A method to improve OCT imaging accuracy

Abstract

A method for improving OCT imaging accuracy. The present invention relates to the field of processing detection technology, and specifically to the field of a method for improving OCT imaging accuracy. The present invention introduces an electrically controlled crystal in the propagation direction of a reference beam, and controls the electrically controlled crystal by applying an external electric field to change its refractive index, thereby changing the light intensity of the reference beam, making its light intensity equal to the light intensity of a test beam reflected from the surface of the inspected material, thereby improving the OCT imaging accuracy. The method for improving OCT imaging accuracy comprises: a reference beam and a test beam; an electrically controlled crystal is provided in the propagation direction of the reference beam; the electrically controlled crystal is used to adjust the light intensity of the reference beam to obtain a reference beam with adjusted light intensity; the test beam is reflected from the surface of the inspected material to obtain a returned test beam; when the light intensity of the reference beam with adjusted light intensity is equal to the light intensity of the returned test beam, the OCT imaging accuracy is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of processing detection, and in particular to the technical field of a method for improving OCT imaging accuracy. Background Art

[0002] Optical coherence tomography (OCT), a high-resolution, non-invasive optical imaging technology, has seen its application in the manufacturing field expand in recent years, demonstrating unique advantages in industrial inspection and manufacturing. In laser welding, OCT enables real-time monitoring of weld penetration, addressing the inefficiency of traditional destructive inspection. In composite materials, OCT can identify bubbles, cracks, and delamination. In the semiconductor industry, OCT can detect defects on wafer surfaces and within internal structures. Furthermore, OCT can be used to assess the thickness and uniformity of industrial coatings.

[0003] OCT is an optical coherence detection technology that uses the interference of a test beam reflected by a material and a reference beam to form an interference image to reflect the surface or internal information of the material. Therefore, the clarity of the interference image is a key factor in ensuring measurement accuracy. However, the current OCT technology mainly uses the following technical means to improve the clarity of the interference image:

[0004] (1) Time-domain OCT (TD-OCT) technology: By driving the reference mirror to perform linear displacement through piezoelectric ceramics and precisely adjusting the optical path of the reference arm, depth-direction tomographic imaging is achieved. This method can intuitively obtain depth information, but it has obvious defects in practical applications. Due to the speed limit of mechanical components, the imaging rate of TD-OCT is low, with a typical value below 2kHz A-line. In addition, the high vibration sensitivity of mechanical movement leads to a decrease in signal-to-noise ratio, and the depth sensitivity decays exponentially with the detection distance. These defects limit the application of TD-OCT in material detection, especially in scenarios requiring fast imaging and high sensitivity.

[0005] (2) Frequency Domain OCT (FD-OCT) technology: It completely revolutionizes signal processing through spectral domain sampling and is divided into spectral OCT (SD-OCT) and swept spectrum OCT (SS-OCT). SD-OCT uses a low-coherence broadband light source, which is then split by a diffraction grating and synchronously collected by a linear array detector, significantly improving imaging speed and sensitivity. However, SS-OCT requires an expensive high-speed wavelength tunable light source and has disadvantages in phase stability. Although SD-OCT is considered an ideal choice in the field of industrial inspection, it has high requirements for light sources and detectors, and its cost is relatively high.

[0006] (3) All-fiber probe technology: GRIN fiber or fiber lens is used as the focusing element, which simplifies the preparation process. By adding a phase mask or shaping the output beam into a Bessel beam, the focal depth can be effectively extended. However, this technology also has drawbacks: spherical fiber lens and GRIN fiber lens will produce aberrations due to their own parabolic refractive index distribution, which reduces the imaging resolution.

