KR101678891B1 - Direction deterministic spectrally-resolved interferometry using a dispersive plate and measuring system using the same - Google Patents
Direction deterministic spectrally-resolved interferometry using a dispersive plate and measuring system using the same Download PDFInfo
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- KR101678891B1 KR101678891B1 KR1020150185907A KR20150185907A KR101678891B1 KR 101678891 B1 KR101678891 B1 KR 101678891B1 KR 1020150185907 A KR1020150185907 A KR 1020150185907A KR 20150185907 A KR20150185907 A KR 20150185907A KR 101678891 B1 KR101678891 B1 KR 101678891B1
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- 238000005305 interferometry Methods 0.000 title description 3
- 230000003287 optical effect Effects 0.000 claims abstract description 53
- 239000000463 material Substances 0.000 claims abstract description 11
- 239000006185 dispersion Substances 0.000 claims description 87
- 238000005259 measurement Methods 0.000 claims description 59
- 238000000034 method Methods 0.000 claims description 16
- 239000005350 fused silica glass Substances 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 5
- 239000011521 glass Substances 0.000 claims description 5
- 230000000694 effects Effects 0.000 abstract description 4
- 230000000149 penetrating effect Effects 0.000 abstract 2
- 238000010586 diagram Methods 0.000 description 6
- 230000002452 interceptive effect Effects 0.000 description 2
- 238000012886 linear function Methods 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 1
- 239000000284 extract Substances 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000004907 flux Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000013178 mathematical model Methods 0.000 description 1
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 1
- 229910052753 mercury Inorganic materials 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02041—Interferometers characterised by particular imaging or detection techniques
- G01B9/02044—Imaging in the frequency domain, e.g. by using a spectrometer
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02015—Interferometers characterised by the beam path configuration
- G01B9/02016—Interferometers characterised by the beam path configuration contacting two or more objects
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B9/00—Measuring instruments characterised by the use of optical techniques
- G01B9/02—Interferometers
- G01B9/02083—Interferometers characterised by particular signal processing and presentation
- G01B9/02085—Combining two or more images of different regions
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/0205—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows
- G01J3/0208—Optical elements not provided otherwise, e.g. optical manifolds, diffusers, windows using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/28—Investigating the spectrum
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/10—Beam splitting or combining systems
- G02B27/1006—Beam splitting or combining systems for splitting or combining different wavelengths
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/30—Collimators
Abstract
Description
The present invention relates to a directionally discriminating dispersion interferometer using a dispersion plate and a measurement system using the same, and more particularly, to a dispersion interferometer capable of discriminating the directionality of a distance by using a non- And a measurement system using the same.
The interferometer is an optical device using superposition of waves and has a very long history. Until the laser was created, a mercury lamp or natural light was passed through the filter to create a simulated monochromatic light to create an interference pattern. Since the laser is emitted, the interferometer is relatively simple in configuration, and coherence is good, so observation of the interference pattern is relatively easy. For example, if you look at the Michelson interferometer, you can configure one laser and two reflectors as a photodetector or one screen. In order to obtain a stopped interference pattern over time, the laser used as the light source must have a single frequency. To do this, we usually use gas lasers such as He-Ne lasers. Since solid or semiconductor lasers have a wide optical gain wavelength range, a separate technique such as external feedback can be used to obtain a single wavelength for transverse mode or longitudinal mode filtering.
Such an interferometer is widely used for practical and precise length measurement, and can be used particularly as a sensor for detecting a position when driving a precision stage. When the two optical path differences of the interferometer are at one wavelength, the final interference fringe also moves for one period. Usually, one optical path is fixed and the other one is attached to the moving stage to move the stage more finely To be measured.
A spectrally-resolved interferometry or a dispersive interferometry can obtain an interference signal according to a wavelength using a light source of a wide frequency band, and is widely used for distance or thickness measurement.
Such a dispersion interferometer can establish an appropriate mathematical model and convert an interfering signal according to wavelength into an interfering signal according to optical frequency. By analyzing the interference signal for each optical frequency, it is possible to measure the optical path difference between the reference light coming back and coming from the reference mirror and the measuring light coming back and returning to the measuring area, and the resolution of several nm The distance can be measured.
Distance measurement can be measured by various methods. As a method of extracting the phase value from the interference signal, a method of extracting peaks using synchronous sampling or Fourier transform is used as a typical method .
The conventional distance measurement method extracts a phase signal according to frequency in the analysis process of a dispersion interferometer, and measures the distance through the slope of the extracted phase signal.
However, the existing distance measurement method is characterized in that a distance value having a positive sign is always measured irrespective of the distance, such as the distance between the reference mirror and the measurement mirror, or the distance from the reference mirror. .
As a result of efforts to solve the problems and disadvantages of the related art as described above, the present inventors have completed the present invention by inserting a dispersion plate in a reference path or a measurement path in a dispersion interferometer structure to cause random dispersion.
SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a dispersion interferometer capable of discriminating the directionality of a distance using a nonlinear component of phase per optical frequency extracted from the dispersion interferometer.
It is still another object of the present invention to provide a measurement system using a dispersion interferometer capable of extending a measurement region through directional discrimination of a dispersion interferometer.
The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.
According to an aspect of the present invention, there is provided an optical system including a light splitter for partially reflecting and partially transmitting light from a light source; A reference mirror arranged at a position perpendicular to a path of the light, the reference mirror reflecting the light reflected from the light splitter; A measurement object mirror arranged on the path of the light and reflecting the light transmitted through the optical splitter; A dispersion plate arranged between the optical splitter and the reference mirror or between the optical splitter and the measurement target mirror and made of a material whose refractive index is changed according to a wavelength; And a light source unit arranged at a position perpendicular to a path of the light, the light reflected by the reference mirror and transmitted again by the optical splitter, and the light reflected by the measurement target mirror and reflected by the optical splitter, The present invention provides a directionally discriminating dispersion interferometer using a dispersion plate, characterized in that a phase of each measured optical frequency has a nonlinear component and a direction can be discriminated.
In a preferred embodiment, the reference mirror and the measurement object mirror are fixed and arranged.
In a preferred embodiment, the diffuser plate is made of glass or fused silica.
In a preferred embodiment, the light source further includes a collimator lens arranged between the light source and the light splitter, the collimator lens converting the light from the light source into parallel light.
In order to achieve the above object, the present invention also provides a dispersion interferometer comprising a dispersion plate arranged on a light path and made of a material whose refractive index varies with a wavelength; And a determiner for measuring a distance or a thickness using a signal detected from the dispersion interferometer, wherein a phase of each optical frequency measured from the dispersion interferometer has a nonlinear component, and the determiner uses the nonlinear component information And the distance or thickness is measured by discriminating the directionality.
In a preferred embodiment, the dispersion interferometer comprises: a light splitter for partially reflecting and partially transmitting light from a light source; A reference mirror arranged at a position perpendicular to a path of the light, the reference mirror reflecting the light reflected from the light splitter; A measurement object mirror arranged on the path of the light and reflecting the light transmitted through the optical splitter; A dispersion plate arranged between the optical splitter and the reference mirror or between the optical splitter and the measurement target mirror and made of a material whose refractive index is changed according to a wavelength; And a light source unit arranged at a position perpendicular to a path of the light, the light reflected by the reference mirror and transmitted again by the optical splitter, and the light reflected by the measurement target mirror and reflected by the optical splitter, And a spectroscope for detecting the light.
In a preferred embodiment, the reference mirror and the measurement object mirror are fixed and arranged.
In a preferred embodiment, the diffuser plate is made of glass or fused silica.
In a preferred embodiment, the dispersion interferometer further includes a collimator lens arranged between the light source and the light splitter, the collimator lens converting the light from the light source into parallel light.
In a preferred embodiment, the phase of each optical frequency measured from the dispersion interferometer has a nonlinearity represented by the following equation.
(Equation)
C 0 : Light speed during vacuum
L 1 : Distance between the beam splitter and the reference mirror
L 2 : Distance between the beam splitter and the target mirror
t: thickness of the dispersion plate
N d (υ): refractive index of diffuser plate
The present invention has the following excellent effects.
First, according to the directionally discriminating dispersion interferometer using the dispersion plate of the present invention, the directionality of the distance can be discriminated by using the nonlinear component of phase per optical frequency extracted from the dispersion interferometer, which has an advantage of increasing the measurement area.
In addition, according to the measurement system using the dispersion interferometer of the present invention, it is possible not only to extend the measurement region through directional discrimination of the dispersion interferometer, but also to eliminate unnecessary movement of the drive stage.
1 is a schematic block diagram of a directionally discriminating dispersion interferometer using a dispersion plate according to an embodiment of the present invention.
2 is a diagram illustrating a measurement process of a measurement system using a dispersion interferometer according to an embodiment of the present invention.
Fig. 3 is a diagram showing a measurement distance (a), a nonlinear coefficient (b), and a calibration distance (c) of a measurement system using a dispersion interferometer without a dispersion plate.
FIG. 4 is a diagram showing a measurement distance a, a nonlinear coefficient b, and a calibration distance c of a measurement system using a dispersion interferometer according to an embodiment of the present invention.
Although the terms used in the present invention have been selected as general terms that are widely used at present, there are some terms selected arbitrarily by the applicant in a specific case. In this case, the meaning described or used in the detailed description part of the invention The meaning must be grasped.
Hereinafter, the technical structure of the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.
However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals used to describe the present invention throughout the specification denote like elements.
