frequency ω ₁ ′ reflected by the frequency separation element 11 is directly reflected, and the measurement light of the frequency ω ₁ reflected by the frequency separation element 19 is reflected by the reflecting mirror 20. The light is incident on such a polarization coupling element 12, respectively.

The reference light and the frequency omega ₁ of the measuring light is coupled coaxially through the polarization coupling element 12 the frequency omega ₁ 'interferes through the polarizer 21. The interference light generated via the polarizing plate 21 is photoelectrically converted by the light receiving element 22. The light receiving element 22 receives a measurement beat signal (frequency Δ
ω ₁ ) 101 is supplied to a phase meter 105. On the other hand, a part of the light of two different frequencies emitted from the length measuring light source 1 is reflected by the light separating element 2 and interferes via the polarizing plate 23. The interference light generated through the polarizing plate 23 is photoelectrically converted by the light receiving element 24, and the reference beat signal (frequency Δ
ω ₁ ) 100 is input to the phase meter 105.

In the phase meter 105, the reference beat signal 100
, The displacement D (ω ₁ ) of the movable mirror 6 without considering the influence of the refractive index fluctuation is obtained, and a signal 107 relating to the displacement D (ω ₁ ) is obtained. It is supplied to the arithmetic unit 108. Arithmetic unit 1
In step 08, the displacement D (ω ₁ ) of the movable mirror 6 measured by the length measuring interferometer using the light source 1 is corrected, and the true displacement (geometric distance) D of the movable mirror is obtained. That is, the arithmetic unit 108 outputs the output signal 106 of the phase meter 104 and the phase meter 10
5 based on the output signal 107 of Expression 5 and the operation expression of Expression (6),
The true displacement amount D of the movable mirror 6 in which the measurement error caused by the refractive index fluctuation is corrected is output.

As described above, in the first embodiment, in the frequency separation elements 11 and 19 disposed behind the frequency conversion elements 9 and 17, the light of the frequency ω ₁ for measuring the displacement of the movable mirror and the light of the frequency ω ₁ are measured. The light of frequency ω ₁ ′ is separated from the light of frequency ω _{2 and} the light of frequency ω ₃ for measuring the refractive index fluctuation. As a result, from the frequency separation element 9 through which the light of the frequency ω ₁ ′ as the reference light passes, the polarization coupling element 1
A relatively short optical path up to 2 and a frequency ω ₁ which is the measuring light
In a relatively short optical path from the frequency separation element 17 to the polarization coupling element 12 through which the light passes, the refractive index fluctuation is not measured even though the refractive index fluctuation needs to be measured. However, in the first embodiment, not the optical path of the length measuring interferometer but the optical path in which the refractive index fluctuation is measured even though the measurement of the refractive index fluctuation is unnecessary does not exist at all.

As described above, in the first embodiment, although the measurement of the refractive index fluctuation is required, the length measuring optical path where the measurement of the refractive index fluctuation is not performed is relatively short, and the measurement of the refractive index fluctuation is unnecessary. Nevertheless, there is no non-length measuring optical path in which the measurement of the refractive index fluctuation is performed. Therefore, it is possible to avoid a decrease in measurement accuracy due to unnecessary measurement of the refractive index fluctuation. In addition, it is possible to suppress a decrease in measurement accuracy due to a lack of required measurement of refractive index fluctuation. As a result, in the first embodiment, a length measurement error caused by a change in the refractive index of the optical path can be corrected with high accuracy.

The optical interference measuring apparatus of the first embodiment can measure the magnitude of the refractive index fluctuation on the optical path, but cannot determine the direction of the refractive index fluctuation, that is, the sign. That is, ΔD (ω ₃ ) −D in equation (6)
Although the absolute value of (ω ₂ )｝ can be obtained, D
It is impossible to determine whether D (ω ₂ ) is small or large with respect to (ω ₃ ). Therefore, in order to determine the direction of the refractive index fluctuation, the light receiving elements 51 and 5 shown in FIG.
For each of the interference signals 102 and 103 respectively detected in step 2, it is necessary to obtain signals that are out of phase by 90 °.

