KR101527601B1 - optical-phase imaging system and method thereof - Google Patents

Abstract

The present invention relates to an optical phase measuring system. The system includes a light source part emitting light; a band dividing part generating dividing light dividing the light from the light source part into a plurality of bandwidths and phase inversion light having a phase inversed against the dividing light, and outputting the dividing light and the phase inversion light through different routes; a delay part installed on the output route of the dividing light or output route of the phase inversion light to delay transmission time so that the dividing light and the phase inversion light do not interfere in each other; and a processing part radiating the light, directly discharged from the band dividing part, and the light, delayed and discharged from the band dividing part through the delay part, to a measurement object, and detecting and processing the light, reflected from the measurement object. According to the optical phase measuring system and a measuring method thereof, the resolution of the measurement object increases by using three separated spectrums having the same phase noise and bandwidth as two separated spectrums dividing the bandwidth of the light source.

Description

[0001] The present invention relates to a phase-optical measurement system,

The present invention relates to a phase light measurement system and a measurement method thereof, and more particularly, to a phase light measurement system and a measurement method thereof that can increase measurement accuracy while increasing the number of divided spectra with respect to a wavelength bandwidth of a light source.

The optical phase measurement system that measures and images the phase change of the light incident on the object to be measured can exhibit a resolution exceeding the optical diffraction limit, so that the research and development has been made steadily.

Such phase light measurement methods include a phase contrast method, a phase-shifting method, a digital holography method, a Fourier phase microscopy method, a light interference phase microscope optical coherence phase microscopy).

All of these optical phase measurements have phase wrapping (2π ambiguity) problems.

That is, in a phase measurement method having a geometrical optical structure for measuring light reflected from a probe stage, the phase value ?? of light to be measured has a relationship expressed by Equation 1 below when converted into a sample change amount? Z.

Where λ ₀ is the center wavelength of the light source used, and n is the average refractive index between the reference end and the sample end. In this case, since the measured phase value ranges from 0 to 2 [radian], there is a problem that the maximum measurement range is limited to about 1 탆.

To solve this phase wrapping, a software algorithm or a hardware configuration is used. The most commonly used method is a simple phase unwrapping algorithm, which adds or subtracts 2π each time a jump of the measured phase value occurs. This is problematic because the same amount is added and subtracted by 2 n π when the jump occurs.

Other software approaches are not as efficient as complex algorithms and many operations, and the hardware approach complicates setup, including additional optics and measurement stages.

In order to solve these problems, a phase measurement method using multi-wavelengths has been proposed, which can obtain a new long wavelength that can replace the central wavelength λ ₀ of the above relation, thereby increasing the maximum measurement range of the sample variation amount Δz .

Korean Patent No. 10-1308433 proposed by the present inventor for such a multi-wavelength measuring method uses a band-split light obtained by dividing the bandwidth of a light source.

In other words, we divide the total bandwidth into two or more parts, measure the phase for each divided bandwidth, and then obtain new wavelengths from it and increase the overall measurement range.

However, in the case of the spectrum division method of such a light source, since it is divided within the bandwidth of the light emitted from the light source, the processing range is increased by repeating the processing method as the divided part of the bandwidth increases. However, There is a disadvantage that the bandwidth that can be used becomes narrow.

This results in a decrease in resolution, which is the smallest measurable range, as a result of studies showing that phase noise increases with narrow bandwidth.

That is, as the measurement range increases, the phase noise increases and the resolution decreases. If the center wavelengths of the respective spectra are represented by? ₁ and? ₂ on the two divided spectra, the new increased center wavelength? Can be expressed by the following equation (2).

According to Equation (2), as the interval between two central wavelengths is narrowed, the new central wavelength? Increases and the range in which the sample variation? Z increases can be increased.

However, according to the conventional spectrum division method, in order to narrow the two central wavelength intervals, the intervals of the divided spectrums must be narrowed. In this case, there is a problem that the phase noise increases as much as possible.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a phase light measuring system and a measuring method thereof, which can increase resolution without increasing phase noise.

