WO2021164202A1

WO2021164202A1 - Dual-field-of-view optical coherence tomography imaging system and material thickness measurement method

Info

Publication number: WO2021164202A1
Application number: PCT/CN2020/105692
Authority: WO
Inventors: 莫建华; 吴倩
Original assignee: 苏州大学
Priority date: 2020-02-21
Filing date: 2020-07-30
Publication date: 2021-08-26
Also published as: CN111288902A; CN111288902B

Abstract

The present invention relates to a dual-field-of-view optical coherence tomography imaging system and a material thickness measurement method. The swept-frequency optical coherence tomography imaging system comprises a scanning imaging system, and a swept-frequency light source for providing a light source for the scanning imaging system; the scanning imaging system uses a DSV-OCT system, which comprises a sample arm and a reference arm that are respectively connected correspondingly to the swept-frequency light source; and the swept-frequency light source provides a sampling light source or a reference light source for the sample arm and the reference arm respectively. The sample arm is further correspondingly provided with a sample placement platform, which comprises an attitude adjusting unit for positioning a sample to be measured; and lights returned by the sample arm and the reference arm interfere with other to form an interference signal, which is detected by a balanced photodetector and transmitted back to a PC. Provided in the present invention is a dual-side-view OCT system, which further extends the OCT technology to the thickness measurement of opaque materials, thereby improving the precision of measuring the thickness of opaque materials.

Description

A dual-field optical coherence tomography imaging system and material thickness detection method

Technical field

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.

Background technique

Optical coherence tomography (Optical Coherence Tomography, OCT) 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. 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. In the medical field, OCT is often used to measure the thickness of the fiber layer, fiber cap and cornea. In the industrial field, OCT is often used for thickness measurement of PCBs, metal foils, automotive coatings, pearls, eggshells, etc.

In other fields, there are also many methods for measuring material thickness. Thickness is one of the measurement units of material properties, and its measurement method is also a common content in production and life. Currently, 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. However, 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. However, when ultrasonic waves are incident on the multilayer medium, multiple reflected waves and transmitted waves are generated at the heterogeneous interface. When the thickness of the material is thin, 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. However, the eddy current method is greatly affected by the surface roughness of the material, and the attached substance between the material surface and the probe must be removed to eliminate the systematic and accidental errors caused by the rough surface. Therefore, it is very necessary to develop a material thickness measurement method with stronger robustness and higher accuracy. Compared with these methods, OCT has better performance in both axial resolution and lateral resolution. However, due to the limited imaging depth, OCT is currently only used to measure the thickness of transparent materials.

Summary of the invention

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.

In order to achieve the above objective, 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.

In a preferred embodiment of the present invention, 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.

In a preferred embodiment of the present invention, 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 .

In a preferred embodiment of the present invention, 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.

In a preferred embodiment of the present invention, one end of the reference arm corresponds to the optical fiber coupler, the other end of the reference arm introduces a reference light source, and 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.

In a preferred embodiment of the present invention, 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.

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 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.

Specifically, 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.

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. In step 2, after the sample arm creates the output sampling light source into two sampling light sources, After 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.

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. In step 4, 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:

d=[(z _bf -z _rs )+(z _af -z _ls )]×px; formula (2)

Among them, px represents the pixel size in the axial direction.

In a preferred embodiment of the present invention, a method for detecting the thickness of a non-transparent material of a dual-field optical coherence tomography imaging system, in step 4:

Place the material with thickness d between the two focusing lenses. At this time, there are two ways to place the sample;

Method one, 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:

d=[(z _bf -z _rs )+(z _af -z _ls )]×px; formula (2)

Among them, 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:

d=[(z _bf -z _rs )-(z _ls -z _af )]×px; formula (3)

Formulas (2) and (3) can be restated in the same form

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. 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.

Compared with the existing contact measurement method, 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.

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.

Description of the drawings

The present invention will be further described below in conjunction with the drawings and embodiments.

Figure 1 is a schematic diagram of the DSV-OCT system;

Figure 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.

Figure 5 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 (a) 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;

Among them, 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.

