Large-view full-field illumination and high-resolution optical coherence tomography system

Abstract

The invention relates to the technical field of optical imaging systems, in particular to a large-view full-field illumination and high-resolution optical coherence tomography system which comprises a tunable laser, a collimation beam expander, a polarization beam splitter, an area-array camera, a sample arm system and a reference arm system. 1 / 2 wave plates are arranged behind the collimation beam expander and in front of the sample arm system, the reference arm system and the area-array camera on the polarization beam splitter, 1 / 4 wave plates are arranged between the polarization beam splitter and the collimation beam expander, 1 / 4 wave plates are arranged between the polarization beam splitter and the sample arm system and between the polarization beam splitter and the reference arm system, and a polaroid is arranged between the polarization beam splitter and the area-array camera. The sample arm system and the reference arm system are both Kepler telescope systems. According to the high-resolution imaging optical system based on the Kepler telescope system, the FF-SS-OCT imaging principle is applied, the large imaging view is guaranteed while three-dimensional high-resolution imaging is guaranteed, and the imaging time can be greatly saved.

Description

Technical Field

[0001] The present application relates to the technical field of optical imaging systems, and in particular to a large-field-of-view full-field illumination and high-resolution optical coherence tomography imaging system. Background Art

[0002] In the field of industrial defect detection, optical coherence tomography (OCT) technology is increasingly being used in various industrial scenarios due to its ability to perform three-dimensional tomographic imaging of the interior of a sample. For example, it can detect defects within lens assemblies, LCD screens, optical films, and printed circuit boards. These complex applications place increasingly stringent demands on OCT technology, such as a large field of view, high resolution, and high speed. These requirements are often difficult to achieve with a single technology, necessitating a combination of technologies to meet these diverse needs.

[0003] Among various OCT techniques, swept-source (SS) OCT uses a high-speed tunable laser to scan the sample's wavelength depth. This means that quasi-monochromatic light of different wavelengths illuminates the sample at different times, enabling high-speed scanning of the sample's depth. In the lateral direction, imaging the sample using a point-scanning method places high demands on beam deflection and focusing when imaging the sample, resulting in slow imaging speed. Full-field (FF) OCT, on the other hand, employs an area-scanning imaging method. Based on a Kepler telescope system, it illuminates the sample with a parallel, wide beam and uses an area array camera for data acquisition. This eliminates the need for beam focusing and deflection, enabling a large imaging field of view and shortening imaging time. The earliest FF-OCT technology employed a time-domain (TD) imaging scheme, using an area array camera to capture interference fringes laterally and a moving reference arm to perform tomography within the sample axially. Each depth within the sample corresponds to a set of two-dimensional interference images. Demodulation of each 2D image using a four-step phase shifting method ultimately yields information about the sample's three-dimensional structure. However, this TD-FF-OCT technology solution is difficult to achieve high-speed imaging due to the mechanical movement of the reference arm. Summary of the Invention

[0004] The technical problems to be solved by the present invention are:

[0005] To this end, the present invention provides a large-field-of-view full-field illumination and high-resolution optical coherence tomography imaging system.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A large-field-of-view, full-field illumination, high-resolution optical coherence tomography system includes a tunable laser, a collimating beam expander, a polarization beam splitter, an area array camera, a sample arm system, and a reference arm system. The tunable laser is connected to the collimating beam expander. The polarization beam splitter is arranged after the collimating beam expander and before the sample arm system, the reference arm system, and the area array camera. A 1 / 2 wave plate is arranged between the polarization beam splitter and the collimating beam expander. A 1 / 4 wave plate is arranged between the polarization beam splitter and the sample arm system and the reference arm system. A polarizer is arranged between the polarization beam splitter and the area array camera. A sample is arranged after the sample arm system. A reference arm reflector is arranged after the reference arm system. The sample arm system and the reference arm system are both configured as Kepler telescope systems.

[0008] Furthermore, the sample arm system includes a first sample arm end lens group and a second sample arm end lens group, the first sample arm end lens group is arranged on a side close to the polarization beam splitter, and the second sample arm end lens group is arranged on a side close to the sample, and the two sample arm end lens groups constitute a Kepler telescope system.

[0009] Furthermore, the reference arm system includes a first reference arm end lens group and a second reference arm end lens group, the first reference arm end lens group is arranged on a side close to the polarization beam splitter, and the second reference arm end lens group is arranged on a side close to the reference arm reflector, and the two reference arm end lens groups constitute a Kepler telescope system.