According to an aspect of the present invention, there is provided a phase light measuring system comprising: a light source for emitting light; A band splitter for dividing a bandwidth of the light emitted from the light source into a plurality of bandwidths and a phase inverted light inverted in phase with respect to the split light and for outputting the split light and the phase inverted light in different paths A division section; A delay unit which is provided on the output path of the split light or the output path of the phase inversion light so as to prevent the split light and the phase inversion light from interfering with each other and outputs the delayed transmission time; And a processing unit for irradiating the light to be measured with the light directly output from the band dividing unit and the light delayed and output from the band dividing unit through the delay unit and detecting and processing the light reflected from the measurement target.

Preferably, the delay portion is provided on the output path of the phase inversion light.

The band dividing unit may divide the light input through the first input end from the light source unit through the first output end and the second output end, and may divide the first output end and the second output end, And outputs the first divided light and the second divided light obtained by band-dividing the light of the band emitted from the light source unit through the birefringent portion and outputting through the third output end, and outputs the first divided light and the second divided light, A band-split interferometer for outputting phase-inverted light whose phase is inverted with respect to light through the first input terminal; And an optical path adjusting unit for causing the light emitted from the light source unit to enter the first input end and causing the phase inversion light output from the first input end to enter the delay unit.

Preferably, the processing unit includes: a second optical coupler receiving the first and second split lights output from the third output terminal and the phase inverted light output from the delay unit and outputting the received phase inversion through the relay terminal; A probe unit for irradiating light transmitted to the measurement object and transmitting the light reflected from the measurement object backward; A third optical coupler for receiving light output from the second optical coupler, transmitting the light through the probe unit, and outputting the light incident through the probe unit to a main detection end; A light detecting unit connected to the main detecting unit and detecting light incident thereon; And a measurement unit that acquires information on the measurement target object from the signal output from the optical detection unit.

According to another aspect of the present invention, there is provided a phase light measuring method comprising: Generating split light obtained by dividing a band of light emitted from the light source part and phase inverted light that is phase-inverted with respect to the split light; I. Outputting the divided light and the phase inverted light to a measurement object through a probe unit with a time difference so as not to interfere with each other; All. And a step of acquiring information of the measurement object by detecting light reflected by the measurement object and entering through the probe unit.

Preferably, in the step (c), a sagnac interferometer for generating a first divided light and a second divided light obtained by dividing a band of light emitted from the light source part into two is applied. The first split light of claim 1 and the center wavelength (λ _1), the second split light the third center wavelength (λ ₃₎ and the phase shift of light the second center wavelength corresponding to a first center wavelength of (λ ₂₎ Obtaining a first image difference value (Z ₁₃ ) from a phase difference ( ₁₃ ) of a first phase image (Z ₁ ) and a third phase image (Z ₃ ) corresponding to a third central wavelength; All-2. The phase shift of light the second center wavelength (λ ₂₎ a second phase image (Z ₁₎ and the third phase image (Z ₃₎ the phase difference between the second image difference (Z ₂₃₎ from (φ ₂₃₎ in response to ; All three. And determining a final image by obtaining a third image difference value (Z _13-23 ) from a phase difference between the first image difference value and the second image difference value.

According to the phase light measuring system and the measuring method thereof according to the present invention, it is possible to use three separate spectra having the same phase noise and bandwidth as the two separated spectra for equally dividing the bandwidth of the light source, It also offers the advantage of being able to increase further.

1 is a view showing a phase light measurement system according to the present invention,
FIG. 2 is a graph for explaining light generated by the band dividing unit in the light emitted from the light source unit of FIG. 1,
FIG. 3 is a view for explaining a pattern in which light generated by the band division unit of FIG. 1 is transmitted without being superimposed,
FIG. 4 is a graph showing a result of measuring a spectrum generated by the band division unit of FIG. 1,
FIG. 5 is a graph showing a result of measurement on a time axis after passing through a probe unit capable of generating an interference signal using only a signal output through the third output terminal of FIG. 1,
FIG. 6 is a graph showing a result of measurement on a time axis after passing through a probe unit capable of generating an interference signal using a signal output from the output terminal of the second optical coupler of FIG. 1,
7 is a graph showing an enlarged part of the light emission period in FIG.

Hereinafter, a phase light measuring system and a measuring method thereof according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing a phase light measurement system according to the present invention.

Referring to FIG. 1, the phase light measuring system 100 includes a light source 110, a band dividing unit 120, a delay unit 141, and a processing unit 160.