A method of obtaining a signal whose phase is shifted by 90 ° is generally well known. For example, the light receiving element 51
Is divided into two interference light beams, and the phase of one of the two divided interference light beams is shifted by 90 ° with respect to the phase of the other interference light beam. The direction of the refractive index fluctuation can be determined from the two signals obtained by the two interference lights. In order to shift the phase of one interference light by 90 ° with respect to the phase of the other interference light, a wave plate, a polarizing element, or the like can be used. Similarly, the direction of the refractive index fluctuation can be determined for the interference light detected by the light receiving element 52.

FIG. 3 is a diagram showing a first modification of the light source unit 50 of FIG. The light source unit 50 shown in FIG. 3 emits light having two different frequencies, that is, light having a frequency ω ₂ and light having a frequency ω ₃ along optical paths substantially parallel to each other.
It has. The light of frequency ω ₂ emitted from the light source 210 passes through the reflecting mirror 207, and the light of frequency ω ₃ is
The light enters the frequency coupling elements 208 respectively. Frequency separating device 208 has for example, a dichroic mirror, a characteristic of reflecting light of a frequency omega _2, transmits light of a frequency omega _3. Therefore, the frequency coupling element 208
The light of the frequency ω _{2 and} the light of the frequency ω ₃ which are coupled through the light are emitted coaxially from the light source unit 50 via the polarization rotation device 209. It is also possible to constitute the reversed optical path of the optical path and the frequency omega ₃ optical frequency omega ₂ of the light in the above description. Further, without being limited to the configuration of FIG.
Various modifications of 0 are possible.

FIG. 4 is a diagram showing a second modification of the light source unit 50 of FIG. By employing the light source unit 50 of the second modified example with respect to the configuration of the light wave interference measuring device of FIG. 1, it is possible to measure the refractive index fluctuation using a so-called heterodyne interference method. In the light source unit 50 of FIG. 4, in order to detect interference light between the light of the frequency ω _{2 and} the light of the frequency ω ₃ using the heterodyne method, the light source unit 50 is disposed in an optical path between the frequency conversion element 201 and the polarization rotation device 209. , Frequency separation element 205,
A frequency modulation element 202, a frequency coupling element 208, and reflection mirrors 206 and 207 are additionally provided.

Therefore, the light of frequency ω _{2 and} the light of frequency ω ₃ emitted from the frequency conversion element 201 enter the frequency separation element 205. Frequency separation element 205
Includes for example, a dichroic mirror, a characteristic of reflecting light of a frequency omega _2, transmits light of a frequency omega _3. Frequency ω ₂ reflected by frequency separation element 205
Are reflected by the reflecting mirrors 206 and 207 and then enter the frequency coupling element 208. On the other hand, light of frequency omega ₃ transmitted through the frequency separating device 205 is, for example, frequency-modulated via a frequency modulator element 202 consisting of acousto-optic device, the frequency omega ₃ which slightly shifted in frequency from the frequency omega ₃ '
(Ω ₃ ′ = ω ₃ + Δω ₃ ), and the frequency coupling element 2
08. Note that the frequency coupling element 208 has the same function as the frequency separation element 205. Thus, the light of frequency ω _{2 and} the light of frequency ω ₃ ′ coupled via the frequency coupling element 208 are emitted coaxially from the light source unit 50 via the polarization rotation device 209.

Frequency ω coaxially emitted from light source unit 50
The light of frequency _{2 and} the light of frequency ω ₃ ′ enter the frequency conversion elements 9 and 17 via the same optical paths as the light of frequency ω _{2 and} the light of frequency ω ₃ in the first embodiment of FIG. Specifically, the light of the frequency ω _{2 and} the light of the frequency ω ₃ ′ via the reference optical path are supplied to the frequency conversion element 9, and the light of the frequency ω _{2 and} the light of the frequency ω ₃ ′ via the measurement optical path are supplied to the frequency conversion element 9. 1
7 is incident. In the frequency conversion element 9, the frequency ω of the light of the frequency ω _{2 and} the light of the frequency ω ₃ ′ via the reference optical path
The light of ₂ is frequency-converted into light of frequency ω ₃ and the frequency ω ₃ ′
Is transmitted through the frequency conversion element 9 as it is.

