WO2021164202A1 - Système d'imagerie par tomographie à cohérence optique à double champ de vision et procédé de mesure de l'épaisseur d'un matériau - Google Patents

Système d'imagerie par tomographie à cohérence optique à double champ de vision et procédé de mesure de l'épaisseur d'un matériau Download PDF

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WO2021164202A1
WO2021164202A1 PCT/CN2020/105692 CN2020105692W WO2021164202A1 WO 2021164202 A1 WO2021164202 A1 WO 2021164202A1 CN 2020105692 W CN2020105692 W CN 2020105692W WO 2021164202 A1 WO2021164202 A1 WO 2021164202A1
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sample
light source
thickness
arm
imaging system
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PCT/CN2020/105692
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Chinese (zh)
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莫建华
吴倩
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苏州大学
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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
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
    • G01B11/0675—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating using interferometry

Definitions

  • the invention relates to the technical field of material detection, in particular to the technical field of non-transparent material thickness detection, in particular to a dual-field optical coherence tomography imaging system and a non-transparent material thickness detection method.
  • Optical coherence tomography is a low-coherence optical interference imaging technology that can scan and image optical scattering media such as biological tissues, and the obtained image resolution can reach the micron level.
  • OCT has a new type of technical means, which has the advantages of non-contact, non-invasive, non-invasive and high resolution. According to its imaging mechanism, this technology is very suitable for imaging and thickness measurement of multilayer structures. Therefore, OCT has been widely used in medical diagnosis. So far, OCT has been successfully applied to ophthalmology imaging as a routine tool in ophthalmology, and has shown great potential in clinical fields such as dermatology, cardiology, and gastroenterology.
  • OCT In many non-medical fields, OCT has also developed rapidly, especially in non-destructive testing, including non-destructive testing of paper, drug tablet coatings, jade, industrial ceramics, etc. At the same time, due to the micron-level resolution of OCT, it is also of great significance in thickness measurement and has a wide range of application prospects in the medical and industrial fields.
  • OCT In the medical field, OCT is often used to measure the thickness of the fiber layer, fiber cap and cornea.
  • OCT In the industrial field, OCT is often used for thickness measurement of PCBs, metal foils, automotive coatings, pearls, eggshells, etc.
  • Thickness is one of the measurement units of material properties, and its measurement method is also a common content in production and life.
  • the methods of measuring material thickness can be divided into contact measurement and non-contact measurement.
  • the contact measurement method mainly uses tools such as vernier calipers and spiral micrometers.
  • the measuring tool of the contact measurement method directly contacts the material to produce stress, which not only affects the measurement accuracy, but also easily scratches the surface of the material.
  • the non-contact measurement method is mainly carried out by the ultrasonic method and the eddy current method. With the development of optical technology and electronic technology, the accuracy of non-contact measurement methods is getting higher and higher, and it has become the main measurement method in the field of industrial production.
  • the ultrasonic method determines the thickness of the measured material by measuring the wave's reflected echo time in the material.
  • the ultrasonic method determines the thickness of the measured material by measuring the wave's reflected echo time in the material.
  • multiple reflected waves and transmitted waves are generated at the heterogeneous interface.
  • the echoes on the upper and lower surfaces of the medium will be mixed together, making it difficult to distinguish. This makes it difficult for conventional ultrasonic thickness measurement techniques to obtain the necessary parameters such as sound velocity and sound attenuation.
  • the eddy current method uses a certain relationship between the lift-off distance and the coating thickness, and realizes the thickness measurement through the lift-off effect.
  • OCT has better performance in both axial resolution and lateral resolution.
  • OCT is currently only used to measure the thickness of transparent materials.
  • the present invention overcomes the shortcomings of the prior art and provides a method for detecting the thickness of non-transparent materials based on swept optical coherence tomography imaging. It adopts a dual-side view OCT system to further extend the OCT technology to the thickness measurement of opaque materials. Improve the accuracy of measuring the thickness of non-transparent materials.
  • the technical solution adopted by the present invention is: a dual-field optical coherence tomography imaging system, including a scanning imaging system with a data acquisition function, and a swept frequency light source that provides a light source for the scanning imaging system.
  • the scanning imaging system adopts the DSV-OCT system.
