Miniature endoscope lens suitable for label-free quantitative phase microscopic imaging

Abstract

The invention relates to the technical field of medical equipment, in particular to an endoscope lens which sequentially comprises a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens from an object side to an image side along an optical axis. Each lens is provided with an object side surface which faces the object side and enables imaging light to pass through and an image side surface which faces the image side and enables the imaging light to pass through; the first lens has a positive refractive index, the second lens has a positive refractive index or a negative refractive index, the third lens has a positive refractive index, the fourth lens has a negative refractive index, the fifth lens has a positive refractive index, and the sixth lens has a negative refractive index. The invention can be used for label-free quantitative phase microscopic imaging, and can avoid the problems of adverse reaction and sequelae caused by the use of a fluorescent agent in a fluorescent confocal endoscope; a special dispersion glass material and a strong and weak dispersion glass material are combined to eliminate chromatic aberration, so that the near 100nm broadband achromatic effect is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of medical equipment, and in particular to an endoscope lens. Background Art

[0002] Early diagnosis of digestive tract diseases is crucial. With the rapid development of endoscopic technology, optical endoscopes play a vital role in the detection of digestive tract diseases. They provide diagnostic information from the macroscopic to the cellular level through different imaging techniques. As a traditional detection method, white light endoscopes use white light illumination to observe the internal structure of the digestive tract. Although it is easy to operate and low in cost, its resolution is limited and its ability to identify tiny lesions is insufficient. In contrast, optical endoscopes with cellular resolution, such as fluorescence confocal endoscopes, can provide more detailed cellular-level imaging, thereby improving diagnostic efficiency, which is of great significance for the diagnosis of early cancer.

[0003] Quantitative phase microscopy is an imaging technique that uses phase changes of light waves to obtain sample information. The light source of the quantitative phase microscopy system used in the present invention is a broadband light source with a bandwidth of about 100nm. It uses a broadband light source with a shorter coherence length to produce low coherence interference, thereby achieving high-resolution imaging. In comparison, fluorescence confocal microscopy uses a laser beam to point illuminate and scan the sample, and collects fluorescence signals for imaging. The system light source band only needs to consider the excitation wavelength and emission wavelength of the fluorescent substance. The bandwidth is generally narrow, about tens of nanometers, and the achromatic ability of the micro-objective lens is required to be low. Therefore, the chromatic aberration caused by the non-monochromaticity of the broadband light source needs to be considered when designing the micro-objective lens. In addition, fluorescence microscopy requires special fluorescent staining of the in vivo tissue in advance. In some cases, the fluorescent agent may affect the normal function of the tissue and is not easy to remove after use. Summary of the invention

[0004] The invention provides a micro endoscope lens suitable for label-free quantitative phase microscopic imaging, which can be used for label-free quantitative phase microscopic imaging.

[0005] The present invention provides the following technical solutions:

[0006] A micro endoscope lens for label-free quantitative phase microscopy imaging, characterized in that it includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens in order from the object side to the image side along the optical axis, each lens having an object side surface facing the object side and allowing imaging light to pass through, and an image side surface facing the image side and allowing imaging light to pass through;

[0007] The first lens has a positive refractive power, the second lens has a positive refractive power or a negative refractive power, the third lens has a positive refractive power, the fourth lens has a negative refractive power, the fifth lens has a positive refractive power, and the sixth lens has a negative refractive power.

[0008] Furthermore, the second lens is made of special dispersion material.

[0009] Furthermore, the second lens is a biconvex lens.

[0010] Furthermore, both the image-side surface and the object-side surface of the second lens are aspherical surfaces.

[0011] Furthermore, the third lens and the fourth lens are double-cemented lenses, which are composed of a strong dispersion material and a weak dispersion material.

[0012] Furthermore, the first lens is a crescent lens, the third lens is a biconvex lens, and the object side surface and the image side surface of the fourth lens are concave surfaces.

[0013] Furthermore, the fifth lens is a biconvex lens, and the object side surface of the fifth lens is an aspherical surface.

[0014] Furthermore, the sixth lens is a biconcave lens.

[0015] Furthermore, the refractive index of the material used for the sixth lens is similar to that of the fifth lens, but the dispersion coefficient is different.

[0016] Furthermore, there is a lens without refractive power on the optical axis between the object side and the first lens for generating system interference.