[0007] Although the above technical means improve the clarity of the interference image, there are still technical problems such as reduced signal-to-noise ratio due to the movement limitations of mechanical components, phase instability and high cost, and aberrations caused by the refractive index distribution of the elements themselves, which reduces the imaging resolution. Summary of the Invention

[0008] To address the technical challenges of existing techniques for improving interference image clarity, such as reduced signal-to-noise ratio, phase instability, and high cost due to mechanical component movement limitations, as well as reduced imaging resolution caused by aberrations due to the refractive index distribution of the components, this paper proposes a method for improving OCT imaging accuracy. This method introduces an electrically controlled crystal in the direction of propagation of the reference beam. By applying an external electric field to control the crystal's refractive index, the crystal changes its intensity, thereby altering the reference beam's intensity to equal that of the test beam reflected from the surface of the material being inspected, thereby improving OCT imaging accuracy.

[0009] The method comprises the following steps:

[0010] Methods for improving OCT imaging accuracy include: reference beam and test beam;

[0011] An electrically controlled crystal is provided in the propagation direction of the reference beam;

[0012] The electrically controlled crystal is used to adjust the intensity of the reference beam to obtain a reference beam with adjusted intensity;

[0013] The test beam is reflected by the surface of the material being tested to obtain a returned test beam;

[0014] When the intensity of the reference beam for adjusting the light intensity is equal to the intensity of the returned test beam, the OCT imaging accuracy is improved.

[0015] Furthermore, the electrically controlled crystal is a device whose refractive index can be changed under the action of an external electric field.

[0016] Furthermore, by changing the refractive index of the electrically controlled crystal, the transmittance of the electrically controlled crystal can be adjusted.

[0017] Furthermore, the transmittance of the electrically controlled crystal is positively correlated with the intensity of the reference light beam passing through the electrically controlled crystal.

[0018] Furthermore, the method for improving OCT imaging accuracy further comprises: an automatic control module;

[0019] The automatic control module can provide an external electric field for the electrically controlled crystal.

[0020] Furthermore, the automatic control module receives the returned test light beam and calculates the external electric field value required for the electrically controlled crystal according to its light intensity.

[0021] Furthermore, the method for improving OCT imaging accuracy is applied to an OCT imaging device.

[0022] Furthermore, the OCT imaging device includes: a broadband light source, a fiber coupler, a reference optical path, a test optical path and an imaging processing unit;

[0023] A broadband light source emits a near-infrared beam to a fiber coupler, which splits the near-infrared beam into a reference beam and a test beam. After passing through the reference optical path and the test optical path respectively, the reference beam and the test beam interfere at the fiber coupler to form a coherent beam. The imaging processing unit receives and processes the coherent beam to obtain OCT imaging with improved imaging accuracy.

[0024] Furthermore, the reference optical path is used to receive a reference beam and output a reference beam with adjusted light intensity;

[0025] The test light path is used to receive a test light beam and output a returned test light beam.

[0026] The beneficial effects of the method of the present invention are:

[0027] (1) The method described in the present invention sets an electrically controlled crystal in the propagation direction of the reference beam. When detecting different materials, the electrically controlled crystal is controlled by applying an external electric field to change its refractive index, thereby adjusting its reflection coefficient and transmission coefficient. Finally, the intensity of the reference beam is adjusted to make its intensity equal to the intensity of the test beam reflected by the surface of the material being detected, thereby improving the OCT imaging accuracy.

[0028] (2) The control method adopted by the method of the present invention is simpler and more efficient than the existing method for improving the clarity of interference images. Since it is not affected by the movement of mechanical parts, the signal-to-noise ratio and phase are more stable. Since the method of the present invention can adjust the refractive index of the electrically controlled crystal, the method of the present invention will not produce aberrations due to the refractive index distribution of the component itself, and can ensure higher imaging resolution by adjusting the refractive index.

[0029] (3) The method described in the present invention also has an automatic control module, which controls the electrically controlled crystal through the automatic control principle, thereby realizing fully automatic intelligent control. It can automatically provide an external electric field for the electrically controlled crystal according to the intensity of the returned test beam so as to adjust the intensity of the reference beam. Due to its fully automatic intelligent control, it can also save labor costs, reduce manual calculation errors, and improve OCT imaging efficiency.