Detailed ways

In order for those skilled in the art to better understand the patent of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

The embodiments described below are only a part of the embodiments of the present invention, not all the embodiments; based on the embodiments of the present invention, other embodiments obtained by those of ordinary skill in the art without creative work , All belong to the protection scope of the present invention.

As shown in Fig. 1, 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.

Specifically, 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.

In a preferred embodiment of the present invention, 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.

In a preferred embodiment of the present invention, 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.

In a preferred embodiment of the present invention, 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, and 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.

In a preferred embodiment of the present invention, 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. Thereby providing B-scan and C-scan.

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,

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.

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. In step 2, after the sample arm creates the output sampling light source into two sampling light sources, After 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.

d=[(z _bf -z _rs )+(z _af -z _ls )]×px; formula (2)

Among them, px represents the pixel size in the axial direction.

In a preferred embodiment of the present invention, a method for detecting the thickness of a non-transparent material of a swept optical coherence tomography imaging system, in step four:

Place a material with a thickness of d between the two focusing lenses 8. At this time, there are two ways to place the sample;

d=[(z _bf -z _rs )+(z _af -z _ls )]×px; formula (2)

Among them, px represents the pixel size in the axial direction;

d=[(z _bf -z _rs )-(z _ls -z _af )]×px; formula (3)

Formulas (2) and (3) can be restated in the same form

Example one

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.

Specifically, the thickness is calculated. Figure 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. As shown in Figure 2(a), 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:

Then, a material with a thickness of d is placed between the two focusing lenses 8. At this time, 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} . Finally, the thickness can be calculated according to the following formula:

d=[(z _bf -z _rs )+(z _af -z _ls )]×px; formula (2)

Among them, px represents the pixel size in the axial direction;

Another common situation for sample placement is that the focal plane is not inside the material, and the two surfaces are on different sides of the reference depth, as shown in Figure 2(c). The thickness is calculated according to the following formula:

d=[(z _bf -z _rs )-(z _ls -z _af )]×px; formula (3)

Formulas (2) and (3) can be restated in the same form

In the experiment, 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). At the same time, 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. In addition, in DSV-OCT system imaging, there is a bright horizontal line, which is due to the unidirectional transmission of light between the two sampled optical elements.

Calculate the optical thickness of the glass slide according to the previously discussed thickness theory. 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. In general, the internal thickness of the focal plane measured by DSV-OCT (1.01mm±1.18μm) and the external thickness (1.01mm±1.14μm) are basically the same as the average thickness measured by the micrometer (1.01mm±1.6μm). However, there are still some subtle differences. 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. When the focal plane is inside the glass slide, the thickness difference between the DSV-OCT system and the micrometer ranges from -5.8 to 6.08 μm, the average difference is 0.4 μm, the standard deviation is 1.18 μm, and the FWHM of the Gaussian curve is 2.2 μm. When the focal plane is outside the glass slide, the difference range is -6.88～5μm, the average difference is -0.28μm, the standard deviation is 1.14μm, and the FWHM of the Gaussian curve is 2.2μm. Finally, assuming that the true value of each measurement is within the range of ±ε, the probability is 95%, and ε is defined as absolute accuracy. We quantify the performance of DSV-OCT by calculating ε. It can be seen from Figure 6 that the absolute accuracy calculated by DSV-OCT is about 3μm.

Example two

On the basis of the first embodiment, the DSV-OCT system has the ability to generate a two-dimensional thickness map. Customize a 1-inch opaque disk engraved with a circular wall (inner diameter: 2mm, outer diameter: 3mm, height: 0.3mm) as a sample. A 4mm square area was scanned with the DSV-OCT system, and the scanned original 3D image is shown in Figure 7 (a). The overall outline of the two surfaces can be clearly seen from the three-dimensional graphics. FIG. 7(b) is an example of a cross-sectional image at the dotted rectangle frame in FIG. 7(a). Before calculating the thickness, 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.

In addition, the DSV-OCT system has the potential to increase imaging depth. 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. In contrast, 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).

In general, 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.

The above is based on the ideal embodiment of the present invention as inspiration. Through the above description, relevant personnel can make various changes and modifications without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the content of the description, and the technical scope must be determined according to the scope of the claims.