As described above, when the light source unit 50 according to the second modified example shown in FIG. 4 is used for the configuration of the optical interference measuring apparatus shown in FIG. 1, two lights whose frequencies are different from each other by Δω _3, that is, the frequency ω ₃ The light and the light having the frequency ω ₃ ′ undergo heterodyne interference via the frequency conversion element 9. Similarly, the light of the frequency ω _{2 and} the light of the frequency ω ₃ ′ via the measurement optical path also undergo heterodyne interference via the frequency conversion element 17. Therefore, the interference signal 102 from the light receiving element 51
And the interference signal 103 from the light receiving element 52 becomes an interference beat signal. In the phase meter 104, based on the interference beat signal 102 and the interference beat signal 103, ΔD (ω
₃ ′) − D (ω ₂ )}. The signal 106 regarding {D (ω ₃ ′) −D (ω ₂ )} obtained by the phase meter 104 is
It is supplied to the arithmetic unit 108. Therefore, the arithmetic unit 108
Then, based on the output signal 106 of the phase meter 104 and the output signal 107 of the phase meter 105, the true displacement amount D of the movable mirror can be obtained by the arithmetic expression of Expression (6).

Further, in the second modified example, the refractive index fluctuation measurement using the light having the frequency ω _{2 and} the light having the frequency ω ₃ is performed by the heterodyne interference method. For this reason, it is difficult to receive an error due to the output fluctuation of the light source unit 50, and the phase difference ΔD (ω ₃ ′)
−D (ω ₂ )} can be accurately detected. As a result, in the lightwave interference measurement device using the light source unit 50 according to the second modification, the accuracy of detecting the true displacement D of the movable mirror can be improved.

FIG. 5 is a diagram showing a third modification of the light source unit 50 of FIG. The third modification has a configuration similar to that of the second modification of FIG. Therefore, by employing the light source unit 50 of the third modified example with respect to the configuration of the optical interference measurement apparatus of FIG. 1, it is possible to measure the refractive index fluctuation using the heterodyne interference method. However, while provided with a frequency modulation device 202 for frequency modulation only light of the frequency omega ₃ in the second variation, respectively, at the frequency of light of the frequency omega ₂ of the light and the frequency omega ₃ in the third modification Frequency modulation elements 204 and 203 for performing modulation are provided.

In the third modification shown in FIG. 5, the light of frequency ω ₂ reflected by the frequency separation element 205
After the light is reflected by the mirror 207, the light becomes the light of the frequency ω ₂ ′ (ω ₂ ′ = ω ₂ + Δω ₂ ) via the frequency modulation element 204,
And enters the frequency coupling element 208 via. On the other hand, the light of the frequency ω ₃ transmitted through the frequency separation element 205 becomes the light of the frequency ω ₃ ′ via the frequency modulation element 203 and enters the frequency coupling element 208. Thus, the light having the frequency ω ₂ ′ and the light having the frequency ω ₃ ′ coupled via the frequency coupling element 208 are emitted coaxially from the light source unit 50 via the polarization rotation device 209. Thus, in the third modification, since the frequency modulation of both the frequency omega ₂ of the light and the frequency omega ₃ light, it is possible to reduce a measurement error due to return light to the light source.

FIG. 6 is a diagram schematically showing the configuration of an optical interference measuring apparatus according to a second embodiment of the present invention. The second embodiment has a configuration similar to that of the first embodiment of FIG. 1 except that the measurement optical path is configured as a so-called double path.
Basically different from the embodiment. Therefore, in FIG. 6, elements having the same functions as those of the first embodiment are denoted by the same reference numerals as in FIG. Hereinafter, the second embodiment will be described by focusing on the differences from the first embodiment.

In the second embodiment shown in FIG. 6, a plane mirror 305 is used as a movable mirror. For a double-pass configuration of the measurement optical path, a reflecting mirror 306 made of, for example, a corner cube and a quarter-wave plate 304 are additionally provided.
Therefore, the measurement light transmitted through the polarization separation element 4 is 1 /
After being reflected by the moving mirror 305 via the four-wavelength plate 304,
The light returns to the polarization separation element 4 via the quarter-wave plate 304. 1
By passing through the quarter-wave plate 304 twice, the polarization direction of the measurement light returned to the polarization separation element 4 is rotated by 90 °. Therefore, the measurement light returned to the polarization separation element 4 is reflected by the polarization separation element 4 and enters the corner cube 306. The measurement light reflected by the corner cube 306 is reflected again by the polarization beam splitter 4, and the 光 wavelength plate 30
The light is reflected again by the moving mirror 305 via the light source 4. Moving mirror 30
The measurement light reflected again at 5 returns to the polarization splitting element 4 via the 波長 wavelength plate 304.

