Small Airy spot spectrometer for optical coherence tomography

Abstract

The invention relates to the technical field of spectrometers, in particular to a small Airy spot spectrograph for optical coherence tomography, the wave band of a used light source is a near-infrared wave band, and the small Airy spot spectrograph comprises a collimation unit, a grating unit, a focus lens group and a linear array camera; the collimation unit is a large-aperture reflection-type optical fiber collimator and is used for carrying out collimation and shaping processing on interference spectrum signals acquired by the acquisition end of the SD-OCT system through light beams emitted by an optical fiber patch cord; the grating unit is a transmission-type diffraction grating and is used for carrying out diffraction light splitting on the collimated light beam to obtain light with different diffraction angles and different wavelengths; and the light beams with different wavelengths after diffraction and light splitting are focused on the light sensing surface of the linear array camera by the focusing lens group. According to the invention, the aberration is optimized, so that the performance of the SD-OCT system is close to the diffraction limit, and the roll-off degree of the SD-OCT system can be reduced; the incident beam diameter is increased, and the Airy spot radius of the system is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrometers, and in particular to a small Airy disk spectrometer for optical coherence tomography. Background Art

[0002] Optical Coherence Tomography (OCT) technology can perform three-dimensional tomographic imaging of the sample being tested and obtain information on the microstructure inside the sample. It has the characteristics of non-destructive testing, high sensitivity, high speed, high precision, and real-time imaging. Among them, spectral-domain (SD) OCT technology is an OCT technology based on a broadband light source and a fast spectrometer. SD-OCT breaks through the speed and sensitivity limitations of traditional time-domain OCT through frequency-domain spectral analysis and Fourier transform technology, and is widely used in ophthalmology, cardiology, dermatology, material defect detection, semiconductor packaging, cultural relics protection, biological research and other fields. The increasingly wide range of application scenarios has placed higher and higher demands on SD-OCT technology.

[0003] In SD-OCT spectrometers, signal intensity decreases with increasing depth, affecting image quality when penetrating deeper into the sample. This phenomenon is known as roll-off, and reducing the roll-off level of the SD-OCT system is crucial to improving imaging clarity when inspecting samples at great depths. To meet this demand, it is necessary to ensure high spectrometer imaging performance, i.e., to ensure that the spot size on the imaging detector pixel is very small, close to diffraction-limited performance. Currently, the spectrometer imaging spot size in SD-OCT systems is large, with additional aberrations, resulting in poor roll-off performance of the OCT spectrometer system. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: in order to reduce the roll-off degree of the SD-OCT system, the present invention provides a small Airy disk spectrometer for optical coherence tomography, which optimizes the aberration so that its performance is close to the diffraction limit, thereby reducing the roll-off degree of the SD-OCT system.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a small Airy disk spectrometer for optical coherence tomography, the light source band used is the near-infrared band, and includes a collimation unit, a grating unit, a focusing lens group and a linear array camera; the collimation unit is a reflective fiber collimator with an output beam diameter less than 28.7 mm, which is used to collimate and shape the interference spectrum signal obtained by the acquisition end of the SD-OCT system through the light beam emitted by the optical fiber jumper; the grating unit is a transmission diffraction grating, which is used to diffract and split the collimated light beam to obtain light of different wavelengths with different diffraction angles; the light beams of different wavelengths after diffraction and splitting are focused by the focusing lens group onto the photosensitive surface of the linear array camera.

[0006] The smaller the beam diameter, the larger the Airy disk. Preferably, the collimation unit is a reflective fiber collimator with an output beam diameter of 28.7 mm.

[0007] The interference spectrum signal obtained by the acquisition end of the SD-OCT system is emitted through a fiber optic patch cord with a numerical aperture NA of 0.14.

[0008] The focusing lens group consists of four lenses, namely the first lens, the second lens, the third lens and the fourth lens. Light beams of different wavelengths pass through the first lens, the second lens, the third lens and the fourth lens in sequence and are imaged onto the line array camera.

