Optical coherence tomography system using single-frequency laser and application thereof

Abstract

The invention provides an optical coherence tomography system using single-frequency laser and application of the optical coherence tomography system. The system is mainly composed of a single-frequency laser, a polarization beam splitter, a lens, a reflector, an optical mixer, a detector, data processing equipment and the like. One part of laser emitted by the single-frequency laser serves as local oscillation light, the other part of the laser is divided into horizontal polarized light and vertical polarized light through the polarization beam splitter, the horizontal polarized light and the vertical polarized light are modulated through a series of lenses and reflectors and then combined to irradiate a target area, scattered echoes and the local oscillation light are combined and mixed, and after being detected and converted, the scattered echoes are collected through the data collection module and transmitted to the computer to be processed. According to the system, time domain frequency sweeping of the frequency sweeping OCT is converted into space domain scanning, a common single-frequency laser is adopted to replace a frequency sweeping laser, and the cost is effectively reduced. Compared with the similar technology, the system has many advantages. The method has wide application prospects in the fields of medicine, industry, material science and the like.

Description

Technical Field

[0001] The invention relates to the field of laser technology, in particular to an optical coherence tomography system using single-frequency laser and application thereof. Background Art

[0002] Optical Coherence Tomography (OCT) is a non-invasive optical imaging technology that has shown extremely broad application prospects in many fields such as medicine, industry and materials science since its introduction in the early 1990s. This technology can obtain cross-sectional images of biological tissues at micron-level resolution, providing key microscopic information for research and detection in various fields.

[0003] Based on the differences in imaging principles and system design, OCT is mainly divided into time domain OCT and frequency domain OCT, among which frequency domain OCT is further subdivided into spectral domain OCT and swept frequency OCT. Their basic optical paths are all based on the Michelson interference optical path, and the measurement results are the interference signals of the reference optical path and the signal optical path.

[0004] Spectral domain OCT uses a superluminescent diode (SLD) as a light source, which is required to have a continuous spectrum with a width of tens of nm or even hundreds of nm. However, since SLD is a wide-spectrum light source, its coherence length is low and the quantum fluctuation noise is high. This greatly affects the signal-to-noise ratio of the image during the imaging process of spectral domain OCT, reduces the quality and accuracy of the image, and limits the application of this technology in scenarios with high requirements for imaging quality.

[0005] Sweep-frequency OCT uses a continuously tunable light source, each of which is a narrowband light source, and therefore has a good coherence length. However, this light source places extremely high demands on linear frequency sweeping, and usually requires good linear frequency tuning within a spectral range of tens of nm or even hundreds of nm in width. To meet this requirement, the design and implementation of the system becomes extremely complex, and it is difficult to balance the scanning speed. Real-time performance has become the biggest problem facing swept-frequency OCT, and it cannot meet some application scenarios that have high requirements for detection speed, such as dynamic biological tissue detection, rapid industrial detection, etc.

[0006] In summary, the existing spectral domain OCT and swept frequency OCT have their own defects in terms of light source characteristics and system performance, which limits the further development and wide application of OCT technology. The optical coherence tomography system using a single-frequency laser of the present invention aims to effectively solve the problems of high cost and difficulty in balancing scanning speed and resolution in the existing technology by converting the time domain frequency sweep of swept frequency OCT into spatial domain scanning and using an ordinary single-frequency laser instead of a swept frequency laser, thereby improving the comprehensive performance of the OCT system. Summary of the invention

[0007] The embodiments of the present invention provide an optical coherence tomography system using a single-frequency laser and its application, in order to solve the problems that the superluminescent diode light source used in the spectral domain OCT in the current technology has a low coherence length and high quantum fluctuation noise, and the continuously tunable light source of the swept frequency OCT has high requirements for linear frequency sweeping and it is difficult to balance the scanning speed. Both have defects that affect the application and development of optical coherence tomography technology.

[0008] The core technology of the present invention is mainly to convert the time domain scanning of the swept-frequency OCT into spatial domain scanning, replace the swept-frequency laser with an ordinary single-frequency laser, while reducing the cost and taking into account the scanning speed, resolution and other parameters, and to innovate and optimize the optical path structure, phase scanning and data processing to improve the overall performance of the system.