The light source 110 is a light source that emits light having a bandwidth.

The light source unit 110 may be a wavelength variable light source that outputs light while varying wavelengths at a predetermined cycle, or a broadband light source that simultaneously outputs light having a wide range of wavelengths.

The band dividing unit 120 generates split light obtained by dividing the bandwidth of the light emitted from the light source unit 110 into a plurality of bandwidths and phase inversed light whose phase is inverted with respect to the split light, And outputs it to another path.

The band division unit 120 includes a band division interferometer and an optical circulator 127.

The band split interferometer is configured to split the light input from the light source unit 110 through the first input end 131 of the first optical coupler 130 through the optical circulator 127 into the first output end 132 and the second output end 133, And passes through the birefringent element 135 made of a birefringent material and passes through the loop that connects the first output terminal 132 and the second output terminal 133 to the band emitted from the light source unit 110 And outputs the phase-inverted light, which is phase-inverted with respect to the first split light and the second split light, to the first And can be output through the input terminal 131.

The band split interferometer includes a first optical coupler 130, a first optical fiber 136, a second optical fiber 137, and a polarization controller 138.

The first optical coupler 130 has a first input terminal 131 and a third output terminal 134 on one side and a first output terminal 132 and a second output terminal 133 on the other side.

Here, the light output through the third output end 134 outputs the first split light and the second split light, which divide the band of the light output from the light source 110 into two bands, And outputs the phase-inverted phase-inverted light that is phase-inverted with respect to the first divided light and the second divided light.

 The first optical fiber 136 is connected between the first output end 136 and one end of the birefringent portion 135 and the second optical fiber 137 is connected between the second output end 133 and the other end of the birefringent portion 135 And the polarization controller 138 is provided on the extension path of the second optical fiber 137. [

The band split interferometer is a Sagn optical interferometer that divides the light input through the first input end 131 into a first output end 132 and a second output end 133 and outputs the branched light to the first output end 132 and the second output end 133. [ Through the first input terminal 131 and the third output terminal 134, the light incident backward through the first input terminal 133 and the second input terminal 131, respectively.

The optical circulator 127 is used as an optical path adjusting unit and is disposed between the light source unit 110 and the first input terminal 131 of the first optical coupler 130 to transmit light emitted from the light source unit 110 to the first input terminal 131, So that the phase inverted light output from the first input terminal 131 is made incident on the delay unit 141. [

The delay unit 141 may be provided so as to delay the transmission time by being provided on the output path of the divided light or the output path of the phase inverted light so that the first and second divided lights and the phase inverted light do not interfere with each other in time, In the example, it is provided on the output side of the optical circulator 127 which is the output path of the phase inverted light.

That is, the delay unit 141 is connected between the optical circulator 127 and the second optical coupler 161 to transmit light, and the first delay unit 141 is connected to the first optical coupler 161 from the third output end 124, A delayed optical fiber with a longer path than the optical path was applied.

Here, the delay unit 141 may be applied with an appropriate delay time so that the first and second split lights are input to the second optical coupler 161, which will be described later, and the phase inversed light delayed by time is input.

2, when the light output from the light source unit 110 is output to the light S having the same band as that of FIG. 2A, the light is divided into a plurality of sub- The first and second split lights P1 and P3 for dividing the wavelength band of the light source unit 110 into two are generated and output through the third output stage 134 and the first and second split lights P1 and P2 The phase inverted light P2 whose phase is inverted by 180 degrees is output through the first input terminal 131 as shown in FIG. 2C. If the portion of the phase inverted light P2 having the Gaussian distribution is matched with the first divided light P1 and the second divided light P3 in the wavelength band, And three Gaussian-type band-split light beams having different wavelengths in a center wavelength range are distributed so that some wavelength bands are overlapped with each other.

Accordingly, when the phase inverted light P2 in which the wavelength bands are overlapped is temporally delayed, the light for three sub-bands can be used on the time axis, and as shown in Fig. 3A, the light amount in the light source unit 110 The first and second divided lights P1 and P3 are outputted through the third output end 134 at the light output period Ta when the light output period for outputting the light of the first light emitting period Ta is Ta, Similarly, the phase inverted light P2 is also output through the first input terminal 131. [ Here, only the phase inverted light P2 has a Gaussian distribution.

