Imaging optical system of spectrum confocal microendoscope

Abstract

The utility model discloses an imaging optical system of a spectrum confocal microendoscope. The imaging optical system comprises an object plane, a front lens group, a transition lens, a rear lens group and an image plane, the front lens group comprises a spherical positive lens and two spherical negative lenses, and is used for correcting distortion and converging light beams; the transition lens is an aspheric positive lens and is used for correcting spherical aberration; the rear lens group comprises two spherical negative lenses, corrects field curvature and converges on an image plane for imaging. The imaging optical system provided by the utility model has a wide view field of 600 microns, realizes large-depth, wide-view-field and high-resolution microscopic endoscopic imaging, can detect section information of different depths, and obtains more comprehensive tissue information; the system is small in size, the caliber is only 2.8 mm, and the optical performance of clinical diagnosis can be met; the system is compact and simple in structure, easy to install and adjust and wide in application prospect.

Description

Technical Field

[0001] This utility model relates to the field of optical technology, specifically to an imaging optical system for a spectral confocal microendoscopy. Background Technology

[0002] Optical section microscopy is a powerful tool in biological research, and confocal microscopy is often the preferred tool. Because confocal endoscopes offer higher magnification and resolution than traditional endoscopes, and because they can perform in vivo and real-time imaging of various tissues, cells, molecules, and even bacteria with miniature probes, confocal endoscopy has become an important tool in clinical and research applications. However, it still has some limitations in clinical applications. In the clinical application of early gastric cancer diagnosis, once the tumor penetrates deep into the submucosa, there is a risk of lymph node metastasis. Therefore, it is necessary to obtain information from the submucosal layer of the tissue. Clinically, there is an urgent need for tools that can provide sufficient imaging depth to assess the invasive depth of early gastric tumors. However, traditional confocal microscopy techniques are excited by a single wavelength, which can only image at a specific tissue depth, and only one depth plane can be imaged at a time. Therefore, traditional confocal microscopy techniques require mechanical scanning to achieve 3D imaging, which is slow and cannot meet the clinical needs of real-time 3D imaging. Spectral confocal technology can achieve high-resolution, rapid, multi-depth tomographic imaging. Compared to traditional confocal microscopes, spectral confocal microscopes can achieve multi-wavelength and multi-depth imaging without any mechanical axial scanning. However, due to limitations in lens manufacturing processes, it is difficult to simultaneously meet the requirements of small size, large chromatic focal shift, and small spherical aberration. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies by providing an imaging optical system for a spectral confocal microendoscopy system that features deep imaging depth, high dispersion linearity, large field of view, simple and compact structure, and ease of fabrication and assembly.

[0004] The technical solution adopted in this utility model is to provide an imaging optical system for a spectral confocal microendoscopy system, which includes an object plane, a front mirror group, a transition mirror, a rear mirror group, and an image plane. The front mirror group is a three-piece near-concentric symmetrical structure, consisting of a spherical positive lens, a first spherical negative lens, and a second spherical negative lens in sequence according to the direction of light incidence. The radii of curvature of each lens surface are R21, R22, R31, R32, R41, and R42, respectively, satisfying the conditions 0.9mm≤R21≤2.3mm, -181mm≤R22≤-180mm, -4mm≤R31≤-3mm, -20.2mm≤R32≤-19.2mm, -3.8mm≤R41≤-3.1mm, and -8.2mm≤R42≤-7.4mm. The transition mirror includes a... The front and rear surfaces of the aspherical positive lens are both even-order aspherical; the radii of curvature of the front and rear surfaces are R51 and R52 respectively, satisfying the conditions 1.7mm≤R51≤2.1mm and -5.8mm≤R52≤-5.4mm respectively; the rear lens group includes two concentric spherical negative lenses; namely, the first spherical negative lens and the second spherical negative lens, the rear surface of the second spherical negative lens is a plane; according to the incident direction of light, the radii of curvature of the remaining surfaces of each lens are R61, R62 and R71 respectively, satisfying the conditions 3.6mm≤R61≤4.2mm, 1mm≤R62≤1.5mm and -5.2mm≤R71≤-4.2mm respectively; the aperture stop of the imaging optical system is set at the front surface of the first spherical negative lens (3) of the front lens group.

[0005] The front and rear surfaces of the aspherical positive lens are both aspherical. A Cartesian coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light ray is the positive Z-axis, the positive Y-axis is upward, and the positive X-axis is perpendicular to the paper and inward. The equation for the sag Z of its even-order aspherical surface is:

[0006] ,

[0007] Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i It is the coefficient of the monomial;

[0008] The front surface of the aspherical positive lens (5) has -2.4≤k≤0.4, and the coefficients of each monomial satisfy the following conditions: , , , , , .