[0009] In a first aspect, the present invention provides an optical coherence tomography system using a single-frequency laser, comprising: Single-frequency laser, used for emitting single-frequency laser; A first polarization beam splitter, used for splitting a portion of the laser beam emitted by the single-frequency laser into horizontally polarized light and vertically polarized light; A first lens and a first reflector, wherein the horizontally polarized light is reflected by the first lens and the first reflector in sequence; A second reflector, a second lens, and a third lens. The vertically polarized light is reflected by the second reflector and then enters the second lens and the third lens. A second polarization beam splitter, used for combining the modulated horizontally polarized light and the vertically polarized light; The first objective lens irradiates the combined light onto the target area; A second objective lens receives scattered echoes from the target area; An optical mixer mixes the scattered object light with the local oscillator light separated by the single-frequency laser; A balanced detector detects the mixed light and realizes photoelectric conversion; An analog-to-digital converter converts the analog signal output by the balanced detector into a digital signal; Data acquisition module, collecting digital signals; The computing unit stores and processes the collected raw data.

[0010] Furthermore, the first lens and the second lens perform co-directional scanning along the y direction, and when the first lens moves along the negative y direction, the second lens moves along the positive y direction.

[0011] Furthermore, the data processing method of the computing unit includes: Perform FFT transformation on each layer of collected data to transform the time domain variables into the frequency domain; Perform matched filtering on the FFT transformed data.

[0012] Furthermore, during the detection process, the target area moves along the y direction, and when the movement reaches a spot diameter of the target area, an imaging detection is completed.

[0013] Furthermore, after completing the detection of a certain layer of the target area, the target area is stepped along the z direction to repeat the detection, thereby achieving three-dimensional tomographic imaging of the target area.

[0014] Furthermore, the resolution of the system in the z direction is controlled by a nano-translation stage.

[0015] Furthermore, the computing unit is a computer.

[0016] In a second aspect, the present invention provides an optical coherence tomography system device using a single-frequency laser for application in the field of medical detection.

[0017] In a third aspect, the present invention provides an optical coherence tomography system device using a single-frequency laser for application in the field of industrial detection.

[0018] In a fourth aspect, the present invention provides an optical coherence tomography system device using a single-frequency laser for application in the field of material science research.

[0019] The main contributions and innovations of the present invention are as follows: 1. Reduce costs: Use ordinary single-frequency lasers instead of swept-frequency lasers. Sweep-frequency lasers are expensive and have high requirements for linear sweeping, while single-frequency lasers are low-cost, which greatly reduces costs while ensuring system functions, making the equipment more cost-effective.

[0020] 2. Improve energy coupling efficiency and vibration resistance: Use spatial optical paths instead of optical fiber paths. Spatial optical paths improve the system's energy coupling efficiency and greatly reduce the impact of external vibrations on the system. This not only enhances the stability of the system, but also facilitates portable scanning by mobile devices, allowing the system to be used in more scenarios, such as on-site detection, mobile medical care, etc.

[0021] 3. Improve data quality and imaging stability: Using single-frequency lasers has better coherence than low-coherence light sources in existing technologies, and can obtain data with a high signal-to-noise ratio. Phase scanning is achieved through lens movement, which can ensure the generation of stable linear phase terms, thereby ensuring the resolution of the system and the consistency of system measurement, and improving imaging quality.

[0022] 4. Convenient for subsequent algorithm processing: Phase scanning uses a high-speed motor for reciprocating motion, which can provide a high-linearity linear phase term while ensuring the scanning speed. Compared with the existing technology that uses an optoelectronic modulator and requires a complex RF circuit for the drive circuit and is difficult to ensure the linearity of the modulation, the design of the present invention is more convenient for subsequent algorithm processing and reduces the complexity of system design and operation.

[0023] The details of one or more embodiments of the invention are set forth in the following drawings and description so that other features, objects, and advantages of the invention are more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings: Figure 1 4 is a framework diagram of an optical coherence tomography system using a single-frequency laser according to an embodiment of the present invention.