Since the phase inverted light P2 is delayed by the delay time d as shown in FIG. 3C through the delay unit 141, the second optical coupler 161 is provided with a light emission period Ta The first divided light P1, the second divided light P3, and the phase inverted light P2 are repeatedly generated in the three bands having a Gaussian distribution and a mutual separation along the time axis.

Experimental results for such a split backlit light generating structure are shown in Figs. 4-7.

FIG. 4 is a graph showing a result of measuring a spectrum generated by the band division unit of FIG. 1 with respect to a wavelength, and FIG. 5 is a graph showing a result of the output of the third output stage 134 when a light emission period is 20 μs FIGS. 6 and 7 are graphs showing the results of measurement on the time axis after passing through the probe unit which is capable of generating only the interference signal. FIG. 6 and FIG. 7 are graphs showing the results of the signals output from the output terminal of the second optical coupler 161a FIG. 2 is a graph showing the results measured on a time axis after passing through a probe section. FIG.

4 to 7, the first split light P1, the second split light P3, and the phase inverted light P2 are generated so as to be separated from each other on the time axis.

The processing unit 160 irradiates the measurement object 200 with light output directly from the band dividing unit 120 and light delayed and output from the band dividing unit 120 through the delay unit 141, And detects and processes the light.

The processing unit 160 includes a second optical coupler 161, a third optical coupler 163, a probe unit 165, a photodetector unit 170, and a measurement unit 180.

The second optical coupler 161 receives the first and second split lights P1 and P3 output from the third output terminal 134 and the phase inverted light P2 output from the delay unit 141 And outputs it through the relay terminal 161a.

The third optical coupler 163 outputs the first divided light P1, the second divided light P3 and the phase inverted light P2 sequentially outputted through the relay terminal 161a of the second optical coupler 161 And transmits the light through the probe unit 165 and outputs the light incident through the probe unit 165 to the main detection stage 163a.

It is a matter of course that the third optical coupler 163 can be applied to the optical circulator.

The probe unit 165 irradiates light transmitted through the third optical coupler 163 to the measurement object 200 and can transmit the light reflected from the measurement object 200 inversely.

The probe unit 165 includes a plurality of lenses arranged in a housing (not shown) for converting the light emitted from the optical fiber extending from the third optical coupler 163 into parallel light and converging the parallel light onto the measurement target object 200, And a partial reflection plate 167 for transmitting a part of the focused light to be irradiated to the measurement object 200 and reflecting a part of the light to generate an interference light.

The photodetector 170 is connected to the main detection stage 163a of the third optical coupler 162 and detects the incident light and outputs an electrical signal corresponding to the detected light to the measuring unit 180. [

The photodetector 170 may be a spectrometer when a photodiode is applied when the light source 110 is a variable wavelength light source and when a broadband light source that emits light having a bandwidth is applied.

The measurement unit 180 acquires information about the measurement object 200 from the signal output from the light detection unit 170. [

The measuring unit 180 measures the first center wavelength lambda 1 of the first divided light P1 and the third central wavelength lambda 3 of the second divided light P3 and the phase inverted light P2 ) the phase values for the same position of the second center wavelength (λ2) measuring target object (200) for each (φ _1), (φ _2), (φ ₃₎ with the obtained from the optical detector 170 and acquires phase of And generates image information of the measurement target object 200 through calculation.

The calculation process of the measuring unit 180 will be described below.

The measurement unit 180 first calculates the first phase image Z ₁ and the third center wavelength? 3 with respect to the Z axis direction perpendicular to the surface of the measurement object 200 corresponding to the first center wavelength? corresponding a third phase difference between the phase image _{(Z 3) (φ 13 =} φ 1 -φ 3)) the first image is obtained a difference value (Z ₁₃₎ from.

That is, first, three divided spectrums are separated on the basis of a central wavelength known to each of the first split light P1, the second split light P3, and the phase inverted light P2.

Next, Fourier transform is performed on each separated spectrum, and a phase value of a peak corresponding to the measurement object 200 is extracted.

Through this process, phase data for three central wavelengths are obtained.