As described above, the second embodiment employs a double-pass configuration in which the measurement light reciprocates twice in the optical path to the movable mirror 305, so that measurement can be performed with higher resolution.
Other configurations and operations are the same as those of the first embodiment, and therefore, duplicated description will be omitted. Also, the second
In a case where the refractive index fluctuation is measured by the heterodyne interference method in the embodiment, the light source unit 50 in FIG. 6 may be configured according to the second modification or the third modification.

FIG. 7 is a diagram schematically showing the configuration of an optical interference measuring apparatus according to a third embodiment of the present invention. The third embodiment has a configuration similar to that of the second embodiment of FIG. 6, but is basically different from the second embodiment only in that not only the measurement optical path but also the reference optical path is configured as a double path. Therefore, in FIG. 7, elements having the same functions as those of the second embodiment are denoted by the same reference numerals as in FIG. Hereinafter, the third embodiment will be described by focusing on the differences from the second embodiment.

In the third embodiment shown in FIG. 7, a plane mirror 302 is used as a fixed mirror. For a double-pass configuration of the reference optical path, a polarization splitting element 300 composed of, for example, a polarization beam splitter, a reflecting mirror 303 composed of, for example, a corner cube, and a quarter-wave plate 301 are additionally provided. Therefore, the reference light reflected by the polarization separation element 4 is combined with the polarization separation element 300 and the 波長 wavelength plate 301.
, And enters the fixed mirror 302. The reference light reflected by the fixed mirror 302 returns to the polarization separation element 300 via the quarter-wave plate 301. By passing through the quarter-wave plate 301 twice, the polarization direction of the reference light returned to the polarization separation element 300 is rotated by 90 °. Therefore, the reference light returned to the polarization beam splitter 300 passes through the polarization beam splitter 300 and enters the corner cube 303.

The reference light reflected by the corner cube 303 passes through the polarization splitter 300 again, and is reflected again by the fixed mirror 302 via the quarter-wave plate 301. The reference light reflected again by the fixed mirror 302 is a quarter-wave plate 301
And returns to the polarization separation element 300. 1/4 wavelength plate 30
1 two more times, the polarization splitting element 30
The polarization azimuth of the reference light that has returned to 0 is further rotated by 90 ° and returned to the original position. Therefore, the reference light returned to the polarization beam splitter 300 is reflected by the polarization beam splitter 300 and returns to the polarization beam splitter 4.

As described above, the third embodiment employs a double-pass configuration in which the measurement light and the reference light reciprocate twice in the optical path to the movable mirror 305 and the fixed mirror 302, respectively. The surface and the reflecting surface of the plane mirror forming the fixed mirror 302 are configured to be parallel to each other. Therefore, by using the optical interference measuring apparatus of the third embodiment, even when the relative displacement between the fixed mirror and the movable mirror is measured in an exposure apparatus for manufacturing a semiconductor element or a liquid crystal display element, for example, High-resolution measurement becomes possible. The other configurations and operations are the same as those of the second embodiment, and therefore, the duplicate description will be omitted. In the case where the refractive index fluctuation is measured by the heterodyne interference method in the third embodiment, the light source unit 50 in FIG. 7 may be configured according to the second modification or the third modification.

FIG. 8 is a diagram schematically showing the configuration of an optical interference measuring apparatus according to a fourth embodiment of the present invention. The fourth embodiment has a configuration similar to that of the first embodiment shown in FIG. 1, except that the arrangement of the frequency separation elements 11 and 19 and the refractive optical systems 10 and 18 is reversed. Different.
Therefore, in FIG. 8, elements having the same functions as those of the first embodiment are denoted by the same reference numerals as those in FIG. Hereinafter, the fourth embodiment will be described focusing on the differences from the first embodiment.

In the fourth embodiment shown in FIG.
The frequency separation elements 11 and 19 are arranged between the optical system 10 and the refractive optical system 10 and the refraction optical system 10 and 18, respectively. Therefore, a refractive optical system 610 is provided between the frequency separating element 11 and the polarization coupling element 12, and a refractive optical system 618 is provided between the frequency separating element 19 and the polarization coupling element 12. With the configuration described above, also in the fourth embodiment, similarly to the first embodiment, it is possible to relatively shorten the length measuring optical path in which the measurement of the refractive index fluctuation is required but the measurement of the refractive index fluctuation is not performed. it can. As a result, a length measurement error caused by a change in the refractive index of the optical path can be corrected with high accuracy.