[0009] The first lens, the second lens, and the third lens are responsible for the main optical power of the lens group and correct aberrations. The fourth lens is mainly used to correct the field curvature of the system.

[0010] The first lens, the second lens and the third lens correct aberrations such as spherical aberration and coma.

[0011] When setting the evaluation function, the optimization weights at different aperture positions are adjusted to optimize the aberrations at the edge positions. Two different evaluation function standards, point diagram and contrast, are used to optimize the lens curvature radius, thickness, spacing between lenses, and lens materials. This allows the aberrations in each band to be optimized within the Airy disk, and the system imaging quality approaches diffraction-limited performance.

[0012] The first lens is a biconcave lens, the second lens is a plano-concave lens, the third lens is a plano-convex lens, and the fourth lens is a plano-concave lens.

[0013] The material of the first lens is H-ZPK5, the first surface curvature radius is 73.38mm, and the second surface curvature radius is 213.34mm; the material of the second lens is H-ZF88, and the second surface curvature radius is 127.1mm; the material of the third lens is H-ZLAF68N, and the second surface curvature radius is 65.13mm; the material of the fourth lens is H-ZF52GT, and the second surface curvature radius is 127.1mm; the distance between the first and second lenses is 5mm, the distance between the second and third lenses is 58.2mm, and the distance between the third and fourth lenses is 32.6mm.

[0014] The line array camera is a high-speed line array camera.

[0015] The pixel size of the high-speed line scan camera is 10 μm.

[0016] The beneficial effects of the present invention are that the small Airy disk spectrometer for optical coherence tomography of the present invention can reduce the roll-off degree of the SD-OCT system by optimizing aberrations so that its performance is close to the diffraction limit; increase the incident light beam diameter and reduce the Airy disk radius of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings and examples.

[0018] Figure 1 The present invention is a light path diagram of a small Airy disk spectrometer for optical coherence tomography.

[0019] Figure 2 The present invention discloses a point diagram of a small Airy disk spectrometer for optical coherence tomography.

[0020] Figure 2 (a), (b), and (c) are the spot diagrams for low, medium, and high wavelengths, respectively.

[0021] Figure 3 The diagram is a modulation transfer function diagram of a small Airy disk spectrometer for optical coherence tomography at high, medium and low wavelengths according to the present invention.

[0022] Figure 3 (a), (b), and (c) are the modulation transfer functions at low, medium, and high wavelengths, respectively; Figure 3 The solid line represents the modulation transfer function of the system in the meridional direction, and the dashed line represents the modulation transfer function in the sagittal direction.

[0023] Figure 4 The present invention discloses a center wavelength circled energy curve diagram of a small Airy disk spectrometer for optical coherence tomography.

[0024] Figure 4(a), (b), and (c) are the circled energy curves at low, medium, and high wavelengths, respectively; Figure 4 The black line in the figure represents the diffraction-limited energy curve, and the blue line represents the actual energy curve of the system.

[0025] In the figure, 1 is the collimating unit, 2 is the grating unit, 3 is the first lens, 4 is the second lens, 5 is the third lens, 6 is the fourth lens, and 7 is the photosensitive surface. DETAILED DESCRIPTION

[0026] 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.

[0027] The present invention is a small Airy disk spectrometer for optical coherence tomography, the light source band used is the near infrared band, such as Figure 1 As shown, the system comprises a collimator unit 1, a grating unit 2, a focusing lens assembly, and a linear scan camera. The collimator unit 1 is a reflective fiber collimator with an output beam diameter less than 28.7 mm. It is used to collimate and shape the interference spectrum signal acquired by the SD-OCT system's acquisition end through a fiber jumper with a numerical aperture of 0.14. The grating unit 2 is a transmissive diffraction grating used to diffract and split the collimated beam, generating light of different wavelengths with different diffraction angles. The beams of different wavelengths after diffraction and splitting are focused by the focusing lens assembly onto the photosensitive surface 7 of the linear scan camera. The fiber jumper and the collimator unit jointly determine the output beam diameter. The interference spectrum signal acquired by the SD-OCT system's acquisition end is emitted through the fiber jumper with a numerical aperture of 0.14. The output beam diameter of the collimator unit is preferably 28.7 mm. The smaller the beam diameter, the larger the Airy disk.