  • the DSV-OCT system includes a sample arm and a reference arm that are respectively connected to the sweep light source, and the sweep light source provides the sample arm and the reference arm with a sampling light source or Reference light source; the sample arm is also correspondingly connected with a sample placement platform, the sample placement platform includes a posture adjustment unit for positioning the sample to be tested; the sample arm interferes with the light returned by the reference arm to form an interference signal, the The interference signal is detected by the balanced photodetector and transmitted back to the PC.
  • an optical fiber coupler 1 is arranged between the light source output end of the swept frequency light source and the sample arm and the reference arm.
  • the optical fiber coupler 1 divides the light source into a sampling light source and a reference arm. There are two light sources, and the sampling light source and the reference light source are respectively introduced into the sample arm and the reference arm.
  • the attitude adjustment unit is drivingly connected to the DSV-OCT system; the attitude adjustment unit includes one or more of an X-axis position platform, a Y-axis displacement platform, and a Z-axis displacement platform .
  • a second optical fiber coupler is arranged between the sample arm and the sample placement platform, and the second optical fiber coupler creates two sampling light sources from the sampling light source; the sample to be tested
  • the correction introduction device is arranged opposite to the two sides of the test sample, the correction introduction device includes a collimator one and a focusing lens; the two sampling light sources pass through the correction introduction device on both sides of the sample to be tested. After passing through the focusing lens, the sampling light source is provided on both sides of the sample to be tested to perform double-side imaging.
  • one end of the reference arm corresponds to the optical fiber coupler
  • the other end of the reference arm introduces a reference light source
  • the other end of the reference arm corresponds to the return device, so After the reference light source passes through the return device, the reference light source is input to the balanced photodetector.
  • the return device includes a collimator and a flat mirror that are arranged oppositely; after the reference light source is introduced into the return device, it passes through a set of two collimators and a flat mirror, and then the opposite A set of plane mirrors and a second collimator introduce the reference light source into the balanced photodetector.
  • a method for detecting the thickness of a non-transparent material in a swept optical coherence tomography imaging system :
  • Step one select and calibrate the corresponding detection system, select the DSV-OCT system, and position the sample to be tested on the posture adjustment unit of the sample placement platform;
  • Step 2 Provide a sampling light source to the sample arm through the swept frequency light source and a reference light source to the reference arm; perform data collection on the sample to be tested, and the sampling light source output after the data collection sampling light source passes through the sample to be tested;
  • Step 3 Perform B scan or/and C scan through the sample arm, sampling arm, and posture adjustment unit of the sample placement platform in the DSV-OCT system; collect and process the returned data through the PC;
  • a scan Point measurement of the sample;
  • B scan realize the one-dimensional linear scan of the light spot on the sample surface to obtain the cross-sectional view of the scanning position;
  • C scan realize the scan of the light spot on the two-dimensional area of the sample surface to obtain the three-dimensional structure of the scanning position picture;
  • Step 4 The PC converts the processed data and calculates the thickness of the sample.
  • A-scan point measurement is performed on a sample to obtain interference spectrum signals, and the structure of the sample measurement point along the depth direction can be obtained through signal processing, which is called A-scan.
  • B-scan The sample is moved at a constant speed along the x-direction through the posture adjustment unit, so as to realize a one-dimensional linear scan of the light spot on the sample surface. The acquired data can be processed to obtain a cross-sectional view of the scanning position, which is called This is B scan.
  • C-scan The posture adjustment unit makes the sample move at a constant speed along the x and y directions, so as to realize the scanning of the light spot on the two-dimensional area of the sample surface, and process the acquired data to obtain the three-dimensional structure diagram of the scanning position. This is called C-scan.
  • a method for detecting the thickness of a non-transparent material in a swept optical coherence tomography imaging system In a preferred embodiment of the present invention, a method for detecting the thickness of a non-transparent material in a swept optical coherence tomography imaging system.
  • step 2 after the sample arm creates the output sampling light source into two sampling light sources.
  • the two sampling light sources are introduced symmetrically to the opposite sides of the sample to be tested, and the reference light source returned from the reference arm is three-coupled through the fiber coupler, and then input to the balanced photodetector, interference occurs Signal, and then transmit the interference signal back to the PC.