[0010] Furthermore, the Kepler telescope system includes a first lens group and a second lens group, the first lens group includes a first lens A, a second lens A, a third lens A, and a fourth lens A, and the second lens group includes a first lens B, a second lens B, and a third lens B. Along the direction from the polarization beam splitter to the sample or reference arm reflector, the first lens A, the second lens A, the third lens A, the fourth lens A, the first lens B, the second lens B, and the third lens B are arranged in sequence, and the focus of the first lens group coincides with the focus of the second lens group.

[0011] Furthermore, with the side of the lens close to the polarization beam splitter as the front surface and the side away from the polarization beam splitter as the negative surface: the front surface of the first lens A is concave, and the negative surface is a plane; the front surface of the second lens A is convex, and the negative surface is concave; the front surface of the third lens A is plane, and the negative surface is convex; the front and negative surfaces of the fourth lens A are both concave; the front surface of the first lens B is convex, and the negative surface is concave; the front and negative surfaces of the second lens B are both convex; the front surface of the third lens B is plane, and the negative surface is convex.

[0012] Furthermore, the effective focal length of the first lens group is denoted by f1, the effective focal length of the second lens group is denoted by f2, and the system magnification is k, and the effective focal lengths of the first lens group and the second lens group satisfy f2=k*f1.

[0013] Furthermore, the pixel size of the area array camera is M, and the Airy disk radius of the large field of view full field illumination and high resolution optical coherence tomography system is R Airy Satisfaction: R Airy =0.61*λ / (n*sinα)≤M, where n is the refractive index of the medium, λ is the system design wavelength, and α is the semi-aperture angle of the imaging light path at the image plane.

[0014] Furthermore, an optical fiber is connected between the tunable laser and the collimating beam expander.

[0015] The beneficial effect of the present invention is that the large-field collimated beam illumination and high-resolution imaging optical system designed based on the Kepler telescope system applies the FF-SS-OCT imaging principle, which ensures a large imaging field of view while ensuring three-dimensional high-resolution imaging, and can greatly save imaging time. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described below with reference to the accompanying drawings and examples.

[0017] Figure 1 It is a structural schematic diagram of the large-field full-field illumination and high-resolution optical coherence tomography system of the present invention.

[0018] Figure 2 This is a diagram of the illumination light path based on the Kepler telescope system in Example 1 of the present invention.

[0019] Figure 3 This is an imaging optical path diagram based on the Kepler telescope system in Example 1 of the present invention.

[0020] Figure 4 This is a spot diagram of the imaging optical path design results based on the Kepler telescope system in Example 1 of the present invention.

[0021] Figure 5 This is a diffraction circle energy diagram based on the imaging optical path design result of the Kepler telescope system in Example 1 of the present invention.

[0022] Figure 6 This is a distortion diagram of the imaging optical path design result based on the Kepler telescope system in Example 1 of the present invention.

[0023] In the figure: 1. Tunable laser; 2. Collimating beam expander; 3. 1 / 2 wave plate; 4. Polarization beam splitter; 5. 1 / 4 wave plate; 6. Reference arm system; 61. First reference arm end lens group; 62. Second reference arm end lens group; 7. Reference arm reflector; 8. Sample arm system; 81. First sample arm end lens group; 82. Second sample arm end lens group; 811. First lens A; 812. Second lens A; 813. Third lens A; 814. Fourth lens A; 821. First lens B; 822. Second lens B; 823. Third lens B; 9. Sample; 10. Polarizer; 11. Area array camera. DETAILED DESCRIPTION

[0024] The present invention will now be described in further detail with reference to the accompanying drawings, which are simplified schematic diagrams that illustrate the basic structure of the present invention in a schematic manner.

[0025] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, features defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0026] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0027] A large-field full-field illumination and high-resolution optical coherence tomography system comprises a tunable laser 1, a collimating beam expander 2, a polarization beam splitter 4, an area array camera 11, a sample arm system 8 and a reference arm system 6.

[0028] An optical fiber is connected between the tunable laser 1 and the collimating beam expander 2. A polarization beam splitter 4 is disposed between the area array camera 11, the collimating beam expander 2, the sample arm system 8, and the reference arm system 6. Specifically, the polarization beam splitter 4 is disposed after the collimating beam expander 2 and before the sample arm system 8, the reference arm system 6, and the area array camera 11. A half-wave plate 3 is disposed between the polarization beam splitter 4 and the collimating beam expander 2. A quarter-wave plate 5 is disposed between the polarization beam splitter 4 and the sample arm system 8 and the reference arm system 6. A polarizer 10 is disposed between the polarization beam splitter 4 and the area array camera 11.