[0030] (4) The OCT imaging device of the present invention provides a reasonable optical path layout for the method of the present invention, saving space so as to subsequently improve the OCT imaging accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a structural diagram of the OCT imaging device of the present invention;

[0032] 1- broadband light source, 2- fiber coupler, 201- fiber coupler light outlet A, 202- fiber coupler light outlet A, 301- electrically controlled crystal, 302- reference focusing lens, 303 plane reflector, 401- test folding mirror A, 402- test folding mirror B, 403- scanning galvanometer, 5- imaging processing unit, 501- collimator, 502- grating, 503- imaging focusing lens, 504- linear array CCD, 6- spectrometer, 7- focusing lens, 801- sensor, 802- controller, 803 driving circuit and 9- surface of inspected material. DETAILED DESCRIPTION

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0034] Example 1

[0035] This embodiment provides a method for improving OCT imaging accuracy.

[0036] OCT is an optical coherence measurement technology that uses interference between a test beam reflected by a material and a reference beam to form an interference image, revealing information about the material's surface or interior. Therefore, the clarity of this interference image is crucial for ensuring measurement accuracy. The present invention's technical solution does not focus on the industry's conventional approach of improving interference image clarity by considering the light source, reference arm optical path, and focus. Instead, it seeks a solution based on fundamental principles by analyzing the interference image clarity formula.

[0037] The clarity of the interference image is given by formula (1):

[0038] (1)

[0039] in, Indicates the visibility (clarity) of interference fringes, that is, the quantity that characterizes the clarity of fringes. represents the maximum light intensity in the interference region, Indicates the minimum light intensity in the interference area. The light intensity of any point P in the interference area is equal to the light intensity of the two lights participating in the interference (the reference beam for adjusting the light intensity and the returned test beam). and The relationship is shown in formula (2), where express and Phase difference:

[0040] (2)

[0041] Obviously, according to formula (2), the maximum light intensity in the interference area is:

[0042] (3)

[0043] The minimum light intensity in the interference area is:

[0044] (4)

[0045] Will and Substituting into formula (1), we can get and and Relationship:

[0046] (5)

[0047] It can be seen from formula (5) that the clarity of the interference image depends largely on the intensities of the two coherent lights. Specifically, the closer the intensities of the two coherent lights are, the clearer the image is, and vice versa. According to formula (5), the clarity of the interference image is best when the intensities of the two coherent lights are exactly equal. Therefore, in OCT, making the intensity values ​​of the test beam and the reference beam equal is the most ideal situation.

[0048] Relationship between refractive index and light intensity: The intensity of a light beam depends on the reflectivity and transmittance when the light beam passes through the surface of each component, and the reflectivity and transmittance depend on the reflection coefficient and transmission coefficient, which are given by the Fresnel formula: (6)

[0049] (7)

[0050] in, and They represent the reflection coefficient and transmission coefficient of the s-wave, respectively. The s-wave represents the component of the light beam in the s direction. and Represent the refractive index on both sides of the element surface, and They represent the incident angle and refraction angle of the light beam on the surface of the element respectively.

[0051] According to formulas (6) and (7), it can be seen that the magnitude of the reflection coefficient and the transmission coefficient are both related to the refractive index of the element, that is, changes in the refractive index of the element will cause changes in the reflection coefficient and the transmission coefficient, thereby causing changes in the reflectivity and transmittance, and ultimately causing changes in the intensity of the light beam passing through the element. Therefore, in this embodiment, as long as the refractive index of any element in the propagation direction of the reference beam can be controlled to change, the intensity of the reference beam can be controlled. However, the refractive index is determined by the density of the atomic / molecular arrangement and the electronic polarizability within the material. The atomic structure of conventional solid-state elements (such as convex lenses and plane mirrors) is difficult to dynamically change at a macroscopic scale. For example, the refractive index of traditional optical elements is solidified by the composition during production (such as the addition of rare earth elements) and cannot be directly adjusted after the device is manufactured.

[0052] Therefore, if Figure 1 As shown, the method of the present invention adds an electrically controlled crystal 301 in the propagation direction of the reference beam. The electrically controlled crystal 301 selected in this embodiment is a device that uses the electro-optical effect to change the refractive index of the electrically controlled crystal 301 under the action of an external electric field.