[0009] The back surface of the aspherical positive lens (5) has -33.7≤k≤-31.7, and the coefficients of each monomial satisfy the following conditions: , , , , , .

[0010] This utility model provides an imaging optical system for a spectral confocal microendoscopy system, wherein the numerical aperture of the system object side ranges from 0.28 to 0.32, the field of view of the object side ranges from 0 mm to 0.6 mm, the total length L of the system ranges from 9.5 mm to 10.5 mm, and the aperture D of the system ranges from 2.8 mm to 3.2 mm.

[0011] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0012] 1. This utility model achieves an approximately linear relationship between axial chromatic shift and wavelength by optimizing the optical structure of the lens group and strictly controlling the axial positional relationship between different depths of focusing for each wavelength, thus ensuring the consistency of sensitivity and measurement accuracy within the measurement range.

[0013] 2. The imaging optical system provided by this utility model adopts an improved Cook three-piece structure in the front lens group, which has a fine aberration correction function, making its intrinsic aberration small and having little impact on the aberration of the subsequent optical group, effectively reducing the impact on distortion.

[0014] 3. The imaging optical system provided by this utility model has a concentric structure for its rear lens group, which further corrects field curvature through a flat field thick lens; the three lens groups are designed with a joint structure optimization, which effectively corrects the problem that aberrations such as field curvature, astigmatism and distortion increase with the increase of field of view, and achieves an ultra-wide field of view of 600μm, thereby obtaining more comprehensive tissue information; compared with the existing spectral confocal endoscopic imaging system, the field of view has been significantly improved.

[0015] 4. The imaging optical system provided by this invention places the aperture stop in front of the aspherical lens, which can accurately suppress spherical aberration without affecting other aberrations. The selection of the aspherical position enhances the system's ability to balance various geometric aberrations, suppresses residual spherical aberration in the front lens group, and compensates for coma and distortion in the rear lens group, effectively improving the overall imaging resolution of the system. Compared with existing near-infrared microscopic endoscopy imaging systems, the imaging quality is significantly improved. For the commonly used 12μm pixel size of near-infrared detectors in the 1000nm-1500nm band, this invention achieves an optical transfer function greater than 0.6 across the entire field of view in the 1μm to 1.5μm working band at 42lp / mm, demonstrating excellent imaging quality. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the structure of the spectral confocal microendoscopic imaging optical system provided in this embodiment of the present invention;

[0017] In the diagram, 1. Object plane; 11. Front lens group; 2. Spherical positive lens of the front lens group; 3. First spherical negative lens of the front lens group; 4. Second spherical negative lens of the front lens group; 22. Transition lens; 5. Fourth aspherical positive lens; 33. Rear lens group; 6. First spherical negative lens of the rear lens group; 7. Second spherical negative lens of the rear lens group; 8. Image plane;

[0018] Figure 2 This is a diagram of the focused light spot pattern of the full field of view and full working wavelength of the spectral confocal microendoscopic imaging optical system provided in this embodiment of the present invention;

[0019] Figure 3 This is a color focus shift curve of the spectral confocal microendoscopic imaging optical system provided in this embodiment of the present invention;

[0020] Figure 4 (a), (b), and (c) are the MTF curves of the spectral confocal microendoscopic imaging optical system provided in the embodiments of this utility model;

[0021] Figure 5 (a), (b) and (c) are optical path difference curves of the spectral confocal microendoscopic imaging optical system provided in this embodiment of the present invention at four fields of view in the image direction. Detailed Implementation

[0022] The technical solution of this utility model will be further described below with reference to the accompanying drawings and embodiments. Example 1:

[0023] This embodiment provides an imaging optical system for a spectral confocal microendoscopy system, which consists of six lenses. The system has an object-side numerical aperture of 0.3, a magnification of 2x for the micro-microscope objective, and an operating wavelength of 1000–1500 nm. Since the object plane of the microscope objective is connected to the end face of the fiber optic bundle within the entire endoscope probe, the effective field of view achievable by the microscope objective can be calculated to be 600 μm based on the light-transmitting aperture of the fiber optic bundle.

[0024] The performance parameters of the microendoscopy provided in this embodiment are shown in Table 1.

[0025] Table 1:

[0026] .

[0027] See appendix Figure 1This is a schematic diagram of the structure of the microscopic endoscope imaging optical system provided in this embodiment. According to the direction of light incidence, the optical elements are as follows: object plane 1, front mirror group 11, transition mirror 22, rear mirror group 33 and image plane 8.