[0029] Specifically, the sample arm system 8 includes a first sample arm end lens group 81 and a second sample arm end lens group 82, which are sequentially arranged between the 1 / 4 wave plate 5 and the sample 9. The reference arm system 6 includes a first reference arm end lens group 61, a second reference arm end lens group 62 and a reference arm reflector 7, which are sequentially arranged between the 1 / 4 wave plate 5 and the reference arm reflector 7. The two sample arm end lens groups and the two reference arm end lens groups respectively constitute a Kepler telescope system.

[0030] For the illumination light path (such as Figure 1 (As shown by the black solid arrow in the figure): The linearly polarized laser emitted by the tunable laser 1 passes through the optical fiber and is incident on the collimating beam expander 2. The collimated and expanded beam passes through the combination of the 1 / 2 wave plate 3 and the polarization beam splitter 4 to achieve arbitrary light intensity ratio.

[0031] The p-light transmitted from the polarization beam splitter 4 enters the sample arm system 8 and first passes through the sample arm quarter-wave plate 5, which converts linearly polarized light into circularly polarized light, ensuring uniform illumination of the sample 9 in all polarization directions. It then passes through a Kepler telescope system consisting of two sample arm lens groups before finally irradiating the sample 9. Light scattered from the sample 9 is focused by the same Kepler telescope system and then passes again through the sample arm quarter-wave plate 5 in front of the sample arm system 8. This polarization direction of the light is rotated 90 degrees (becoming s-light), preventing it from transmitting through the polarization beam splitter 4, ensuring isolation of the return light from the tunable laser 1.

[0032] The s-light reflected from the polarization beam splitter 4 enters the reference arm system 6, first passing through the quarter-wave plate 5 in front of the reference arm system 6, then sequentially passing through the Kepler telescope system consisting of two reference arm lens groups, and finally irradiating the reference arm reflector 7. The light reflected from the reference arm reflector 7 is beam-contracted by the same Kepler telescope system and then passes through the reference arm quarter-wave plate 5 again. The polarization direction of the light is rotated 90 degrees (becoming p-light), and it cannot be reflected from the polarization beam splitter 4 back to the tunable laser 1.

[0033] The return light from the sample arm system 8 and the reference arm system 6 meet at the polarization beam splitter 4. The s light returned by the sample arm system 8 is reflected by the polarization beam splitter 4, and the p light returned by the reference arm system 6 is transmitted through the polarization beam splitter 4. After passing through the polarizer 10, the two beams of light have the same polarization direction in order to ensure the maximum contrast of the interference fringes. The two beams of light interfere in front of the area array camera 11, and the interference fringes are received by the area array camera 11.

[0034] For the imaging optical path (such as Figure 1 (Indicated by the middle gray dotted arrow): The divergent light emitted by the point light source at sample 9 is converged after passing through the Kepler telescope system composed of two lens groups at the sample arm end. It then passes through the 1 / 4 wave plate 5 at the sample arm end, the polarization beam splitter 4, and the polarizer 10 in sequence before being imaged onto the area array camera 11.

[0035] Tunable laser 1 switches between quasi-monochromatic light of different wavelengths to input the FF-SS-OCT (Full Field Swept Source Optical Coherence Tomography) system. By scanning the wavelength, longitudinal structural information of sample 9 is acquired in the frequency domain. Then, spatial structural information along the depth direction of sample 9 is obtained through inverse Fourier transform. For transverse structural information of sample 9, the system uses full-field illumination for interferometric imaging. Each time the tunable laser 1 scans a narrowband laser of a specific wavelength, the area array camera 11 of the interferometric illumination imaging system captures a two-dimensional interference fringe image, completing the acquisition of two-dimensional transverse information and thus enabling the collection of three-dimensional raw data of sample 9.

[0036] The overall system structure is a Michelson interferometer, with the sample arm system 8 and the reference arm system 6 adopting symmetrical structures to minimize the effects of dispersion on imaging. Regarding the illumination optical paths of the sample arm system 8 and the reference arm system 6, the incident light in the illumination optical path is expanded through a Kepler telescope system. Based on the principle of optical path reversibility, the return light follows the same trajectory as the incident light but in the opposite direction, and is then contracted after passing through the Kepler telescope system. Based on the Michelson interference principle, the return light from the sample arm system 8 and the return light from the reference arm system 6 merge before reaching the area array camera 11, introducing a certain optical path difference and causing interference. Regarding the imaging optical path, light emitted from the point source at the sample 9 passes through the sample arm's Kepler telescope system before being imaged onto the area array camera 11.