[0028] The focusing lens assembly consists of four lenses: a first lens 3, a second lens 4, a third lens 5, and a fourth lens 6. Light beams of different wavelengths pass through these lenses in sequence before being imaged onto the line scan camera. The line scan camera is a high-speed camera with a pixel size of 10μm.

[0029] The first lens 3, the second lens 4, and the third lens 5 are responsible for the main optical power of the lens group and correct aberrations. The main function of the fourth lens 6 is to correct the field curvature of the system.

[0030] The first lens 3, the second lens 4, and the third lens 5 correct aberrations such as spherical aberration and coma.

[0031] When setting the evaluation function, the optimization weights at different aperture positions are adjusted to optimize the aberrations at the edge positions. Two different evaluation function standards, point diagram and contrast, are used to optimize the lens curvature radius, thickness, spacing between lenses, and lens materials. This allows the aberrations in each band to be optimized within the Airy disk, and the system imaging quality approaches diffraction-limited performance.

[0032] The first lens 3 is a biconcave lens, the second lens 4 is a plano-concave lens, the third lens 5 is a plano-convex lens, and the fourth lens 6 is a plano-concave lens.

[0033] The material of the first lens 3 is H-ZPK5, the first surface radius of curvature is 73.38mm, and the second surface radius of curvature is 213.34mm; the material of the second lens 4 is H-ZF88, the second surface radius of curvature is 127.1mm; the material of the third lens 5 is H-ZLAF68N, the second surface radius of curvature is 65.13mm; the material of the fourth lens 6 is H-ZF52GT, the second surface radius of curvature is 127.1mm; the distance between the first lens 3 and the second lens 4 is 5mm, the distance between the second lens 4 and the third lens 5 is 58.2mm, and the distance between the third lens 5 and the fourth lens 6 is 32.6mm.

[0034] The light source band used in the spectrometer design of the present invention is the near-infrared band. The interference spectrum signal obtained by the acquisition end of the SD-OCT system is transmitted to the spectrometer part through the optical fiber jumper and finally collected by the high-speed linear array camera. Figure 1 The medium blue line represents low wavelengths, the green line represents medium wavelengths, and the red line represents high wavelengths.

[0035] To reduce the system's Airy disk radius, the incident beam diameter is increased. Interference light carrying sample depth information is collected by the acquisition end and transmitted to the spectrometer. The beam exiting the fiber patch cord is first collimated and shaped by a large-aperture reflective fiber collimator. The collimated beam is then diffracted and split by a large-scale transmissive diffraction grating, yielding light of varying wavelengths with varying diffraction angles.

[0036] After diffraction and spectral splitting, the large-diameter beams of different wavelengths are focused by the spectrometer's focusing lens assembly onto the photosensitive surface 7 of the high-speed line scan camera. The spectrometer's focusing lens assembly consists of four lenses. The large-diameter beams of different wavelengths pass sequentially through the focusing lens assembly's first lens 3, second lens 4, third lens 5, and fourth lens 6 before being imaged onto the high-speed line scan camera. The first, second, and third lenses 3, 4, and 5 provide the majority of the lens assembly's optical power and correct for aberrations such as spherical aberration and coma. The fourth lens 6 primarily corrects for field curvature.

[0037] like Figure 2Shown is a spot diagram of a small Airy disk spectrometer used for optical coherence tomography. The Airy disk radius for imaging at the central wavelength is only 3.759 μm, far smaller than the 10 μm pixel size of a high-speed line scan camera. Furthermore, the aberrations at all three wavelengths, high, medium, and low, are optimized to fit within the Airy disk, demonstrating that the system's imaging performance is near the diffraction limit.