  • a method for detecting the thickness of non-transparent materials of a dual-field optical coherence tomography imaging system In a preferred embodiment of the present invention, a method for detecting the thickness of non-transparent materials of a dual-field optical coherence tomography imaging system.
  • the thickness measurement is performed by the DSV-OCT system, and the DSV-OCT system uses the opaque material.
  • the thickness of the surface profile is measured, so it is not limited by the imaging depth;
  • the actual thickness can be calculated using the axial gap between the two surface contours in the C scan; if there is a virtual reflective surface with a thickness of 0 on the focal plane, the reflective surface displayed by two independent sampling beams will be in B There are two different depth positions in the scan, and the depths are defined as z af and z bf respectively ; if there is no sample to be measured, there is a bright horizontal line in the B scan because of the unidirectional light between the two sampling optical elements Pass, it is defined as the reference plane z rp ; the relationship between these three depths is as follows:
  • the focal plane is slightly deviated from the middle plane of the material, so the left and right surfaces will have some offsets, and the depths are z rs and z ls respectively ; the thickness can be calculated according to the following formula:
  • px represents the pixel size in the axial direction.
  • a method for detecting the thickness of a non-transparent material of a dual-field optical coherence tomography imaging system in step 4:
  • the focal plane is inside the material, but slightly deviated from the middle plane of the material, so the left and right surfaces will have some offset.
  • the left and right surfaces are on the same side of the reference plane, and the depths are z rs and z ls respectively ; according to the following formula Calculate the thickness:
  • px represents the pixel size in the axial direction
  • Method 2 The common situation of sample placement is that the focal plane is not inside the material, and the two surfaces are on different sides of the reference depth; the thickness is calculated according to the following formula:
  • the present invention solves the defects existing in the background technology, and the beneficial effects of the present invention are as follows:
  • the invention provides a new feasible and effective method for measuring the thickness of opaque materials with a dual-field optical coherence tomography imaging system.
  • a dual-field optical coherence tomography imaging system By evaluating the performance of DSV-OCT on glass slides and comparing it with traditional optical OCT, the results show that DSV-OCT maintains the imaging capabilities of OCT and has good thickness measurement capabilities for opaque materials.
  • the scheme designed by the present invention is also suitable for spectral domain optical coherence tomography imaging system.
  • this method has the following advantages: 1.
  • the method proposed in the present invention is non-contact and will not damage the surface of the material. 2. Realize objective measurement through optical imaging, which can reduce the influence of human subjective factors.
  • this method Compared with the existing non-contact measurement methods, this method has the following advantages: 1.
  • the method is non-invasive and can detect the thickness of non-transparent materials non-destructively. 2. Higher measurement accuracy. 3. Not affected by the surface roughness of the material itself.
  • Figure 1 is a schematic diagram of the DSV-OCT system
  • FIG. 2 Two-sided sampling scheme: (a) The virtual reflection plane with zero thickness is located at the focal point to obtain the reference plane; (b) and (c) are the focal planes located inside and outside the sample with thickness d, respectively.
  • the z rs line and z ls line respectively represent the left and right contours of the opaque sample, and the dashed line is the position of the reference plane.
  • Figs. 3(a) to (c) are actual B-scan images of non-transparent materials corresponding to Figs. 2(a) to (c), respectively.
  • Figure 4 (a) B-scan with DSV-OCT focal plane inside the glass slide; (b) B-scan with DSV-OCT focal plane outside the glass slide.
  • the z ls_a and z rs_a lines represent the imaging of the left surface and the right surface of the glass slide by the left sampling beam, respectively, and the z rs_b and z ls_b lines represent the imaging of the right surface and the left surface of the glass slide by the right sampling beam, respectively.
  • the L line is not used in the actual measurement. It is the signal detected after the light goes from the left beam to the right beam, or the signal is detected after the light goes from the right beam to the left beam. The two signals overlap. of.