[0028] The front lens group 11 is a three-element near-concentric symmetrical structure. According to the direction of light incidence, it consists of a spherical positive lens 2, a first spherical negative lens 3, and a second spherical negative lens 4. The radii of curvature of each lens surface are R21, R22, R31, R32, R41, and R42, respectively, satisfying the conditions 0.9mm≤R21≤2.3mm, -181mm≤R22≤-180mm, -4mm≤R31≤-3mm, -20.2mm≤R32≤-19.2mm, -3.8mm≤R41≤-3.1mm, and -8.2mm≤R42≤-7.4mm.

[0029] The transition mirror 22 is an aspherical positive lens 5, whose front and rear surfaces are both even-order aspherical surfaces; the radii of curvature of the front and rear surfaces are R51 and R52 respectively, satisfying the conditions 1.7mm≤R51≤2.1mm and -5.8mm≤R52≤-5.4mm respectively.

[0030] The rear lens group 33 includes two concentric spherical negative lenses: a first spherical negative lens 6 and a second spherical negative lens 7, the rear surface of the second spherical negative lens 7 being a plane; according to the incident direction of light, the radii of curvature of the remaining surfaces of each lens are R61, R62 and R71, respectively, satisfying the conditions 3.6mm≤R61≤4.2mm, 1mm≤R62≤1.5mm, and -5.2mm≤R71≤-4.2mm.

[0031] The aperture stop of the imaging optical system is set on the front surface of the first spherical negative lens 3 of the front lens group.

[0032] In this embodiment, the front surface of the aspherical positive lens 5 is an even-order aspherical surface. A Cartesian rectangular coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light is the positive Z-axis, the positive Y-axis is parallel to the paper and upwards, and the positive X-axis is perpendicular to the paper and outwards. The equation for the height Z of the even-order aspherical surface is:

[0033] ,

[0034] Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i These are the coefficients of the monomials; where k = -1.468, and the coefficients of each monomial are respectively... , , , , , .

[0035] In this embodiment, the rear surface of the aspherical positive lens 5 is an even-order aspherical surface. A Cartesian rectangular coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light is the positive Z-axis, the positive Y-axis is parallel to the paper and upwards, and the positive X-axis is perpendicular to the paper and outwards. The equation for the height Z of the even-order aspherical surface is:

[0036] ,

[0037] Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i These are the coefficients of the monomials; where k = -32.798, and the coefficients of each monomial are respectively... , , , , , .

[0038] The specific structural parameters of each optical element in this embodiment are shown in Table 2.

[0039] Table 2:

[0040] .

[0041] In this embodiment, the microscope objective is used for imaging. The object plane is the end face of the fiber bundle, and the light rays pass sequentially through the front mirror group 11, the transition mirror 22, and the rear mirror group 33. The front mirror group corrects the distortion of the incident light rays in the near-infrared broadband band of 1000nm to 1500nm and converges the beam to the transition mirror. The transition mirror has an aspherical structure on its front and rear surfaces to further correct the residual aberration of the incident beam and suppress the residual spherical aberration of the front mirror group. At the same time, it compensates for the coma and distortion of the rear mirror group. The imaging beam processed by the transition mirror is then converged by the rear mirror group to the image plane, resulting in a large chromatic focal shift of more than 1mm. Finally, the image is formed on the image plane, which is the cross-section of the human tissue at different depths.

[0042] The imaging optical system provided in this embodiment focuses different wavelengths onto image planes at different depths, i.e., the imaging depth in the stomach tissue. Based on the principle of light reversibility, light reflected from tissues at different depths will be reflected to the object plane and transmitted through the fiber optic bundle, thereby obtaining images of cross-sections at different depths in the stomach tissue, thus constructing an overall three-dimensional image.

[0043] See appendix Figure 2It is a ray tracing dot plot of light passing through the imaging optical system of the micro-endoscope provided in this embodiment. In the figure, the root mean square radius of the dot plots at each wavelength corresponding to the five fields of view of 0mm (a), 0.1mm (b), 0.2mm (c), 0.24mm (d) and 0.3mm (e) is less than 4.95μm, and the geometric radius of the dot plots is less than 15.00μm, indicating good imaging quality.

[0044] See appendix Figure 3 This is the chromatic focus shift curve of the imaging optical system of the microendoscopy provided in this embodiment. The axial dispersion and wavelength are linearly fitted using the least squares method, and the result is as follows: Figure 3 As shown, the axial chromatic focal shift of the dispersive objective is 1.02 mm, indicating that the system achieves deep-depth detection. Hollow circles in the figure represent actual data points, and the solid line is the fitted line representing the relationship between focal shift and wavelength. The fitted equation for the relationship between focal shift (axial dispersion δ) and wavelength (λ) is: Linearity determination coefficient R ２ The value of 0.9994 indicates that the designed dispersive objective lens has an excellent dispersion-wavelength linear relationship, which well guarantees the consistency of sensitivity within the measurement range and the accuracy during actual measurement.