FIG. 9 is a diagram schematically showing a configuration of an optical interference measuring apparatus according to a fifth embodiment of the present invention. The fifth embodiment has a configuration similar to that of the first embodiment of FIG. 1, but is basically different from the first embodiment only in that an enclosing member 90 indicated by a broken line in FIG. 9 is provided. Therefore, in FIG.
Elements having the same functions as those of the embodiment are denoted by the same reference numerals as in FIG. The fifth embodiment will be described below, focusing on the differences from the first embodiment.

In the fifth embodiment shown in FIG. 9, the enclosing member 90 surrounds the length measuring optical path in which the measurement of the refractive index fluctuation is required but the refractive index fluctuation is not measured. Specifically, the optical path from the frequency separation element 9 through which the light of the frequency ω ₁ ′ as the reference light passes to the polarization coupling element 12 and the frequency separation element 17 through which the light of the frequency ω _{1 as} the measurement light passes through the polarization coupling element 12 The optical path up to is enclosed by the enclosing member 90.

Therefore, in the fifth embodiment, the fluctuation of the refractive index of the length measuring optical path in which the measurement of the refractive index fluctuation is not performed even though the measurement of the refractive index fluctuation is necessary is suppressed by the action of the surrounding member 90. it can. Also, the surrounding member 90
By substituting the inside with another gas or making it almost in a vacuum state, it is necessary to configure so that there is no length measuring optical path where the refractive index fluctuation is not measured even though the refractive index fluctuation is required to be measured. Is also possible. As a result, also in the fifth embodiment, it is possible to correct the length measurement error caused by the change in the refractive index of the optical path with high accuracy.

In each of the above embodiments, the light emitted from the polarization splitter via the measurement optical path and the light emitted from the polarization splitter via the reference optical path are spatially separated. A movable mirror and a fixed mirror are appropriately arranged. However, for example, a deflecting unit is arranged between the polarization splitting element and the movable mirror so that the light passing through the measurement optical path is spatially separated from the light passing through the reference optical path without passing through the polarization splitting element. You can also.

[0072]

As described above, according to the present invention, unnecessary measurement of refractive index fluctuation and reduction in measurement accuracy due to lack of necessary measurement are suppressed, and length measurement error due to refractive index fluctuation in the optical path is suppressed. Can be realized with high accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an optical interference measuring apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an internal configuration of a light source unit 50 of FIG.

FIG. 3 is a diagram showing a first modification of the light source unit 50 of FIG.

FIG. 4 is a diagram showing a second modification of the light source unit 50 of FIG.

FIG. 5 is a diagram showing a third modification of the light source unit 50 of FIG.

FIG. 6 is a diagram schematically showing a configuration of an optical interference measuring apparatus according to a second embodiment of the present invention.

FIG. 7 is a diagram schematically showing a configuration of an optical interference measurement apparatus according to a third embodiment of the present invention.

FIG. 8 is a diagram schematically showing a configuration of an optical interference measurement apparatus according to a fourth embodiment of the present invention.

FIG. 9 is a diagram schematically showing a configuration of an optical interference measuring apparatus according to a fifth embodiment of the present invention.

FIG. 10: Japanese Patent Application No. 7-60969 and Japanese Patent Application No. 7-6
It is a figure which shows roughly the structure of the lightwave interference measuring apparatus disclosed by the specification and drawing of No. 4537.

FIG. 11 is a diagram schematically showing a configuration of a conventional light wave interference measurement device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1, 200, 210 Light source 50 Light source part 2 Light separation element 3, 208 Frequency coupling element 4, 300, 400 Polarization separation element 5, 302 Fixed mirror 6, 305 Moving mirror 7, 15, 209 Polarization rotation device 8, 10, 16 , 18, 610, 618 Refractive optical element 9, 17, 201 Frequency conversion element 11, 19, 205 Frequency separation element 12, 502 Polarization coupling element 13, 14, 20, 206, 207, 303, 306
Reflecting mirror 21, 23 Polarizing plate 22, 24, 51, 52 Light receiving element 104, 105 Phase meter 108 Operation unit 202-204 Frequency modulation element 301, 304 Quarter wave plate 532 Air sensor