[0017] The beneficial effects of the present invention are as follows: a micro endoscope lens suitable for label-free quantitative phase microscopy imaging of the present invention can be used for label-free quantitative phase microscopy imaging, and can avoid the problem of adverse reactions and sequelae caused by the use of fluorescent agents in fluorescence confocal endoscopes; a combination of positive and negative lenses, spherical lenses and aspherical lenses is adopted to balance various image quality requirements while ensuring a small size to obtain the optimal choice; in a further technical scheme, label-free phase microscopy imaging technology requires the use of 100nm broadband light to achieve low-coherence interference and obtain the phase information required for imaging. Although the broadband light source provides the required phase information, it also introduces imaging problems such as dispersion. A special dispersion glass material and a combination of strong and weak dispersion glass materials are used to eliminate chromatic aberration, thereby achieving a broadband achromatic effect of nearly 100nm. This design optimizes the imaging performance in the near-infrared band, improves the quality of biological tissue endoscopic imaging, and enables phase microscopy imaging technology to be more widely used in the biomedical field. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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:

[0019] Figure 1 Schematic diagram of the principle of a micro endoscope lens suitable for label-free quantitative phase microscopy;

[0020] Figure 2 A schematic diagram of the structure of a micro endoscope lens suitable for label-free quantitative phase microscopy;

[0021] Figure 3 Schematic diagram of diffuse spots where light beams at three different positions of the object side of the embodiment converge on the image plane;

[0022] Figure 4 is the image-side MTF curve of the embodiment;

[0023] Figure 5 is the image-side OPD curve of the embodiment;

[0024] Figure 6 1 and 1 are image field curvature (a) and distortion (b) curves of the embodiment. DETAILED DESCRIPTION

[0025] The specific implementation of the present invention will be described below in conjunction with the accompanying drawings.

[0026] The micro endoscope lens applicable to label-free quantitative phase microscopy imaging of this embodiment includes an interference module and an objective lens module.

[0027] See also Figure 2 The objective lens module includes a first lens 1, a second lens 2, a third lens 3, a fourth lens 4, a fifth lens 5 and a sixth lens 6 in order from the object side to the image side along the optical axis, each lens having an object side surface facing the object side and allowing imaging light to pass through, and an image side surface facing the image side and allowing imaging light to pass through;

[0028] The interference module includes a zeroth lens 0 disposed on the optical axis between the object side and the first lens, which is used to generate system interference, and can use a lens without refractive index such as a flat glass slide, and the material can be selected from H-K9L glass. In some embodiments, the flat glass slide and the objective lens module are integrated into the micro endoscope head.

[0029] The first lens 1 has a positive refractive power and can be a crescent-shaped convex lens with a convex image side surface 12 to focus the divergent light beam while correcting the spherical aberration caused by the zeroth lens 0.

[0030] The second lens 2 has a positive refractive power or a negative refractive power, and is used to further expand the aperture of the micro objective lens to ensure that the object field of view can reach 300μm; at the same time, it is made of a material with a special dispersion effect, such as CaF2 glass, to correct chromatic aberration and achieve apochromatism; in this embodiment, the second lens 2 uses a biconvex lens with a positive refractive power, and its image side surface 21 and object side surface 22 are both aspherical surfaces, which are used to correct aberration and improve image quality.

[0031] The third lens 3 and the fourth lens 4 are double cemented lenses, the third lens 3 has a positive refractive power, the fourth lens 4 has a negative refractive power, and a combination of a strong dispersion glass material and a weak dispersion glass material is used to further achieve achromatism. The third lens 3 is a biconvex lens, and its object side surface 31 and image side surface 32 are both convex surfaces, and the light aperture is controlled to be less than 2mm. The object side surface 41 and image side surface 42 of the fourth lens 4 are concave surfaces, and the image side surface 32 of the third lens 3 and the object side surface 41 of the fourth lens 4 share a surface.

[0032] The fifth lens 5 has a positive refractive power and may be a biconvex lens. The object side surface 51 of the fifth lens is an aspherical surface.

[0033] The sixth lens 6 has a negative refractive power, its object side surface 61 is convex, and its image side 62 is concave in the optical axis region. The sixth lens 6 is made of glass material with a similar refractive index to the fifth lens 5 but a different dispersion coefficient, which is conducive to further correcting phase aberration.

[0034] The data of the curvature radius, glass thickness, material, diameter, etc. of each component of this embodiment are shown in Table 1, where a represents an aspherical surface. The aspherical coefficients are shown in Table 2, where the surface 51 has no second-order coefficient.