  • Thickness C curve measured with a micrometer and thickness measured with DSV-OCT focus is on the A curve inside the sample and B curve outside the sample, and the difference between the thickness measured with a micrometer and the thickness measured by DSV-OCT (AC Curve and BC curve);
  • Figure 6 The histogram and Gaussian fitting curve of the difference in the thickness of the slide glass
  • Figure 7 (a) 3D surface profile with the focus inside the opaque material, with an area of 4mm ⁇ 4mm; (b) the OCT cross-sectional image corresponding to the area marked by the dashed line in (a);
  • Figure 8 corresponds to the top and bottom surface profile of Figure 7 (b); (b) the thickness curve calculated based on the surface profile;
  • Figure 9 Thickness structure diagram of opaque material, the focal plane is inside the opaque material
  • Figure 10 (a) Use DSV-OCT to image ten-layer frosted belt; (b) Image of ten-layer frosted belt after image fusion;
  • 1-PC machine 2-balanced photodetector, 3-fiber coupler one, 6-fiber coupler two, 7-fiber coupler three, 51-collimator one, 52-collimator two, 4 -Plane mirror, 8-focus lens, 9- sample to be tested.
  • this embodiment discloses a dual-field optical coherence tomography imaging system for achieving the above purpose, including a scanning imaging system with data acquisition function, and a swept frequency light source that provides a light source for the scanning imaging system ,
  • the scanning imaging system adopts the DSV-OCT system.
  • the DSV-OCT system includes a sample arm and a reference arm that are respectively connected to the sweep light source.
  • the sweep light source provides the sample arm and the reference arm with a sampling light source or a reference light source; the sample arm There is also a sample placement platform correspondingly connected.
  • the sample placement platform includes a posture adjustment unit for positioning the sample 9; the light returned by the sample arm and the reference arm interferes to form an interference signal.
  • the interference signal is detected by the balanced photodetector 2 and transmitted back to the PC.
  • Machine 1 is also a posture adjustment unit for positioning the sample 9; the light returned by the sample arm and the reference arm interferes to form an interference signal.
  • the interference signal is detected by the balanced photodet
  • the sample placement platform is also provided with a posture adjustment unit for placing the sample 9 to be tested.
  • the posture adjustment unit includes an X-axis electric displacement platform, a Y-axis electric displacement platform, and a Z-axis manual platform connected to the detection system.
  • the sample placement platform is connected to the DSV-OCT system drive.
  • the X-axis electric displacement platform, Y-axis electric displacement platform, and Z-axis manual stage of the sample placement platform cooperate with the sample arm and reference arm in the DSV-OCT system to create two symmetrical sampling beams to achieve dual sides Imaging lays the foundation for thickness measurement of non-transparent materials.
  • the light source output end of the swept frequency light source is provided with an optical fiber coupler 3, which divides the light source into a sampling light source and a reference light source, and the sampling light source and the reference light source are respectively introduced into the sample arm And reference arm.
  • the frequency sweep light source is preferably a frequency sweep laser light source.
  • the frequency sweep laser light source uses a center wavelength of 1310 nanometers and a wavelength range of 1249.4 nanometers to 1359.6 nanometers. As shown in Figure 1.
  • the light emitted by the swept frequency laser light source is divided into two beams through a 50:50 fiber coupler, of which 50% enters the sample arm as a sampling light source, and 50% enters the reference arm as a reference light source.
  • the calibration introduction device is arranged opposite to the two sides of the sample 9 to be tested.
  • the calibration introduction device includes a collimator 51 and a focusing lens 8; the sample arm and the sample placement platform are provided with a fiber coupling at the corresponding end
  • the second 6 and the second fiber coupler 6 create the sampling light source into two sampling light sources; both of the two sampling light sources pass through the collimator 51 in the correction introduction device on both sides of the sample 9 to be tested, and then pass through the focusing lens 8.
  • Sampling light sources are provided on both sides of the sample 9 to be tested.
  • Fiber Coupler Two 6 uses a 1 ⁇ 2 fiber coupler to create two sampling beams. Two sets of the same collimator 51 and focusing lens 8 are placed symmetrically on both sides of the sample 9 to be tested.
  • one end of the reference arm corresponds to the fiber coupler one 3
  • one end of the reference arm introduces the reference light source
  • the other end of the reference arm corresponds to the return device
  • the reference light source is input into the reference light source after passing through the calibration device Balance photodetector 2.