1 is a schematic block diagram of a directionally discriminating dispersion interferometer using a dispersion plate according to an embodiment of the present invention.
1, a directional
First, the
The
The collimated light having passed through the
The
The
The
The parallel light reflected through the
The
At this time, the
The
When the parallel light that has passed through the
Since the nonlinearity of the phase varies with the direction in the dispersion interferometer, the directionality of the dispersion interferometer can be determined using the nonlinearity.
If the directionality of the dispersion interferometer can be determined as in the embodiment of the present invention, an effect of increasing the distance measurement area occurs.
Meanwhile, the direction-determining
2 is a diagram illustrating a measurement process of a measurement system using a dispersion interferometer according to an embodiment of the present invention.
The measurement system using the dispersion interferometer according to an embodiment of the present invention includes a
The
Referring to FIG. 2, the determination unit measures a distance or a thickness using a signal detected from the
The measurement principle of the measurement system using the applied dispersion interferometer is as follows.
Assuming that a distance from the
Where c 0 denotes the flux in vacuum and A (υ) and B (υ) denote the background intensity and envelope function of the dispersion interferometer and are determined by the spectral density of the light source do.
n 1 L 1 and n 2 L 2 represent the effective optical path lengths (OPL) of the reference mirror and the target mirror. At this time, in the case of a dispersion interferometer having no
The phase? (?) Can be expressed by Equation (2) expressed by the Fourier transform and the inverse Fourier transform, and the slope of the phase according to? Can be expressed by Equation (3).
It can be seen that the phase? (?) Is a sine function as shown in Equation (1). However, such a dispersion interferometer can measure only the value of L 2 -L 1 without distinguishing between (+) and (-) signals other than (L 2 -L 1 ). This means that the directionality can not be determined as shown in FIG. 3, that is, only the (+) value can always be measured.
A blank region having a value of L 2 -L 1 is a dead zone caused by L min .
Meanwhile, n 1 L 1 can be calculated by the thickness t and the refractive index n d of the
At this time, the phase? '(?) Can be expressed again by the following equation (5).
Then, the slope of the phase can be expressed by Equation (6).
Here, N d (v) represents the refractive index group of the diffusing plate, and can be expressed by the following equation (7).
At this time, it can be seen that the slope of the phase is not linear, as can be seen from Equation (6). That is, it can be seen that the insertion of the
As described above, the measurement system using the dispersion interferometer according to an embodiment of the present invention has a nonlinear component whose phase is represented by (L 2 -L 1 ), and measurement is possible from (+) to (-) values. Do.
The directionality of (L 2 -L 1 ) is determined by the nonlinear phase value in the above-mentioned equation (3).
In other words, N d (υ) can be estimated as a linear function of υ when the dispersion range of the light source is relatively narrow, and φ '(υ) can be expressed as a quadratic polynomial. At this time, the first coefficient of the polynomial is expressed by the amount of the nonlinear component, and is used to determine the directionality.
2, φ '(υ) is extracted from the interference signal detected by the
Here, the directional measurement is determined by the first coefficient, and the distance is calculated by the slope of the phase, which is the second coefficient. In this case, the calculated distance may cause an error by about t (1-n d ). This error can be calculated by applying the known thickness t of the diffusing plate and the refractive index n d . Do.
Example
LEDs with a wavelength of 880 nm (center wavelength) / 50 nm (bandwidth) were used as the light source, and the mirrors were mounted on the driving stage. A spectrometer having a measurement range width of 350 to 1000 nm and a resolution of about 0.8 nm was used. The theoretical Lmin and Lmax of 880nm LED are 15.4μm and 161.3μm, respectively. The dispersion plate used UV-fused silica having a thickness of 3.2 mm and arranged in the measuring path.
FIG. 3 is a view showing a measurement distance (a), a nonlinear coefficient (b), and a calibration distance (c) of a measurement system using a dispersion interferometer without a dispersion plate, (A), the nonlinear coefficient (b), and the calibration distance (c) of the measurement system using the interferometer.
FIG. 2 (b) shows the nonlinear coefficient of the phase and shows a linear function of the optical frequency.
That is, in the case of a measurement system using a dispersion interferometer without a dispersion plate, it can be seen that there is no nonlinear component, and it can be seen that the distance that can be measured is limited as shown in FIG. 2 (c).
Meanwhile, as shown in FIG. 4B, it can be seen that the measurement system using the dispersion interferometer according to the embodiment of the present invention includes a nonlinear component, and thus the directionality of the measured distance can be determined.
It can be seen that the measured distance calculated as in FIG. 4 (c) can be extended to the negative value, and the distance from the -L max value to the L max value except the dead zone is measured can do. The L min value and the L max value measured in the embodiment of the present invention were 16.8 탆 and 170.9 탆, respectively.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications may be made by those skilled in the art.