[0035] Table 1 Specific parameters of each component

[0036]

[0037]

[0038] Table 2 Specific coefficients of various aspherical surfaces

[0039]

[0040] See also Figure 1In the present embodiment, when applied, a near-infrared broadband light source with a bandwidth of about 100 nm is used. The light first passes through the objective lens module of the micro endoscope lens and reaches the plane glass slide. A part of the light is reflected to form a reference light, while the other part of the light passes through the plane glass slide and is reflected by the sample surface to form a sample return light. The two beams of return light interfere when they meet, and the interference light carries phase information corresponding to the optical path difference. Since a broadband light source is used, the optical path difference of the two beams of light is maintained within the coherence length range, thereby achieving low-coherence interference. The interference light is imaged on the imaging surface after passing through the first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5 and the sixth lens 6, and an optical fiber bundle coupled to the imaging surface may also be provided.

[0041] The magnification of the micro-endoscope lens suitable for label-free quantitative phase microscopy is set to 1.58 times, and the object side field of view can reach 300μm; the overall length is less than 8mm, including the thickness of the glass slide; the overall light aperture is less than 2mm, and the conventional shell thickness is 0.2mm. Therefore, the overall micro-endoscope lens suitable for label-free quantitative phase microscopy of this embodiment can be less than 2.6mm.

[0042] The image quality of the micro endoscope lens for label-free quantitative phase microscopy imaging of this embodiment is evaluated according to the design indicators and performance test requirements, including analysis of five indicators: diffuse spot size, modulation transfer function (MTF) curve, wavefront optical path difference (OPD) curve, field curvature and distortion curve.

[0043] See also Figure 3 , is a schematic diagram of the diffuse spots of light beams from three different positions of the object side, namely, the on-axis field of view, the half field of view, and the full field of view, converging on the image plane, where the black circle represents the Airy disk. The root mean square radius (RMS radius) of the diffuse spots in each field of view is close to and smaller than the Airy disk size, which is close to the diffraction limit. At the same time, the root mean square radius of the diffuse spots in each field of view is less than 2μm, which is smaller than the radius of a single fiber bundle, meeting the design requirements of the miniature objective.

[0044] See also Figure 4, is the image-side MTF curve of the embodiment, wherein DIFF LIMIT refers to the diffraction limit, T represents the meridian plane, S represents the sagittal plane, the horizontal axis Spatical frequeney (lp / mm) is the spatial frequency, and the vertical axis Contrast is the contrast. As shown in the figure, the calculation results of the MTF curves of the meridian plane and the sagittal plane of three different fields of view, namely, the on-axis field of view (On axis), the half field of view (0.5 filed), and the full field of view (Full filed) along the radial direction of the image plane, are shown, and the MTF curves under the diffraction limit are given and compared. It can be seen from the figure that the MTF curves of each field of view are all in line with the diffraction limit, and are all greater than 0.7 at 121lp / mm, which greatly meets the design indicator that the MTF value is greater than 0.5 at 121lp / mm. At the same time, according to the calculation, the lateral resolution of this micro-objective lens is about 4.35μm.

[0045] When the diffuse spot size and MTF curve meet the requirements, the performance of the micro-objective lens is further analyzed. Figure 5 The OPD curves of the light and the main light in the three fields of view of the on-axis field (On axis), half field (0.5 filed), and full field (Full field) of this embodiment are given, and the maximum scale is 1 wavelength. The two figures of each field of view represent the meridian plane and the sagittal plane respectively, and the horizontal axis is the normalized entrance pupil coordinate. Under ideal conditions, the optical path difference should be 0, that is, the curve coincides with the horizontal axis. However, due to the existence of factors such as aberrations, it is generally believed that the optical system is diffraction-limited when the optical path difference is less than half a wavelength. It can be seen from the figure that the on-axis field of view and the 0.5 field of view both meet this condition, but there is an optical path difference curve in the full field of view that is greater than half a wavelength at the edge of the pupil. It can be considered that the miniature objective lens has achieved approximate diffraction-limited performance.