Thereafter, a difference (Z ₁ -Z ₃ ) between the first and third phase images corresponding to the central wavelengths λ ₁ and λ ₃ of the first divided light P1 and the second divided light P3, ₁₃ . If the difference is less than 0, then add 2π.

The new phase image Z ₁₃ corresponds to the phase profile by the new wavelength Λ ₁₃ (λ ₁ λ ₃ / λ ₁ -λ ₃ 1) as shown in Equations (1) and (2) and can be expressed by Equation (3) as follows.

By the same way as the measurement unit 180 phase difference between the second phase image (Z ₂₎ and the third phase image (Z ₃₎ corresponding to a second center wavelength (λ ₂₎ of the phase-inverted light (P2) (φ ₂₃ ) from the second image difference value (Z ₂₃ ).

That is, the relationship between the second and third new phase image Z ₂₃ new wavelength Λ ₂₃ from the phase difference between the phase image _{(φ 23) (λ 2 λ3} / lλ 2 -λ 3 l) corresponding to λ _2, λ ₃ Can be obtained by the following equation (4).

In addition, the measurement unit 180, obtain a first image difference (Z ₁₃₎ and a second phase difference between the third image value (Z _13-23) from the difference image difference (Z ₂₃₎ determines the final image.

Here, the third image difference value corresponds to the image information of the measurement target object 200 to be obtained.

That is, a new phase image Z _13-23 is obtained again from the previously calculated phase difference ( _13-23 ) between Z ₁₃ and Z ₂₃ . This image can be computed with the new wavelength Λ _13-23 (Λ ₁₃ Λ ₂₃ / lΛ ₁₃ -Λ ₂₃ l), and the result is the same as Λ ₁₂ . That is, the phase image Z _{13 -23} is expressed by Equation (5) below.

Preferably, the phase image Z _{13 -23} obtains an integer multiple of Λ ₁₃ and adds the result to the phase image Z ₁₃ to obtain a final phase image (Z _final ). If the time Z ₁₃ and _-23 compared to the _final Z, the difference is greater than ₁₃ or smaller than Λ in addition it gives the Λ _13.

Therefore, the final image (Z _final ) has the noise level equal to Z _13, and the maximum measurement range is Λ ₁₂ / 2m (m is a natural number). Since the new wavelength Λ ₁₂ is larger than the wavelength Λ ₁₃ when two divisions are performed, the measurable range increases without phase wrapping, and the noise level is the same as Λ ₁₃ .

The phase optical measuring system 100 includes a phase-inverted phase inversion optical system 100 and a phase-inverted phase-reversal optical system 100 in addition to the first divided light P1 and the second divided light P3, which are obtained by dividing the band into equal halves with respect to the wavelength band of the light output from the light source unit 100. [ (P2) can be obtained, thereby providing an advantage that the measurement range is expanded and the phase noise is not increased.

That is, as compared with the case where the light emitted from the light source unit 110 is simply divided into two by the spectral division method as described above, the divided light can be used without being reduced in the divided bandwidth and divided into three spectrums, Can be increased without increasing the resolution.

5 through 7, the first divided light P1, the second divided light P3, and the phase inverted light P2, which are output in the Gaussian distribution form in the second optical coupler 161, The respective bandwidths are all the same, and the separated bands have different central wavelengths (? ₁ ,? ₂ ,? ₃ ). Each bandwidth can be controlled by a path difference caused by the length of the birefringent portion 135 in the Sagnac interferometer. Each center wavelength can also be varied through a polarization controller 138 in the Sagnac interferometer.

Thus, according to the present invention, a new central wavelength? Can be simply calculated from the central wavelength of the split and phase-inverted light, and the new central wavelength? Can have a longer wavelength than the light source with two separate spectra, Noise remains at the same level as in the case of two separate spectra.

In addition, since the light having a spectrum already separated in the light source unit 110 is used, the interferometer and the measurement unit can use the conventional phase-optical meter as it is, which simplifies the measurement.

In addition, the time required to measure light with three separate spectra is the same as in the past, and the algorithm after that is simple, minimizing the calculation burden on the measuring unit.

Further, by adjusting the polarization controller 138, it is possible to change the center wavelength of the three spectra, and the measurement range can be easily changed.