100: dispersion interferometer 110: light source
120: collimator lens 130: light splitter
140: Reference Mirror 150: Mirror to be measured
160: dispersion plate 170: spectroscope
Claims (10)
A reference mirror arranged at a position perpendicular to a path of the light, the reference mirror reflecting the light reflected from the light splitter;
A measurement object mirror arranged on the path of the light and reflecting the light transmitted through the optical splitter;
A dispersion plate arranged between the optical splitter and the reference mirror or between the optical splitter and the measurement target mirror and made of a material whose refractive index is changed according to a wavelength; And
And the light reflected from the reference mirror and reflected again by the optical splitter and the light reflected by the measuring object mirror are combined with each other to generate an interference signal for each optical frequency. And a spectroscope for detecting the light,
Characterized in that the phase of the measured optical frequency has a nonlinear component and that the direction can be discriminated.
Wherein the reference mirror and the measurement target mirror are fixedly arranged.
Wherein the dispersion plate is made of glass or fused silica.
Further comprising a collimating lens arranged between the light source and the light splitter and adapted to convert light from the light source into collimated light.
And a determination unit for measuring a distance or a thickness using the signal detected from the dispersion interferometer,
The phase of each optical frequency measured from the dispersion interferometer has a non-linear component,
Wherein the determination unit determines the directionality using the nonlinear component information and measures the distance or the thickness.
The dispersion interferometer:
A light splitter for partially reflecting and partially transmitting light from a light source;
A reference mirror arranged at a position perpendicular to a path of the light, the reference mirror reflecting the light reflected from the light splitter;
A measurement object mirror arranged on the path of the light and reflecting the light transmitted through the optical splitter;
A dispersion plate arranged between the optical splitter and the reference mirror or between the optical splitter and the measurement target mirror and made of a material whose refractive index is changed according to a wavelength; And
And the light reflected from the reference mirror and reflected again by the optical splitter and the light reflected by the measuring object mirror are combined with each other to generate an interference signal for each optical frequency. And a spectroscope for detecting the scattered light.
Wherein the reference mirror and the measurement object mirror are fixedly arranged.
Wherein the dispersion plate is made of glass or fused silica.
Wherein the dispersion interferometer further comprises a collimator lens arranged between the light source and the light splitter and converting the light from the light source into parallel light.
Wherein the phase of each optical frequency measured from the dispersion interferometer has a nonlinearity expressed by the following equation.
(Equation)
C 0 : Light speed during vacuum
L 1 : Distance between the beam splitter and the reference mirror
L 2 : Distance between the beam splitter and the target mirror
t: thickness of the dispersion plate
N d (υ): refractive index of diffuser plate
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20220040053A (en) * | 2020-09-23 | 2022-03-30 | 국방과학연구소 | System and method for generating dual entanglements of frequency bin entanglement and polarization entanglement in atomic ensemble |
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| JPH11257915A (en) * | 1998-01-29 | 1999-09-24 | Hewlett Packard Co <Hp> | Interferometer for measuring displacement |
| KR100737177B1 (en) | 2006-05-15 | 2007-07-10 | 경북대학교 산학협력단 | Interferometer using vertical-cavity surface-emitting lasers |
| JP2009186191A (en) * | 2008-02-01 | 2009-08-20 | National Institute Of Advanced Industrial & Technology | Dimension measuring device and method |
| JP5124485B2 (en) * | 2006-02-18 | 2013-01-23 | カール マール ホールディング ゲーエムベーハー | Optical surface sensor |
| KR101407482B1 (en) * | 2012-07-03 | 2014-06-16 | 한국표준과학연구원 | Apparatus and method for measuring hole shape and depth |
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Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH11257915A (en) * | 1998-01-29 | 1999-09-24 | Hewlett Packard Co <Hp> | Interferometer for measuring displacement |
| JP5124485B2 (en) * | 2006-02-18 | 2013-01-23 | カール マール ホールディング ゲーエムベーハー | Optical surface sensor |
| KR100737177B1 (en) | 2006-05-15 | 2007-07-10 | 경북대학교 산학협력단 | Interferometer using vertical-cavity surface-emitting lasers |
| JP2009186191A (en) * | 2008-02-01 | 2009-08-20 | National Institute Of Advanced Industrial & Technology | Dimension measuring device and method |
| KR101407482B1 (en) * | 2012-07-03 | 2014-06-16 | 한국표준과학연구원 | Apparatus and method for measuring hole shape and depth |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| KR20220040053A (en) * | 2020-09-23 | 2022-03-30 | 국방과학연구소 | System and method for generating dual entanglements of frequency bin entanglement and polarization entanglement in atomic ensemble |
| KR102414411B1 (en) | 2020-09-23 | 2022-06-29 | 국방과학연구소 | System and method for generating dual entanglements of frequency bin entanglement and polarization entanglement in atomic ensemble |
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