A low-distortion achromatic lens and a wide-spectrum segmented spectral detection device

Abstract

The present invention relates to the field of spectral detection technology, and specifically provides a low-distortion achromatic lens and a wide-spectrum segmented spectral detection device. The lens includes a front lens group, an intermediate lens group, and a rear lens group. The front lens group includes a first lens with positive optical power and a second lens with negative optical power. The intermediate lens group includes a third lens and a fifth lens with positive optical power, and a fourth lens with negative optical power. The rear lens group includes a sixth lens with positive optical power and a seventh lens with negative optical power. By optimizing and adjusting the optical parameters of each lens, the aberration and chromatic dispersion are effectively reduced, and extremely low distortion is achieved within a wide spectrum and a large field of view. Applying this kind of lens to a wide-spectrum segmented spectral detection device can achieve high-sampling-rate accurate detection of near-infrared continuous wide-spectrum, meeting the requirements for improving the axial resolution and axial vector range of the spectral optical coherence tomography system.

Description

Technical Field

[0001] The present invention belongs to the technical field of spectral detection, and in particular relates to a low-distortion achromatic lens and a wide-spectrum segmented spectral detection device. Background Technique

[0002] Optical coherence tomography technology is a tomographic imaging technology based on low-coherence light interference. Compared with other non-contact non-destructive tomographic technologies such as X-ray tomography and ultrasonic tomography, optical coherence tomography technology has significant advantages of being radiation-free and having high resolution.

[0003] Currently, optical coherence tomography technology has been maturely applied in the fields of biomedicine and industrial inspection. Among them, the more widely used one is spectral-domain optical coherence tomography technology. Both this technology and the early-developed time-domain optical coherence tomography technology are based on the principle of low-coherence light interference to realize the analysis of tomographic information. The difference lies in the detection and processing methods of the interference signals for the two: time-domain optical coherence tomography technology uses a single-point photodetector to receive the interference light field that changes with time, and obtains tomographic structure information by analyzing the intensity change situation of the interference light field within a specific time period; spectral-domain optical coherence tomography technology uses a spectrometer to collect instantaneous interference spectra and obtains tomographic structure information by analyzing the interference spectral data. Relatively speaking, the latter has a higher working frequency and sensitivity.

[0004] Figure 1 Shown is a schematic structural diagram of a typical Michelson interferometric spectral-domain optical coherence tomography system. The light wave emitted by the broadband light source is divided into two beams by a beam splitter. One beam propagates to reach the mirror and returns along the original path to form the reference arm optical path, and the other beam propagates to irradiate the sample to be measured. The backward scattered light field at the sample returns along the original path to form the sample arm optical path. The light waves returned by the reference arm and the sample arm interfere again at the beam splitter. By performing an inverse Fourier transform on the interference spectrum collected by the spectrometer, the structural information in the depth direction of the sampling position of the sample to be measured can be obtained at one time.

[0005] In practical applications, since light waves in the near-infrared spectral band (about 750nm - 1500nm) show good transmissibility for most substances, the working band of most optical coherence tomography systems is selected in the near-infrared spectral band. The ideal axial resolution of the system is:

[0006] (1.1)

[0007] where is the central wavelength of the working band, is the working band width.

[0008] For a spectral-domain optical coherence tomography system, the axial range of the system is:

[0009] (1.2)

[0010] wherein is the spectral sampling rate of the spectrometer, which is determined by the ratio of the working band width to the number of sampling pixels and is determined accordingly.

[0011] As can be seen from Formula (1.1) and Formula (1.2), when the central wavelength of the working band of the spectral domain optical coherence tomography system is determined, in order to improve the axial resolution and axial range of the system, it is necessary for the spectral detection device, which is one of the core components of the system, to have a wider continuous spectral band detection ability and a higher spectral sampling rate. The wider the continuous spectral band to be detected, the higher the requirements for the focusing lens group in the spectral detection device, which is mainly manifested as the aberration balance and chromatic aberration constraint in a wide field of view. At the same time, since the spectral domain optical coherence tomography system extracts tomographic information by solving the interference spectrum, in order to reduce the pressure of "spectral calibration" in the data processing process, it is required that the imaging distortion of the focusing lens group should be as small as possible. The reflection system itself has no chromatic aberration, and the design pressure for the above requirements is relatively small, but the processing cost and the alignment difficulty are relatively high; in contrast, the transmissive system formed by stacking traditional spherical lenses is still the currently preferred solution.