[0025] In the figure, 1. single-frequency laser; 2. first polarization beam splitter; 3. first lens; 4. first reflector; 5. second reflector; 6. second lens; 7. third lens; 8. second polarization beam splitter; 9. first objective lens; 10. target area; 11. second objective lens; 12. optical mixer; 13. balanced detector; 14. analog-to-digital converter; 15. data acquisition module; 16. computing unit. DETAILED DESCRIPTION

[0026] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with one or more embodiments of this specification. Instead, they are merely examples of devices and methods consistent with some aspects of one or more embodiments of this specification as detailed in the appended claims.

[0027] It should be noted that: in other embodiments, the steps of the corresponding method are not necessarily performed in the order shown and described in this specification. In some other embodiments, the steps included in the method may be more or less than those described in this specification. In addition, a single step described in this specification may be decomposed into multiple steps for description in other embodiments; and multiple steps described in this specification may be combined into a single step for description in other embodiments.

[0028] Embodiment 1 The present invention aims to provide an optical coherence tomography system using a single-frequency laser. Figure 1 The system includes: a single-frequency laser 1, a first polarization beam splitter 2, a first lens 3, a first reflector 4, a second reflector 5, a second lens 6, a third lens 7, a second polarization beam splitter 8, a first objective lens 9, a target area 10, a second objective lens 11, an optical mixer 12, a balanced detector 13, an analog-to-digital converter 14, a data acquisition module 15, and a computing unit 16.

[0029] In this embodiment, a single-frequency laser 1 emits a beam of single-frequency laser light, a part of the light enters the optical mixer 12 as the local oscillator light, and a part of the light passes through the first polarization beam splitter 2 to split the light beam into horizontal polarized light and vertical polarized light. The horizontal polarized light is incident on the first lens 3 and then on the first reflector 4, and the vertical polarized light is incident on the second reflector 5 and reflects into the second lens 6 and the third lens 7. The modulated horizontal polarized light and the vertical polarized light are combined in the second polarization beam splitter 8 and irradiated to the target area 10 through the first objective lens 9. The laser irradiates the target surface or a certain depth inside. The scattered echo is received by the second objective lens 11 and enters the receiving optical path. The scattered object light and the local oscillator light are mixed in the optical mixer 12 and then detected by the balanced detector 13 to realize photoelectric conversion, converted into digital signals by the analog-to-digital converter 14, and data acquisition is performed by the data acquisition module 15. The raw data is stored and processed by the calculation unit 16.

[0030] Among them, the optical mixer 12 is an optical device that mixes two beams of light. In this system, it receives the scattered object light and the local oscillator light separated by the single-frequency laser, and mixes the two beams of light. Through mixing, the light fields of the two beams of light interact with each other to generate a mixed light signal containing information about the target area. Its principle is based on the interference phenomenon of light. By using the interference of the local oscillator light and the object light, the weak information of the target area carried in the object light is amplified and modulated, making it easier to detect and analyze this information later. For example, when detecting biological tissues or industrial materials, the object light carries information such as the structure and composition of the target area. By mixing with the local oscillator light in the optical mixer, this information is converted into light signal intensity or phase changes that are easier to detect.

[0031] The balanced detector 13 is a device for realizing photoelectric conversion. It receives the optical signal after mixing from the optical mixer and converts the optical signal into an electrical signal. The balanced detector 13 adopts a differential detection method, which can effectively suppress common-mode noise and improve the sensitivity and signal-to-noise ratio of detection. In this system, when the mixed optical signal output by the optical mixer is irradiated onto the balanced detector, the photosensitive element in the detector converts the optical energy into a current or voltage signal. Due to the use of a balanced detection structure, it has a strong ability to suppress common-mode interference such as stray light and background noise in the environment, and can accurately convert the useful information in the mixed optical signal into an electrical signal output.