[0053] Relationship between electric field and refractive index: Since the refractive index of the electrically controlled crystal 301 is anisotropic, it is expressed as a tensor, which is the change induced by the electric field. That is, when the electric field acting on the crystal changes, the tensor will change, that is, the refractive index will change. The specific expression is not unique and depends on the type of electro-optical effect.

[0054] Once the type of crystal electro-optical effect is determined, the correspondence between the electric field and the refractive index in the expression is uniquely determined, and the refractive index of the electrically controlled crystal 301 can be controlled by applying an external electric field, that is, the required external electric field value can also be calculated by the refractive index.

[0055] The method of the present invention changes the refractive index of the electrically controlled crystal 301 by applying an external electric field, thereby adjusting the transmittance of the electrically controlled crystal 301 .

[0056] The transmittance of the electrically controlled crystal 301 is positively correlated with the intensity of the reference beam passing through the electrically controlled crystal 301 . Therefore, the electrically controlled crystal 301 adjusts the intensity of the reference beam through the action of an external electric field, thereby obtaining a reference beam with adjusted intensity.

[0057] The test beam is reflected by the surface 9 of the material to be tested to obtain a returned test beam;

[0058] When the intensity of the reference beam for adjusting the light intensity is equal to the intensity of the returned test beam, the OCT imaging accuracy is improved.

[0059] Example 2

[0060] This embodiment is a further limitation of embodiment 1. The method for improving OCT imaging accuracy in this embodiment further comprises: an automatic control module;

[0061] The automatic control module can provide an external electric field for the electrically controlled crystal.

[0062] like Figure 1 As shown, the automatic control module includes: a sensor 801, a controller 802 and a drive circuit 803;

[0063] The sensor 801 receives the returned test beam (optical signal) and converts the optical signal into an electrical signal, which is then transmitted to the controller 802. The controller 802 processes the received electrical signal to obtain the intensity of the returned test beam.

[0064] The controller 802 calculates the required refractive index and external electric field value of the electrically controlled crystal 301 based on the relationship between the electric field and the refractive index and the relationship between the refractive index and the light intensity described in Example 1.

[0065] The driving circuit 803 generates a high-precision voltage based on the calculation result of the controller 802, thereby controlling the refractive index of the electrically controlled crystal 301 to change.

[0066] Example 3

[0067] This embodiment further limits Embodiments 1 and 2.

[0068] The method for improving the OCT imaging accuracy described in Examples 1 and 2 is applied to an OCT imaging device.

[0069] like Figure 1 As shown, the OCT imaging device includes: a broadband light source 1, a fiber coupler 2, a reference optical path, a test optical path and an imaging processing unit 5;

[0070] The broadband light source 1 emits a near-infrared beam to the optical fiber coupler 2, and the optical fiber coupler 2 splits the near-infrared beam into a reference beam and a test beam;

[0071] After passing through the reference optical path and the test optical path respectively, the reference beam and the test beam interfere at the optical fiber coupler 2 to form a coherent beam;

[0072] The reference optical path is used to receive a reference beam and output a reference beam with adjusted light intensity;

[0073] In the reference optical path, the reference beam passes through the optical fiber coupler light outlet A201, the electrically controlled crystal 301, and the reference focusing lens 302 in sequence before being incident on the plane mirror 303. After being reflected by the plane mirror 303, the reference beam passes through the reference focusing lens 302, the electrically controlled crystal 301, and the optical fiber coupler light outlet A201 in sequence before being incident on the optical fiber coupler 2.

[0074] In the reference optical path, the electrically controlled crystal 301 can adjust the intensity of the reference beam, so the beam output by the reference optical path is a reference beam with adjusted intensity.

[0075] The optical fiber coupler light outlet A201, the electrically controlled crystal 301, the reference focusing lens 302 and the plane reflector 303 constitute a reference arm.

[0076] The test light path is used to receive a test light beam and output a returned test light beam.