110: light source unit 120:
141: delay unit 160:

Claims (10)

A light source unit for emitting light;
A band splitter for dividing a bandwidth of the light emitted from the light source into a plurality of bandwidths and a phase inverted light inverted in phase with respect to the split light and for outputting the split light and the phase inverted light in different paths A division section;
A delay unit which is provided on the output path of the split light or the output path of the phase inversion light so as to prevent the split light and the phase inversion light from interfering with each other and outputs the delayed transmission time;
And a processing unit for irradiating the measurement object with light output directly from the band division unit and light output from the band division unit through the delay unit and delayed and output, and detecting and processing the light reflected from the measurement target object Phase optical measurement system. The apparatus of claim 1, wherein the delay unit
And the phase-inverted light is provided on the output path of the phase-inverted light. 3. The apparatus of claim 2, wherein the band dividing unit
And a second birefringent element disposed on the loop for connecting the first output terminal and the second output terminal to each other through a birefringent element made of a birefringent material, And outputs the first divided light and the second divided light obtained by band-dividing the light of the band emitted from the light source unit through the third output terminal while passing through the first output port and the second divided light, And outputting the phase inverted light through the first input terminal;
And an optical path adjustment unit for causing the light emitted from the light source unit to be incident on the first input end and causing the phase inversion light output from the first input end to be incident on the delay unit. 4. The apparatus of claim 3, wherein the band-
A first optical coupler having the first input terminal and the third output terminal on one side and the first output terminal and the second output terminal on the other side;
A first optical fiber connected between the first output end and one end of the birefringent portion;
A second optical fiber connected between the second output terminal and the other end of the birefringent portion;
And a polarization controller provided on the second optical fiber,
Wherein the optical path adjusting unit is applied with an optical circulator. 4. The apparatus of claim 3, wherein the processing unit
A second optical coupler receiving the first and second split lights output from the third output terminal and the phase inverted light output from the delay unit and outputting the same through the relay terminal;
A probe unit for irradiating light transmitted to the measurement object and transmitting the light reflected from the measurement object backward;
A third optical coupler for receiving light output from the second optical coupler, transmitting the light through the probe unit, and outputting the light incident through the probe unit to a main detection end;
A light detecting unit connected to the main detecting unit and detecting light incident thereon;
And a measuring unit that obtains information on a measurement target object from a signal output from the optical detection unit. 6. The apparatus according to claim 5, wherein the optical path adjusting unit is a broadcaster,
And the delay unit is formed of a delay optical fiber that is connected between the optical circulator and the second optical coupler and transmits light and has a longer path than the first optical path extending from the third output end to the second optical coupler Phase optical measurement system. 6. The method of claim 5,
Wherein the light source unit is a wavelength variable light source that outputs light having a variable wavelength with time,
Wherein the photodetector is a photodiode. 6. The method of claim 5,
Wherein the light source unit is a broadband light source that emits light having a bandwidth,
Wherein the optical detector is a spectrometer. end. Generating split light obtained by dividing a band of light emitted from the light source part and phase inverted light that is phase-inverted with respect to the split light;
I. Outputting the divided light and the phase inverted light to a measurement object through a probe unit with a time difference so as not to interfere with each other;
All. And obtaining information of the measurement target by detecting light reflected by the measurement target object and entering through the probe unit. The method as claimed in claim 9, wherein the step (c) comprises the steps of: (a) applying a sagnac interferometer for generating first and second divided beams, which are obtained by dividing a band of light emitted from the light source,
The multi-
All-1. The first split light of claim 1 and the center wavelength (λ _1), the second split light the third center wavelength (λ ₃₎ and the phase shift of light the second center wavelength corresponding to a first center wavelength of (λ ₂₎ Obtaining a first image difference value (Z ₁₃ ) from a phase difference ( ₁₃ ) of a first phase image (Z ₁ ) and a third phase image (Z ₃ ) corresponding to a third central wavelength;
All-2. The phase shift of light the second center wavelength (λ ₂₎ a second phase image (Z ₁₎ and the third phase image (Z ₃₎ the phase difference between the second image difference (Z ₂₃₎ from (φ ₂₃₎ in response to ;
All three. And determining a final image by obtaining a third image difference value (Z _13-23 ) from a phase difference between the first image difference value and the second image difference value.

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