[0032] Further, the mathematical principle of this system is described as follows: The first lens 3 and the second lens 6 perform the same direction scanning along the y direction, that is, when the first lens 3 moves along the negative y direction, the second lens 6 moves along the positive y direction to realize the scanning of the emission light field. The emission light field can be expressed by the mathematical formula as follows:

[0033] in is the horizontally polarized light field in the emitted light field, is the vertically polarized light field in the emitted light field, represents the unit vector in the y direction, represents the unit vector in the x direction, represents the intensity of the emitted light field, represents the scanning period of the first lens 3 and the second lens 6, is a time variable, indicating that the light field changes with time, represents the size of the emitted light field along the x direction, represents the size of the emitted light field along the y direction, x,y represents the coordinate variables of the light field, represents the wavelength of single-frequency laser 1, represents the focal length of the first lens 3 and the second lens 6, represents the scanning speed of the first lens 3 and the second lens 6, represents the initial position offset of the first lens 3 and the second lens 6, is the focal length of the third lens 7.

[0034] The emission light field is irradiated to the target area 10 through the objective lens. The magnification of the first objective lens 9 is M times. The photocurrent equation after mixing by the optical mixer 12 and then detected by the balanced detector 13 is:

[0035] represents the output photocurrent of the balanced detector, n represents the number of sampling times along the y direction, during the detection process, the target area 10 moves along the y direction, and when the movement reaches the spot diameter of the target area 10, an imaging detection is completed. n represents the nth step of this process, C represents the constant coefficient, M is the magnification of the first objective lens 9, represents the step interval of each movement of the target area 10 along the y direction, , Represents the coordinate point of the target, , is the time variable, represents the size of the emitted light field along the x direction, represents the size of the emitted light field along the y direction, express:

[0036] in , , represents the wavelength of single-frequency laser 1, represents the focal length of the first lens 3 and the second lens 6, represents the scanning speed of the first lens 3 and the second lens 6, represents the initial position offset of the first lens 3 and the second lens 6, is the focal length of the third lens 7.

[0037] After completing the detection of each layer as described above, the target area 10 is stepped along the z direction. , and then repeat the imaging process of each layer mentioned above to achieve three-dimensional tomographic detection of the target.

[0038] Preferably, the data processing of each layer is as follows: First step, FFT:

[0039] represents the Fourier transform, which transforms the time domain variable Transform to frequency domain , D is the coefficient. FFT is the Fast Fourier Transform, which is a key step in processing each layer of collected data. When analyzing the scattered echo signal of the target area, FFT can decompose the signal into different frequency components, laying the foundation for further removing noise and extracting useful information, thereby improving the imaging quality and system resolution, and helping to image and analyze the target area more accurately.

[0040] The second step is matched filtering. The matched filter is:

[0041] in, represents the wavelength of single-frequency laser 1, , y represents the target surface coordinate.

[0042]

[0043] in, The part represents the process of convolution of the sinc function with the delta function, and D represents a constant. represents the scanning period of the first lens 3 and the second lens 6, M is the magnification of the first objective lens 9, represents the size of the emitted light field along the x direction, , , is the time domain variable above The frequency domain variable after FFT transformation.

[0044] The resolution in the x and y directions is:

[0045] M is the magnification of the first objective lens 9, represents the focal length of the first lens 3 and the second lens 6, represents the scanning speed of the first lens 3 and the second lens 6, is the focal length of the third lens 7, represents the size of the emitted light field along the y direction, It represents the scanning period of the first lens 3 and the second lens 6.

[0046] Among them, matched filtering is a key step after FFT transformation in the data processing flow of the optical coherence tomography system of the present invention, and plays an important role in improving signal quality and imaging resolution.

[0047] Definition and Principle: Matched filtering is a signal processing technique whose basic principle is to design a filter so that its characteristics match those of the signal to be detected. In the present invention, the design of the matched filter is adapted to the signal collected by the system, with the purpose of enhancing the target signal, suppressing noise and interference signals, and thus improving the signal-to-noise ratio of the signal. The filter processes the signal after FFT transformation in the frequency domain or time domain, and highlights the characteristics of the target signal through correlation calculation with the signal.