Claims (9)

[Claims] A light source for outputting a first light having a predetermined frequency; a light source for outputting a second light and a third light having different frequencies along the same optical path; A frequency coupling unit for coupling the first light from the light source, the second light and the third light from the light source unit along the same optical path, and The first light, the second light, and the third light are respectively polarized into a reference light guided along a reference optical path to a fixed mirror and a measurement light guided along a measurement optical path to a movable mirror. Polarization splitting means for splitting, and generating a first interference light by making a frequency of one of the second light and the third light through the measurement optical path substantially equal to a frequency of the other light. A first interference light generation system for performing A second interference light generation system for generating a second interference light by making a frequency of one of the second light and the third light substantially equal to a frequency of the other light; and The first light, the second light, and the third light via the first interference light generation system are frequency-separated into the first light, the second light, and the third light. A first frequency separating unit, and the first light, the second light, and the third light via the reference light path and the second interference light generation system, and the first light and the second light. Second frequency separating means for frequency-separating the second light and the third light, and the first light and the reference light separated by the first frequency separating means via the measurement optical path. And third interference based on the first light separated by the second frequency separation means. And a displacement amount of the movable mirror measured based on the third interference light is measured based on the first interference light and the second interference light. A light-wave interference measuring apparatus, wherein the correction is performed based on the refractive index fluctuation information in the measurement optical path and the reference optical path. 2. The apparatus according to claim 1, wherein the fixed mirror and the movable mirror separate measurement light emitted from the polarization splitting unit through the measurement optical path and reference light emitted from the polarization splitting unit through the reference optical path. The light wave interference measurement device according to claim 1, wherein the light wave interference measurement device is arranged so as to be spatially separated. 3. The fixed mirror and the movable mirror each include a corner cube prism, and a position where the reference light reflected by the fixed mirror is incident on the polarization splitting means, and a position reflected by the movable mirror. 3. The optical interference measuring apparatus according to claim 2, wherein the two corner cube prisms are arranged so that a position where the measuring light is incident on the polarization splitting means is substantially different. 4. A first polarization rotating means for adjusting a polarization direction of at least one of the second light and the third light via the measurement optical path. And first frequency conversion means for making the frequency of one of the second light and the third light through the first polarization rotation means substantially equal to the frequency of the other light; and A first condensing unit for condensing the second light and the third light via the one polarization rotating unit on the first frequency conversion unit; and the second interference light generation system A second polarization rotation unit for adjusting a polarization direction of at least one of the second light and the third light via the reference optical path, and the second polarization rotation unit via the second polarization rotation unit. The frequency of one of the second light and the third light is approximately the same as the frequency of the other light. A second frequency converting means for making the two light beams coincide with each other, and a second light condensing means for condensing the second light and the third light via the second polarization rotating means on the second frequency converting means. The light wave interference measurement apparatus according to claim 1, further comprising: 5. The light source outputs light including light having a frequency ω ₁ and light having a frequency ω ₁ ′ whose frequencies are slightly different from each other and whose polarization directions are orthogonal to each other, as the first light, The polarization separation means separates the light of the frequency ω ₁ into the measurement light and the light of the frequency ω ₁ ′ into the reference light, respectively. Light wave interferometer. 6. The first light source for outputting the second light and the third light along different optical paths, respectively, and the second light from the first light source. The optical interference measurement apparatus according to claim 1, further comprising: a frequency coupling element for coupling the third light with the third light on the same optical path. 7. The light source unit includes: a second light source for outputting the second light; and a part of the second light from the second light source, which is converted into a harmonic. A third light for outputting as the third light
Frequency conversion means, wherein the first interference light generation system has fourth frequency conversion means for converting the second light through the measurement optical path into a harmonic, and the second interference light The light wave interference according to any one of claims 1 to 5, wherein the generation system includes a fifth frequency conversion unit configured to convert the second light having passed through the reference light path into a harmonic. measuring device. 8. The light source unit further includes frequency modulation means for slightly modulating the frequency of at least one of the second light and the third light. The optical interference measurement apparatus according to claim 6. 9. The apparatus according to claim 1, wherein at least one of said movable mirror and said fixed mirror is a plane mirror.
9. The light wave interference measurement apparatus according to any one of claims 8 to 8.