[0037] It should be noted that the Kepler telescope systems composed of the two sample arm end lens groups and the two reference arm end lens groups have the same structure. The first sample arm end lens group 81 and the first reference arm end lens group 61 have the same structure and are the first lens group. The second sample arm end lens group 82 and the second reference arm end lens group 62 have the same structure and are the second lens group.

[0038] Specifically, the first lens group includes a first lens A811, a second lens A812, a third lens A813, and a fourth lens A814; the second lens group includes a first lens B821, a second lens B822, and a third lens B823. Along the direction from the polarization beam splitter 4 to the sample 9 or the reference arm reflector 7, the first lens A811, the second lens A812, the third lens A813, the fourth lens A814, the first lens B821, the second lens B822, and the third lens B823 are arranged in sequence. Among them, the side of the lens close to the polarization beam splitter 4 is the front surface, and the side away from the polarization beam splitter 4 is the negative surface: the front surface of the first lens A811 is concave, and the negative surface is a plane; the front surface of the second lens A812 is convex, and the negative surface is concave; the front surface of the third lens A813 is a plane, and the negative surface is convex; the front and negative surfaces of the fourth lens A814 are both concave; the front surface of the first lens B821 is convex, and the negative surface is concave; the front and negative surfaces of the second lens B822 are both convex; the front surface of the third lens B823 is a plane, and the negative surface is convex.

[0039] The light emitted from the point light source at sample 9 passes through the third lens B823, the second lens B822, the first lens B821, the fourth lens A814, the third lens A813, the second lens A812, and the first lens A811 of the Kepler telescope system in sequence, and then passes through the polarization beam splitter 4 to be imaged onto the area array camera 11.

[0040] Example 1

[0041] In this embodiment, the central wavelength of the tunable laser 1 is around 775 nm, and the 3 dB spectral bandwidth is at least 36 nm to ensure that the longitudinal resolution of the system is no higher than 10 μm. Therefore, the wavelength range of the optical path design of the Kepler telescope system is determined to be 757 nm to 793 nm.

[0042] The area array camera 11 has a format size of 4096×3072. The system's lateral resolution is guaranteed to be no greater than 10 μm, while the diameter of the expanded illumination beam is no less than the diagonal length of the area array camera 11. The appropriate system magnification factor k is set to 1.62. The effective focal length of the first lens group is denoted by f1, and the effective focal length of the second lens group is denoted by f2. Here, f2 = k*f1.

[0043] The pixel size M of the area array camera 11 is 5.5 μm. To ensure that the system meets the sampling theorem and has sufficient imaging contrast, the Airy disk radius R Airy No larger than the pixel size of an area array camera, i.e. the radius of the Airy disk R Airy=0.61*λ / (n*sinα)≤M, where n is the refractive index of the medium. Since this telescope system is located in air, n=1. λ is the system design wavelength, and α is the semi-aperture angle of the imaging light path at the image plane. Based on the above design principles, the curvature radius of each lens and the spacing between lens planes that make up the Kepler telescope system are optimized. Specifically, the parameters of the lenses in this embodiment of the Kepler telescope system are shown in Table 1:

[0044] Table 1 Kepler telescope system lens parameters

[0045]

[0046]

[0047] Reference Figure 3 , Figure 3 The a-picture is the center field of view, the b-picture is the middle field of view, and the c-picture is the edge field of view. The point diagram of the imaging optical path design result based on the Kepler telescope system is shown in the figure below. Figure 4 As shown, the Airy disk radii of the images from the shortest wavelength (757nm), central wavelength (775nm), and longest wavelength (793nm) point sources are 5.183μm, 5.306μm, and 5.429μm, respectively, all smaller than the 5.5μm pixel size, satisfying the Nyquist sampling theorem. Furthermore, the root mean square error (RMS) of the spot diagrams obtained at different positions on the image plane for the three wavelengths is smaller than the Airy disk radius, indicating that the system's imaging is within the diffraction limit.