[0045] See appendix Figure 4 This figure shows the MTF (Mean Transfer Function) curves of the imaging optical system of the microendoscopy provided in this embodiment for each field of view on the corresponding image plane. In the figure, figures (a), (b), and (c) correspond to the MTF curves of all fields of view of the microendoscopic imaging system provided in this embodiment at wavelengths of 1 μm, 1.25 μm, and 1.5 μm, respectively. Figure 4 As can be seen, the optical transfer function of the entire field of view in the 1μm to 1.5μm working band at 70lp / mm is greater than 0.3, close to the diffraction limit, and the curve is smooth and compact, indicating that the system has clear and uniform imaging and good imaging quality in the entire band and the entire field of view.

[0046] See appendix Figure 5 This is a graph showing the optical path difference curves of the imaging optical system of the microendoscopy provided in this embodiment at three fields of view in the image direction. In the graph, (a), (b), and (c) correspond to the optical path difference curves of the microendoscopic imaging system provided in this embodiment at the image planes with fields of view of 0mm (a), 0.2mm (b), and 0.3mm (c), respectively. Figure 5 The vertical axis in the figures is ±0.25λ. Among them, the curve corresponding to the 1.5μm wavelength in Figure (c) has the largest optical path difference, which can reach a maximum of 0.21λ at the edge of the pupil. The optical path difference of the other curves is less than 0.25λ within the pupil range, indicating that the imaging optical system of the micro-endoscope has reached near-diffraction-limited performance.

Claims

1. An imaging optical system for a spectral confocal microendoscopy system, characterized in that: It includes the object plane (1), the front lens group (11), the transition lens (22), the rear lens group (33), and the image plane (8); The front lens group (11) is a three-piece near-concentric symmetrical structure. According to the direction of light incidence, it consists of a spherical positive lens (2), the first spherical negative lens (3) of the front lens group, and the second spherical negative lens (4) of the front lens group. The radii of curvature of each lens surface are R21, R22, R31, R32, R41, and R42, respectively, satisfying the conditions 0.9mm≤R21≤2.3mm, -181mm≤R22≤-180mm, -4mm≤R31≤-3mm, -20.2mm≤R32≤-19.2mm, -3.8mm≤R41≤-3.1mm, and -8.2mm≤R42≤-7.4mm. The transition lens (22) includes an aspherical positive lens (5), the front and rear surfaces of which are even-order aspherical surfaces. The curvature of the front and rear surfaces is... The radii are R51 and R52 respectively, satisfying the conditions 1.7mm≤R51≤2.1mm and -5.8mm≤R52≤-5.4mm respectively; the rear lens group (33) includes two concentric spherical negative lenses; the rear lens group consists of the first spherical negative lens (6) and the second spherical negative lens (7), the rear surface of the second spherical negative lens (7) is a plane; according to the incident direction of light, the radii of curvature of the remaining surfaces of each lens are R61, R62 and R71 respectively, satisfying the conditions 3.6mm≤R61≤4.2mm, 1mm≤R62≤1.5mm and -5.2mm≤R71≤-4.2mm respectively; the aperture stop of the imaging optical system is set at the front surface of the first spherical negative lens (3) of the front lens group.

2. The imaging optical system of a spectral confocal microendoscopy according to claim 1, characterized in that: The front and rear surfaces of the aspherical positive lens (5) are both aspherical. A Cartesian rectangular coordinate system is constructed with the intersection of the lens surface and the optical axis as the origin. The incident direction of the light is the positive Z-axis, the positive Y-axis is upward, and the positive X-axis is perpendicular to the paper and inward. The equation for the sag of its even-order aspherical surface Z is: ， Where c is the curvature; r is the radius; k is the quadratic surface coefficient; a i It is the coefficient of the monomial; The front surface of the aspherical positive lens (5) has -2.4≤k≤0.4, and the coefficients of each monomial satisfy the following conditions: , , , , , ; The back surface of the aspherical positive lens (5) has -33.7 ≤ k ≤ -31.7, and the coefficients of each monomial satisfy the following conditions: , , , , , .

3. The imaging optical system of a spectral confocal microendoscopy according to claim 1, characterized in that: The system's object-side numerical aperture ranges from 0.28 to 0.32, and the object-side field of view ranges from 0 mm to 0.6 mm. The system's total length L ranges from 9.5 mm to 10.5 mm, and the system's aperture D ranges from 2.8 mm to 3.2 mm.

Images