[0048] Role in the system: In the system of the present invention, matched filtering is crucial to improving imaging quality and resolution. After the laser irradiates the target area, the scattered echo signal contains the information of the target, but it is also mixed with various noises. The data transformed into the frequency domain by FFT can be further removed by matched filtering to make the target signal more prominent. By optimizing the parameters of the matched filter, it is possible to better adapt to the characteristics of the system and different detection requirements, enhance or suppress signals of specific frequencies, thereby improving the resolution of the system in the x and y directions, and helping the system to image and analyze the target area more accurately.

[0049] An example calculation: The wavelength is 405nm, the objective lens is 10 times, the focal length of the lens is 50mm, the scanning speed of the first lens 3 and the second lens 6 is 10mm / s, the width of the emission light field is 10mm, and the scanning period of the first lens 3 and the second lens 6 is 0.8s. The resolution in the x and y directions is 253nm and 202nm respectively. The resolution in the z direction is controlled by the nano-translation stage, and a tomographic accuracy of 10nm can be obtained.

[0050] Preferably, in addition to single-frequency lasers, new narrow-linewidth light sources can be used, such as distributed feedback lasers (DFBs), vertical-cavity surface-emitting lasers (VCSELs), etc. This type of light source has the characteristics of narrow linewidth and good coherence, and some products are low-cost and easy to integrate. Compared with single-frequency lasers, DFB lasers have higher wavelength stability and can improve the imaging accuracy of the system to a certain extent; VCSELs have the advantage of being easy to integrate into two-dimensional arrays. If applied to this system, faster array scanning imaging can be achieved.

[0051] Preferably, the FFT and matched filter algorithms of the present invention can be replaced by deep learning algorithms. Construct deep learning models such as convolutional neural networks (CNN) or recurrent neural networks (RNN) to process the collected raw data. Deep learning algorithms can automatically learn features and patterns in data without manually designing complex feature extraction and filtering algorithms. By training the model with a large amount of sample data, the system's robustness to noise and the imaging accuracy of complex targets can be improved. However, deep learning algorithms require a large amount of computing resources and training data, the training time of the model is long, and the interpretability of the model is relatively poor, so it can be selected according to actual needs.

[0052] Preferably, compressed sensing theory can also be applied for data processing. In the data acquisition stage, data is collected at a much lower sampling rate than the Nyquist rate, and then the compressed sensing algorithm is used to accurately reconstruct the original signal from a small amount of sampled data. This method can reduce the amount of data collected, reduce the pressure of data storage and transmission, and improve the real-time performance of the system. However, the compressed sensing algorithm has high requirements on the sparsity of the signal, and needs to be optimized and improved according to the signal characteristics of this system to ensure the effectiveness and accuracy of the algorithm. It can be selected according to actual needs.

[0053] Embodiment 2 Based on the same concept, the present invention also proposes an application of an optical coherence tomography system using a single-frequency laser in the field of medical detection, and the application includes: The optical coherence tomography system is used to obtain a cross-sectional image of biological tissue with a micron-level resolution. The laser is emitted by a single-frequency laser 1 in the system, and after being processed by a series of optical path components such as a first polarization beam splitter 2, the target area 10 of the biological tissue is illuminated to collect scattered echo signals. Using the data acquisition module 15 and the computer (computing unit 16) of the system to process and analyze the collected signals to detect the structure and pathological conditions of the biological tissue, wherein the data processing includes operations such as FFT transformation and matched filtering; Based on the system's three-dimensional tomography detection capabilities, it can perform imaging analysis on structures at different depths of biological tissues, assisting medical personnel in diagnosing diseases and formulating treatment plans.

[0054] Embodiment 3 Based on the same concept, the present invention also proposes an application of an optical coherence tomography system using a single-frequency laser in the field of industrial detection, and the application includes: The optical coherence tomography system is used to detect internal defects or surface quality of industrial products. The laser emitted by the system is transmitted through the optical path and illuminates the target area 10 of the industrial product to obtain reflected or scattered light signals. Through the system's data processing flow, the collected optical signal data is processed to identify defects such as cracks and cavities inside industrial products, or to detect quality parameters such as the flatness and roughness of the product surface; By utilizing the system's adjustable scanning parameters and resolution control functions, such as controlling the z-direction resolution through a nano-translation stage, the inspection accuracy requirements of different industrial products can be met, thus achieving quality control and defect analysis of industrial products.