[0038] like Figure 3 Shown are the modulation transfer functions (MTFs) of a small Airy disk spectrometer for optical coherence tomography at low, medium, and high wavelengths. The MTFs are all better than 80% at the Nyquist frequency for a 10μm pixel width, or a spatial frequency of 50 lines / mm. This corresponds to the Nyquist frequency for a 10μm pixel width.

[0039] like Figure 4 The figure shows the energy input curves at low, medium, and high wavelengths for the small Airy disk spectrometer used for optical coherence tomography. It can be seen that within the 10 μm range, the system's input energy is close to the diffraction limit.

[0040] 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 scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A small Airy disk spectrometer for optical coherence tomography, characterized in that: The light source used has a near-infrared band and comprises a collimating unit (1), a grating unit (2), a focusing lens group and a linear array camera; the collimating unit (1) is a reflective optical fiber collimator with an output beam diameter less than 28.7 mm, and is used to collimate and shape the interference spectrum signal obtained by the acquisition end of the SD-OCT system through the light beam emitted by the optical fiber jumper; the grating unit (2) is a transmission diffraction grating, and is used to diffract and split the collimated light beam to obtain light of different wavelengths with different diffraction angles; the light beams of different wavelengths after diffraction and splitting are focused by the focusing lens group onto the photosensitive surface (7) of the linear array camera.

2. The small Airy disk spectrometer for optical coherence tomography according to claim 1, wherein: The collimation unit (1) is a reflective optical fiber collimator with an output light beam diameter of 28.7 mm.

3. The small Airy disk spectrometer for optical coherence tomography according to claim 2, wherein: The interference spectrum signal obtained by the acquisition end of the SD-OCT system is emitted through a fiber optic patch cord with a numerical aperture NA of 0.

14.

4. The small Airy disk spectrometer for optical coherence tomography according to claim 1, wherein: The focusing lens group is composed of a first lens (3), a second lens (4), a third lens (5) and a fourth lens (6), a total of four lenses. Light beams of different wavelengths pass through the first lens (3), the second lens (4), the third lens (5) and the fourth lens (6) in sequence and are imaged onto the line array camera.

5. The small Airy disk spectrometer for optical coherence tomography according to claim 4, wherein: The first lens (3), the second lens (4), and the third lens (5) bear the main optical power of the lens group and correct the aberrations, and the main function of the fourth lens (6) is to correct the field curvature of the system.

6. The small Airy disk spectrometer for optical coherence tomography according to claim 5, wherein: When setting the evaluation function, the optimization weights at different aperture positions are adjusted to optimize the aberrations at the edge positions. Two different evaluation function standards, point diagram and contrast, are used to optimize the lens curvature radius, thickness, spacing between lenses, and lens materials. This allows the aberrations in each band to be optimized within the Airy disk, and the system imaging quality approaches diffraction-limited performance.

7. The small Airy disk spectrometer for optical coherence tomography according to claim 6, wherein: The first lens (3) is a biconcave lens, the second lens (4) is a plano-concave lens, the third lens (5) is a plano-convex lens, and the fourth lens (6) is a plano-concave lens.

8. The small Airy disk spectrometer for optical coherence tomography according to claim 7, wherein: The material of the first lens (3) is H-ZPK5, the first surface curvature radius is 73.38 mm, and the second surface curvature radius is 213.34 mm; the material of the second lens (4) is H-ZF88, and the second surface curvature radius is 127.1 mm; the material of the third lens (5) is H-ZLAF68N, and the second surface curvature radius is 65.13 mm; the material of the fourth lens (6) is H-ZF52GT, and the second surface curvature radius is 127.1 mm; the interval between the first lens (3) and the second lens (4) is 5 mm, the interval between the second lens (4) and the third lens (5) is 58.2 mm, and the interval between the third lens (5) and the fourth lens (6) is 32.6 mm.

9. The small Airy disk spectrometer for optical coherence tomography according to claim 1, wherein: The line array camera is a high-speed line array camera.

10. The small Airy disk spectrometer for optical coherence tomography according to claim 9, wherein: The pixel size of the high-speed line scan camera is 10 μm.

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