[0046] Figure 6It is the field curvature and distortion curve of the embodiment. From the figure, we can analyze the three aberrations existing in this design: field curvature, astigmatism, and distortion. Field curvature is the bending of the image field. The focus of the entire field of view is not on the same plane, and the end face of the optical fiber bundle is a plane. Too much field curvature will result in the inability to see the entire image plane at the same time. Astigmatism means that the meridian plane and the sagittal plane cannot be focused on the same position at the same time, which will make the dispersion spot too large when the light beam converges on the image plane, resulting in blurred image. Distortion is caused by the difference in magnification of the field of view from the center to the edge. If the distortion is too large, the image will be distorted. The left figure is a schematic diagram of field curvature, S represents the meridian plane, T represents the sagittal plane, the vertical axis is the normalized field of view position, the horizontal axis is the axial distance between the actual image plane of each field of view and the paraxial focal plane, and the three color curves correspond to three wavelengths. Under the three wavelength conditions, the maximum field curvature of the image side is 7.1μm, and the maximum astigmatism is 21.7μm, which are 3.78μm and 2.86μm respectively when converted to the object side, which are much smaller than the axial resolution of the phase microscope system, indicating that the field curvature and astigmatism of the micro-objective lens have been effectively corrected. The right figure is a distortion diagram, and the vertical axis is the normalized field position. The maximum distortion in the figure is at the edge of the field of view, with a distortion of 0.28%, while the human eye cannot generally distinguish distortion less than 2%. Figure 5 The field curvature curve and distortion curve diagram show that the design can correct field curvature, astigmatism and distortion well.

[0047] In summary, the present invention proposes a micro endoscope lens suitable for label-free quantitative phase microscopy imaging, which adopts a lens structure of six elements and seven lenses, and the aperture of each lens is less than 2mm, which can achieve an overall outer diameter of less than 2.6mm, and meet the requirement of an overall length of less than 8mm. At the same time, by combining positive and negative lenses, spherical lenses and aspherical lenses, the root mean square radius of the diffuse spot in each field of view is less than 2μm; the MTF curves of each field of view are all in line with the diffraction limit, and are greater than 0.7 at 121lp / mm, and the lateral resolution can be obtained by theoretical calculation to be about 4.35μm; the OPD curves of each field of view basically meet the requirement that the optical path difference is less than half a wavelength; under three wavelengths, the maximum field curvature of the image side is 7.1μm, and the maximum astigmatism is 21.7μm, which are 3.78μm and 2.86μm respectively when converted to the object side, which are much smaller than the axial resolution of the phase microscopy system; the maximum distortion is 0.28%, while the human eye generally cannot distinguish distortion less than 2%. Therefore, the present invention designs a miniature endoscope head that meets the requirements.

[0048] Those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A micro endoscope head for label-free quantitative phase microscopy, characterized in that: The optical axis includes a first lens, a second lens, a third lens, a fourth lens, a fifth lens and a sixth lens in order from the object side to the image side, each lens having an object-side surface facing the object side and allowing imaging light to pass therethrough, and an image-side surface facing the image side and allowing imaging light to pass therethrough; The first lens has a positive refractive power, the second lens has a positive refractive power or a negative refractive power, the third lens has a positive refractive power, the fourth lens has a negative refractive power, the fifth lens has a positive refractive power, and the sixth lens has a negative refractive power.

2. The label-free quantitative phase microscopy microscopy micro-endoscope lens as claimed in claim 1, characterized in that: The second lens is made of special dispersion material.

3. The micro endoscope lens for label-free quantitative phase microscopy as claimed in claim 2, characterized in that: The second lens is a biconvex lens.

4. The micro endoscope lens for label-free quantitative phase microscopy as claimed in claim 3, characterized in that: The image-side surface and the object-side surface of the second lens are both aspherical surfaces.

5. The micro endoscope lens for label-free quantitative phase microscopy as claimed in claim 1, characterized in that: The third lens and the fourth lens are double-cemented lenses, which are made of a combination of a strong dispersion material and a weak dispersion material.

6. The micro endoscope lens for label-free quantitative phase microscopy as claimed in claim 5, characterized in that: The first lens is a crescent lens, the third lens is a double convex lens, and the object side surface and the image side surface of the fourth lens are concave surfaces.

7. The label-free quantitative phase microscopy microscopy micro-endoscope lens as claimed in claim 1, characterized in that: The fifth lens is a biconvex lens, and the object side surface of the fifth lens is an aspherical surface.

8. The label-free quantitative phase microscopy microscopy micro-endoscope lens as claimed in claim 1, characterized in that: The sixth lens is a biconcave lens.

9. The label-free quantitative phase microscopy microscopy micro-endoscope lens as claimed in claim 1, characterized in that: The refractive index of the material used for the sixth lens is similar to that of the fifth lens, but the dispersion coefficient is different.

10. The micro endoscope lens for label-free quantitative phase microscopy according to any one of claims 1 to 9, characterized in that: There is also a lens without refractive power on the optical axis between the object side and the first lens for generating system interference.

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