  • the return device includes a second collimator 52 and a flat mirror 4 that are arranged oppositely; after the reference light source is introduced into the return device, it passes through a set of two collimators 52 and a flat mirror 4, and then a set of flat mirrors 4 and a second collimator 4 opposite to each other. 52 Introduce the reference light source into the balanced photodetector 2.
  • the sample arm uses the output sampling light source as the sampling light source after passing through the sample 9 to be tested, and the reference light source output by the reference arm, the backscattered light reflected by the sample arm and the reference arm respectively passes through the optical fiber Coupler three 7, the 50/50 optical fiber coupler interferes, and the interference signal is transmitted by the balanced photodetector 2 by using a pair of vertically placed electric translation stages to fix the sample to realize the sample scanning, and then transmit it back to the PC 1.
  • the output sampling light source as the sampling light source after passing through the sample 9 to be tested
  • the reference light source output by the reference arm the backscattered light reflected by the sample arm and the reference arm respectively passes through the optical fiber Coupler three 7, the 50/50 optical fiber coupler interferes
  • the interference signal is transmitted by the balanced photodetector 2 by using a pair of vertically placed electric translation stages to fix the sample to realize the sample scanning, and then transmit it back to the PC 1.
  • a method for detecting the thickness of non-transparent materials of a dual-field optical coherence tomography imaging system a method for detecting the thickness of non-transparent materials of a dual-field optical coherence tomography imaging system
  • Step one select and calibrate the corresponding detection system, select the DSV-OCT system, and position the sample 9 to be tested on the posture adjustment unit of the sample placement platform;
  • Step 2 Sweep the frequency light source to provide the sample arm with a sampling light source and the reference arm with a reference light source; perform data collection on the sample 9 to be tested, and the data collection sample light source passes through the sample 9 to be tested and then outputs the sample light source;
  • Step 3 A scan or/and B scan or/and C scan are performed through the sample arm, sampling arm, and posture adjustment unit of the sample placement platform in the DSV-OCT system; B scan and C scan are preferred in the present invention. Collect and process the returned data through the PC 1;
  • Step 4 The PC 1 converts the processed data and calculates the thickness of the sample.
  • A-scan point measurement is performed on a sample to obtain interference spectrum signals, and the structure of the sample measurement point along the depth direction can be obtained through signal processing, which is called A-scan.
  • B-scan The sample is moved at a constant speed along the x-direction through the posture adjustment unit, so as to realize a one-dimensional linear scan of the light spot on the sample surface. The acquired data can be processed to obtain a cross-sectional view of the scanning position, which is called This is B scan.
  • C-scan The posture adjustment unit makes the sample move at a constant speed along the x and y directions, so as to realize the scanning of the light spot on the two-dimensional area of the sample surface, and process the acquired data to obtain the three-dimensional structure diagram of the scanning position. This is called C-scan.
  • a method for detecting the thickness of a non-transparent material in a swept optical coherence tomography imaging system In a preferred embodiment of the present invention, a method for detecting the thickness of a non-transparent material in a swept optical coherence tomography imaging system.
  • step 2 after the sample arm creates the output sampling light source into two sampling light sources.
  • the two sampling light sources are introduced symmetrically into the opposite sides of the sample 9 to be tested, they are coupled with the reference light source returned by the reference arm through the fiber coupler 37, and then input to the balanced photodetector 2 to generate The interference generates an interference signal, and then the interference signal is transmitted back to the PC 1.
  • a method for detecting the thickness of non-transparent materials of a dual-field optical coherence tomography imaging system In a preferred embodiment of the present invention, a method for detecting the thickness of non-transparent materials of a dual-field optical coherence tomography imaging system.
  • the thickness measurement is performed by the DSV-OCT system, and the DSV-OCT system uses the opaque material.
  • the thickness of the surface profile is measured, so it is not limited by the imaging depth;
  • the actual thickness can be calculated using the axial gap between the two surface contours in the C scan; if there is a virtual reflective surface with a thickness of 0 on the focal plane, the reflective surface displayed by two independent sampling beams will be in B There are two different depth positions in the scan, and the depths are defined as z af and z bf respectively ; if there is no sample to be measured, there is a bright horizontal line in the B scan because of the unidirectional light between the two sampling optical elements Pass, it is defined as the reference plane z rp ; the relationship between these three depths is as follows:
  • the focal plane is slightly deviated from the middle plane of the material, so the left and right surfaces will have some offsets, and the depths are z rs and z ls respectively ; the thickness can be calculated according to the following formula:
  • px represents the pixel size in the axial direction.