[0048] like Figure 5 The figure shows a schematic diagram of the diffraction-enclosed energy based on the imaging optical path design results of the Kepler telescope system. It can be seen from the figure that the pixel enclosed energy at the 0.00mm position on the center field image plane and the 7.00mm position on the middle field image plane is greater than 80%, and the pixel enclosed energy at the 14.00mm position on the edge field image plane is greater than 50%.

[0049] like Figure 6 The figure shows the distortion results of the imaging optical path design based on the Kepler telescope system. The maximum wavelength introduces a maximum distortion of 0.1792%.

[0050] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical spirit of this invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A large-field full-field illumination, high-resolution optical coherence tomography imaging system, characterized in that: The invention comprises a tunable laser (1), a collimating beam expander (2), a polarization beam splitter (4), an array camera (11), a sample arm system (8) and a reference arm system (6), wherein the tunable laser (1) is connected to the collimating beam expander (2), the polarization beam splitter (4) is arranged after the collimating beam expander (2) and before the sample arm system (8), the reference arm system (6) and the array camera (11), and a polarization beam splitter (4) is arranged between the collimating beam expander (2). A 1 / 2 wave plate (3) is provided, a 1 / 4 wave plate (5) is provided between the polarization beam splitter (4) and the sample arm system (8) and the reference arm system (6), a polarization plate (10) is provided between the polarization beam splitter (4) and the area array camera (11), a sample (9) is provided behind the sample arm system (8), a reference arm reflector (7) is provided behind the reference arm system (6), and the sample arm system (8) and the reference arm system (6) are both provided as Kepler telescope systems.

2. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 1, characterized in that: The sample arm system (8) comprises a first sample arm end lens group (81) and a second sample arm end lens group (82), wherein the first sample arm end lens group (81) is arranged on a side close to the polarization beam splitter (4), and the second sample arm end lens group (82) is arranged on a side close to the sample (9), and the two sample arm end lens groups constitute a Kepler telescope system.

3. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 2, characterized in that: The reference arm system (6) comprises a first reference arm end lens group (61) and a second reference arm end lens group (62), wherein the first reference arm end lens group (61) is arranged on a side close to the polarization beam splitter (4), and the second reference arm end lens group (62) is arranged on a side close to the reference arm reflector (7), and the two reference arm end lens groups constitute a Kepler telescope system.

4. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 3, characterized in that: The Keplerian telescope system includes a first lens group and a second lens group, wherein the first lens group is a first sample arm end lens group (81) or a first reference arm end lens group (61), and the second lens group is a second sample arm end lens group (82) or a second reference arm end lens group (62). The first lens group includes a first lens A (811), a second lens A (812), a third lens A (813), and a fourth lens A (814). The second lens group includes a first lens B (821), a second lens B (822), and a third lens B (823). Along the direction from the polarization beam splitter (4) to the sample (9) or the reference arm reflector (7), the first lens A (811), the second lens A (812), the third lens A (813), the fourth lens A (814), the first lens B (821), the second lens B (822), and the third lens B (823) are arranged in sequence.

5. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 4, characterized in that: The side of the lens close to the polarization beam splitter (4) is the front side, and the side away from the polarization beam splitter (4) is the negative side: the front side of the first lens A (811) is a concave surface, and the negative side is a plane surface; the front side of the second lens A (812) is a convex surface, and the negative side is a concave surface; the front side of the third lens A (813) is a plane surface, and the negative side is a convex surface; the front side and the negative side of the fourth lens A (814) are both concave surfaces; the front side of the first lens B (821) is a convex surface, and the negative side is a concave surface; the front side and the negative side of the second lens B (822) are both convex surfaces; the front side of the third lens B (823) is a plane surface, and the negative side is convex.

6. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 5, characterized in that: The effective focal length of the first lens group is denoted by f1, the effective focal length of the second lens group is denoted by f2, the system magnification is k, the effective focal lengths of the first lens group and the second lens group satisfy f2=k*f1, and the focus of the first lens group coincides with the focus of the second lens group.

7. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 5, characterized in that: The pixel size of the area array camera (11) is M, and the Airy disk radius R of the large-field full-field illumination and high-resolution optical coherence tomography system is Airy Satisfaction: R Airy =0.61*λ / (n*sinα)≤M, where n is the refractive index of the medium, λ is the system design wavelength, and α is the semi-aperture angle of the imaging light path at the image plane.

8. The large-field full-field illumination, high-resolution optical coherence tomography imaging system according to claim 1, characterized in that: An optical fiber is connected between the tunable laser (1) and the collimating beam expander (2).

Images