[0055] Embodiment 4 Based on the same concept, the present invention also proposes an application of an optical coherence tomography system using a single-frequency laser in the field of material science research, the application comprising: The system is used to perform microstructure analysis on material samples. The laser emitted by the single-frequency laser 1 is processed by the optical path component and then irradiates the target area 10 of the material sample to collect scattered echo data. Through the data acquisition and processing functions of the system, the internal structure and component distribution of the material are studied. Data processing includes FFT operation to convert time domain data into frequency domain data and matched filtering operation; With the help of the system's three-dimensional tomography capability, the structure of material samples at different depths can be imaged and studied, and the structural evolution of materials during the preparation process or the relationship between material properties and microstructure can be analyzed, providing data support and analysis methods for material science research.

[0056] Those skilled in the art should understand that the technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0057] The above embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the attached claims.

Claims

1. An optical coherence tomography system using a single-frequency laser, characterized in that: include: A single-frequency laser (1), used for emitting single-frequency laser light; A first polarization beam splitter (2) for splitting a portion of the laser beam emitted by the single-frequency laser (1) into horizontally polarized light and vertically polarized light; a first lens (3) and a first reflector (4), wherein the horizontally polarized light is reflected by the first lens (3) and the first reflector (4) in sequence; a second reflector (5), a second lens (6), and a third lens (7), wherein the vertically polarized light is reflected by the second reflector (5) and then enters the second lens (6) and the third lens (7); A second polarization beam splitter (8), used for combining the modulated horizontally polarized light and the vertically polarized light; A first objective lens (9) irradiates the combined light beams onto a target area (10); A second objective lens (11) receives scattered echoes from the target area (10); An optical mixer (12) mixes the scattered object light with the local oscillator light separated by the single-frequency laser (1); A balanced detector (13) detects the mixed light to achieve photoelectric conversion; An analog-to-digital converter (14) converts the analog signal output by the balanced detector (13) into a digital signal; A data acquisition module (15) for collecting digital signals; The computing unit (16) stores and processes the collected raw data.

2. An optical coherence tomography system using a single-frequency laser as claimed in claim 1, characterized in that: The first lens (3) and the second lens (6) perform co-directional scanning along the y direction; when the first lens (3) moves along the negative y direction, the second lens (6) moves along the positive y direction.

3. The optical coherence tomography system using a single-frequency laser according to claim 1, characterized in that: The data processing method of the computing unit (16) comprises: Perform FFT transformation on each layer of collected data to transform the time domain variables into the frequency domain; Perform matched filtering on the FFT transformed data.

4. The optical coherence tomography system using a single-frequency laser according to claim 1, characterized in that: During the detection process, the target area (10) moves along the y direction, and when the movement reaches a light spot diameter of the target area (10), an imaging detection is completed.

5. An optical coherence tomography system using a single-frequency laser as claimed in claim 4, characterized in that: After completing the detection of a certain layer of the target region (10), the target region (10) is stepped along the z direction to repeat the detection, thereby achieving three-dimensional tomographic imaging of the target region (10).

6. The optical coherence tomography system using a single-frequency laser according to claim 1, characterized in that: The resolution of the system in the z direction is controlled by a nano-translation stage.

7. An optical coherence tomography system using a single-frequency laser according to any one of claims 1 to 6, characterized in that: The computing unit (16) is a computer.

8. The use of an optical coherence tomography system using a single-frequency laser according to any one of claims 1 to 7, characterized in that: Optical coherence tomography systems are used in the field of medical testing.

9. The use of an optical coherence tomography system using a single-frequency laser according to any one of claims 1 to 7, characterized in that: Optical coherence tomography systems are used in the field of industrial inspection.

10. The use of an optical coherence tomography system using a single-frequency laser according to any one of claims 1 to 7, characterized in that: Optical coherence tomography systems are used in the field of materials science research.

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