  • a method for detecting the thickness of a non-transparent material of a swept optical coherence tomography imaging system in step four:
  • the focal plane is inside the material, but slightly deviated from the middle plane of the material, so the left and right surfaces will have some offset.
  • the left and right surfaces are on the same side of the reference plane, and the depths are z rs and z ls respectively ; according to the following formula Calculate the thickness:
  • px represents the pixel size in the axial direction
  • Method 2 The common situation of sample placement is that the focal plane is not inside the material, and the two surfaces are on different sides of the reference depth; the thickness is calculated according to the following formula:
  • B-scan and C-scan are performed in cooperation with the sample arm in the DSV-OCT system and the posture adjustment unit of the sample placement platform through the PC 1, and data acquisition and processing are realized.
  • the PC 1 uses the external k clock provided by the laser source as the sampling clock to perform analog-to-digital conversion of the signal output by the balanced detector through the data acquisition card set up in the PC 1, and the obtained interference spectrum signal is evenly distributed in the wave number space at equal intervals and stored in Computer memory, used for subsequent Fourier transform calculations.
  • the data acquisition program is built on the LabVIEW platform to collect data and control the movement of the electric translation stage to realize B-scan and C-scan.
  • Data processing is mainly through spectral shaping, Fourier transform and removal of fixed pattern noise on the detected interference signal, thereby converting the interference signal into a signal in the depth domain of the sample.
  • FIG. 2 illustrates the mechanism of the DSV-OCT system for thickness measurement.
  • the DSV-OCT system measures thickness through the surface profile of opaque materials, so it is not limited by the imaging depth.
  • the actual thickness can be calculated using the axial gap between the two surface profiles in the same C-scan.
  • the reflective surface displayed by two independent sampling beams will be located at two different depths in the B-scan, and the depths are defined as z af and z bf respectively ; if there is no sample to be measured, then There is a bright horizontal line in the B-scan. This is due to the unidirectional passage of light between the two sampling optical elements, which is defined as the reference plane z rp ; the relationship between these three depths is as follows:
  • a material with a thickness of d is placed between the two focusing lenses 8.
  • the sample can be placed in two ways.
  • Figure 2(b) shows that the focal plane is inside the material, but it is slightly deviated from the middle plane of the material, so the left and right surfaces will have some offset.
  • the left and right surfaces are on the same side of the reference plane, and the depths are z rs and z ls respectively .
  • the thickness can be calculated according to the following formula:
  • px represents the pixel size in the axial direction
  • the reference plane passes through without placing any sample, the beam starts from one side of the sample arm and is received by the other side and is finally detected.
  • the depth position of the signal on the OCT image is used as the reference plane, as shown in Figure 3(a).
  • Figure 3 (b) and (c) are B-scans of the silica gel model collected using the DSV-OCT system, corresponding to the two situations described in Figure 2 (b) and (c). Obviously, only very shallow depth areas can be imaged from both sides of the sample 9 to be tested. Therefore, each sampled beam produces only one surface profile in a single B-scan. Moreover, the depth distribution of the two surfaces imaged in the B-scan is consistent with the theoretical prediction in Figure 2. It is worth mentioning that in the experiment, due to the inherent characteristics of the electric translation stage, the movement of the sample driven by it has a process from acceleration, uniform speed to deceleration. Since the data collected during acceleration and deceleration is not uniform, each B-scan only retains the data of the same uniform speed process.
  • the accuracy of the DSV-OCT system in the thickness measurement of the present invention uses a transparent glass slide with a thickness of about 1 mm as a sample, and compares the thickness measured using the DSV-OCT system and a micrometer.
  • Figure 4 (a) and Figure 4 (b) are the images of DSV-OCT on the glass slide.
  • the reference plane here is the same as in Figure 3 (a).
  • both sampling beams image the entire depth of the slide, which can explain the existence of four surfaces in the B scan of the DSV-OCT slide.