Claims

A dual-field optical coherence tomography imaging system, comprising 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, characterized in that the scanning imaging system adopts a DSV-OCT system, The DSV-OCT system includes a sample arm and a reference arm that are respectively connected to the swept frequency light source, and the swept frequency light source provides a sampling light source or a reference light source to the sample arm and the reference arm, respectively; the sample arm also corresponds to Connected with a sample placement platform, the sample placement platform includes a posture adjustment unit for positioning the sample to be tested; the light returned by the sample arm interferes with the reference arm to form an interference signal, and the interference signal is detected and combined by a balanced photodetector. Send back to the PC.
A dual-field optical coherence tomography imaging system according to claim 1, wherein a fiber coupler is provided between the light source output end of the swept frequency light source and the sample arm and the reference arm. In the first optical fiber coupler, the light source is divided into two beams, 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 the reference arm.
The swept-frequency optical coherence tomography imaging system according to claim 2, wherein the attitude adjustment unit is drivingly connected to the DSV-OCT system; the attitude adjustment unit includes an X-axis position platform and a Y-axis displacement platform , One or more of the Z-axis displacement platforms.
A dual-field optical coherence tomography imaging system according to claim 3, characterized in that:

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;

Correction introduction devices arranged opposite to both sides of the sample to be tested, the correction introduction device comprising a collimator 1 and a focusing lens;

The two sampling light sources are introduced into the collimator 1 in the device through the calibration on both sides of the sample to be tested, and after passing through the focusing lens, the sampling light sources are provided to both sides of the sample to be tested for double-sided Imaging.
A dual-field optical coherence tomography imaging system according to claim 4, wherein one end of the reference arm corresponds to the optical fiber coupler, and the other end of the reference arm introduces a reference light source, The other end of the reference arm corresponds to the return device, and the reference light source inputs the reference light source into the balanced photodetector after passing through the return device.
A dual-field optical coherence tomography imaging system according to claim 5, characterized in that: the return device comprises a collimator and a flat mirror which are arranged oppositely; the reference light source is introduced into the return After the device passes through a set of two collimators and a flat mirror, the reference light source is introduced into the balanced photodetector by an opposite set of flat mirrors and a second collimator.
A method for detecting the thickness of non-transparent materials using a dual-field optical coherence tomography imaging system according to any one of claims 1 to 6, characterized in that:

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 A-scan or/and 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 collect the returned data through the PC. Processing; A scan: point measurement on the sample; B scan: realize a one-dimensional linear scan of the light spot on the sample surface to obtain a cross-sectional view of the scanning position; C scan: realize a two-dimensional area scan of the light spot on the sample surface to obtain The three-dimensional structure diagram of the scanning position;

Step 4: The PC converts the processed data and calculates the thickness of the sample.
The method for detecting the thickness of a non-transparent material of a swept optical coherence tomography imaging system according to claim 5, wherein: in step 2, the sample arm creates the output sampling light source into two sampling light sources Then, after the two sampling light sources are introduced symmetrically to the opposite sides of the sample to be tested, the reference light source returned from the reference arm is three-coupled through the fiber coupler, and then input to the balanced photodetector to cause interference The interference signal is generated, and then the interference signal is transmitted back to the PC.
The method for detecting the thickness of non-transparent materials of a swept optical coherence tomography imaging system according to claim 7, characterized in that: in step three, the thickness measurement is performed by the DSV-OCT system, and the DSV-OCT system is passed through the opaque The surface profile of the material is measured for thickness, 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:

d=[(z bf -z rs )+(z af -z ls )]×px; formula (2)

Among them, px represents the pixel size in the axial direction.
A method for detecting the thickness of non-transparent materials in a swept optical coherence tomography imaging system according to claim 9, characterized in that:

Place the material with thickness d between the two focusing lenses. At this time, there are two ways to place the sample;

Method one, 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:

d=[(z bf -z rs )+(z af -z ls )]×px; formula (2)

Among them, 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:

d=[(z bf -z rs )-(z ls -z af )]×px; formula (3)

Formulas (2) and (3) can be restated in the same form