[0077] In the test optical path, the test beam passes through the optical fiber coupler light outlet B202, the test folding mirror A401, the test folding mirror B402, the scanning galvanometer 403, the beam splitter 6 and the focusing lens 7 in sequence before being incident on the surface 9 of the material to be tested. The surface 9 of the material to be tested receives the test beam and reflects the test beam to obtain a returned test beam.

[0078] The focusing lens 7 is used to converge the test light beam onto the surface 9 of the material to be inspected. The composition of the focusing lens 7 can be configured by those skilled in the art according to actual conditions.

[0079] The returned test light beam passes through the focusing lens 7 and enters the spectrometer 6. The spectrometer 6 divides the returned test light beam into two beams. One beam enters the automatic control module to generate an external electric field; the other beam passes through the scanning galvanometer 403, the test folding mirror B402, the test folding mirror A401 and the optical fiber coupler light outlet B202 in sequence and then enters the optical fiber coupler 2.

[0080] The imaging processing unit 5 includes a collimator 501 , a grating 502 , an imaging focusing lens 503 and a linear array CCD 504 .

[0081] After the coherent light beam enters the imaging processing unit 5, it passes through the collimator 501, grating 502 and imaging focusing lens 503 in sequence before entering the linear array CCD 504 to obtain an interference image. The interference image is subjected to the Fourier transform algorithm to extract the phase distribution, and then the phase distribution information is converted into a clear image of the inspected surface (OCT imaging to improve imaging accuracy).

[0082] Example 4

[0083] This embodiment further limits Embodiments 1 to 3.

[0084] The method of the present invention can also perform electroplating, ultrasonic, laser and other processing on the surface while detecting as needed.

Claims

1. A method for improving OCT imaging accuracy, characterized in that: Methods for improving OCT imaging accuracy include: reference beam and test beam; An electrically controlled crystal is provided in the propagation direction of the reference beam; The electrically controlled crystal is used to adjust the intensity of the reference beam to obtain a reference beam with adjusted intensity; The test beam is reflected by the surface of the material being tested to obtain a returned test beam; When the intensity of the reference beam for adjusting the light intensity is equal to the intensity of the returned test beam, the OCT imaging accuracy is improved.

2. A method for improving OCT imaging accuracy according to claim 1, characterized in that: The electrically controlled crystal is a device whose refractive index can be changed under the action of an external electric field.

3. The method for improving OCT imaging accuracy according to claim 2, characterized in that: By changing the refractive index of the electrically controlled crystal, the transmittance of the electrically controlled crystal can be adjusted.

4. The method for improving OCT imaging accuracy according to claim 3, characterized in that: The transmittance of the electrically controlled crystal is positively correlated with the intensity of the reference light beam passing through the electrically controlled crystal.

5. The method for improving OCT imaging accuracy according to claim 4, characterized in that: The method for improving OCT imaging accuracy further comprises: an automatic control module; The automatic control module can provide an external electric field for the electrically controlled crystal.

6. The method for improving OCT imaging accuracy according to claim 5, characterized in that: The automatic control module receives the returned test light beam and calculates the external electric field value required for the electrically controlled crystal according to its light intensity.

7. The method for improving OCT imaging accuracy according to claim 6, characterized in that: The method for improving OCT imaging accuracy is applied to an OCT imaging device.

8. The method for improving OCT imaging accuracy according to claim 7, characterized in that: The OCT imaging device comprises: a broadband light source (1), a fiber coupler (2), a reference light path, a test light path, and an imaging processing unit (5); A broadband light source (1) emits a near-infrared beam to a fiber coupler (2). The fiber coupler (2) divides the near-infrared beam into a reference beam and a test beam. After the reference beam and the test beam pass through a reference optical path and a test optical path respectively, they interfere at the fiber coupler (2) to form a coherent beam. An imaging processing unit (5) receives and processes the coherent beam to obtain an OCT imaging with improved imaging accuracy.

9. The method for improving OCT imaging accuracy according to claim 8, characterized in that: The reference optical path is used to receive a reference beam and output a reference beam with adjusted light intensity; The test light path is used to receive a test light beam and output a returned test light beam.

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