  • there is a bright horizontal line which is due to the unidirectional transmission of light between the two sampled optical elements.
  • Figure 4 shows the thickness calculated from (a) to (b) and the thickness obtained by averaging ten times of micrometer measurements as shown in Figure 5.
  • the internal thickness of the focal plane measured by DSV-OCT (1.01mm ⁇ 1.18 ⁇ m) and the external thickness (1.01mm ⁇ 1.14 ⁇ m) are basically the same as the average thickness measured by the micrometer (1.01mm ⁇ 1.6 ⁇ m).
  • the thickness difference curve in Figure 5 can make the difference more intuitive. It can be clearly seen from Figure 5 that the inconsistency of the two methods is close to zero in the full range of 3mm.
  • the histogram in Figure 6 illustrates the statistical data of the measurement error in Figure 5, and the A curve is a Gaussian fit of the thickness difference histogram.
  • the thickness difference between the DSV-OCT system and the micrometer ranges from -5.8 to 6.08 ⁇ m, the average difference is 0.4 ⁇ m, the standard deviation is 1.18 ⁇ m, and the FWHM of the Gaussian curve is 2.2 ⁇ m.
  • the difference range is -6.88 ⁇ 5 ⁇ m
  • the average difference is -0.28 ⁇ m
  • the standard deviation is 1.14 ⁇ m
  • the FWHM of the Gaussian curve is 2.2 ⁇ m.
  • the DSV-OCT system has the ability to generate a two-dimensional thickness map.
  • a 4mm square area was scanned with the DSV-OCT system, and the scanned original 3D image is shown in Figure 7 (a).
  • FIG. 7(b) is an example of a cross-sectional image at the dotted rectangle frame in FIG. 7(a).
  • mean filtering is used to further reduce noise.
  • Figure 8 (a) plots the contours of the two surfaces, and the material thickness calculated using formula (4) is shown in Figure 8 (b). There are some slight fluctuations in the thickness, indicating that the surface roughness of the material is not very good.
  • Figure 10 (a) is an image of a 10-layer frosted belt generated by DSV-OCT.
  • the two sample arms have a good signal-to-noise ratio, but neither can image more than the first 4 to 5 layers.
  • Figure 10 (b) by selecting the region of interest from the generated image and then fusing, the ten-layer image of the entire matte tape can be clearly seen, as shown in Figure 10 (b).
  • the results show that the developed DSV-OCT system maintains the imaging capabilities of OCT and can provide thickness measurement of opaque materials, and the DSV-OCT system can also overcome the limitations of penetration depth and focus depth to achieve thick and weak scattering materials Full-depth imaging.

Abstract

La présente invention concerne un système d'imagerie par tomographie à cohérence optique à double champ de vision et un procédé de mesure de l'épaisseur d'un matériau. Le système d'imagerie par tomographie à cohérence optique à fréquence balayée comprend un système d'imagerie à balayage, et une source de lumière à fréquence balayée servant à fournir une source de lumière au système d'imagerie à balayage ; le système d'imagerie à balayage utilise un système DSV-OCT qui comprend un bras d'échantillon et un bras de référence qui sont respectivement connectés de manière correspondante à la source de lumière à fréquence balayée ; et la source de lumière à fréquence balayée fournit une source de lumière d'échantillonnage ou une source de lumière de référence, respectivement pour le bras d'échantillon et le bras de référence. Le bras d'échantillon est en outre pourvu d'une plateforme de placement d'échantillon qui comprend une unité de réglage d'attitude pour positionner un échantillon à mesurer ; et les lumières renvoyées par le bras d'échantillon et le bras de référence interfèrent l'une avec l'autre pour former un signal d'interférence qui est détecté par un photodétecteur équilibré et renvoyé à un PC. La présente invention concerne un système OCT à double vision qui étend la technologie OCT à la mesure d'épaisseur de matériaux opaques, ce qui permet d'améliorer la précision de la mesure de l'épaisseur de matériaux opaques.
PCT/CN2020/105692 2020-02-21 2020-07-30 Système d'imagerie par tomographie à cohérence optique à double champ de vision et procédé de mesure de l'épaisseur d'un matériau WO2021164202A1 (fr)

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