[0012] In terms of dispersive spectral sampling, the use of a one-dimensional linear array photodetector can achieve it. However, due to the manufacturing process limitations and the requirements for product yield, it is not easy to manufacture a long target surface and multi-pixel linear array detector required for wide-spectrum high-sampling-rate detection, and the cost is high. More importantly, there is currently no mature high-quantum efficiency photodetector that can be used for near-infrared full-spectrum detection. As Figure 2 shown, conventional silicon-based detectors can basically only cover the near-infrared spectral detection in the range of 780nm - 1000nm, while the spectral response of InGaAs detectors usually starts at about 900nm and cannot be used for near-infrared spectral detection below 900nm.

[0013] The above problems restrict the design and development of spectrometers for improving the axial resolution and axial range of spectral domain optical coherence tomography systems. Therefore, there is an urgent need for a transmissive low-distortion achromatic lens and a segmented spectral detection device suitable for near-infrared continuous wide-spectrum detection. Summary of the Invention

[0014] In view of this, the present invention aims to provide a low-distortion achromatic lens and a wide-spectrum segmented spectral detection device for a spectral domain optical coherence tomography system, so as to achieve high-sampling-rate accurate detection of near-infrared continuous wide-spectrum, and meet the requirements for improving the axial resolution and axial range of the spectral domain optical coherence tomography system.

[0015] To achieve the above object, the technical solution of the present invention is realized as follows:

[0016] On the one hand, the present invention provides a low-distortion achromatic lens, including, arranged in sequence along the optical axis: a front lens group, an intermediate lens group, and a rear lens group;

[0017] Among them, the front lens group includes, arranged in sequence along the optical axis: a first lens and a second lens, the first lens having a positive optical power; the second lens having a negative optical power;

[0018] The intermediate lens group includes, arranged in sequence along the optical axis: a third lens, a fourth lens, and a fifth lens, both the third lens and the fifth lens having a positive optical power; the fourth lens having a negative optical power;

[0019] The rear lens group includes, arranged in sequence along the optical axis: a sixth lens and a seventh lens, the sixth lens having a positive optical power; the seventh lens having a negative optical power;

[0020] The refractive index range of the first lens is 1.56 - 1.58;

[0021] The refractive index range of the second lens is 1.48 - 1.50;

[0022] The refractive index ranges of the third lens, the fifth lens, and the sixth lens are all 1.74 - 1.76;

[0023] The refractive index range of the fourth lens is 1.95 - 1.97;

[0024] The refractive index range of the seventh lens is 1.58 - 1.60.

[0025] Preferably, the first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are all spherical lenses;

[0026] The focal length of the front lens group Satisfies: , the focal length of the intermediate lens group Satisfies: , the focal length of the rear lens group Satisfies: , where Is the total focal length of the low-distortion achromatic lens.

[0027] Preferably, the radius of curvature of the front surface of the first lens Satisfies: , the radius of curvature of the rear surface Satisfies: ;

[0028] The radius of curvature of the front surface of the second lens Satisfies: , the radius of curvature of the rear surface satisfies: ;

[0029] The radius of curvature of the front surface of the third lens satisfies: , the radius of curvature of the rear surface satisfies: ;

[0030] The radius of curvature of the front surface of the fourth lens satisfies: , the radius of curvature of the rear surface satisfies: ;

[0031] The radius of curvature of the front surface of the fifth lens satisfies: , the radius of curvature of the rear surface satisfies: ;

[0032] The radius of curvature of the front surface of the sixth lens satisfies: , the radius of curvature of the rear surface satisfies: ;

[0033] The radius of curvature of the front surface of the seventh lens satisfies: , the radius of curvature of the rear surface satisfies: , where is the total focal length of the low-distortion achromatic lens.

[0034] Preferably, the Abbe number range of the first lens is 69 - 73;

[0035] The Abbe number range of the second lens is 69 - 73;

[0036] The Abbe number ranges of the third lens, the fifth lens, and the sixth lens are all 43 - 47;

[0037] The Abbe number range of the fourth lens is 15 - 19;

[0038] The Abbe number range of the seventh lens is 59 - 63.

[0039] Preferably, the total focal length of the low-distortion achromatic lens is mm.

[0040] Preferably, the working spectral range is 700nm - 1500nm, the entrance pupil size ≤ 25mm, and the distance from the entrance pupil plane to the projection of the front surface of the first lens on the optical axis ≤100 mm.

[0041] Preferably, the projection distance of the air gap between the first lens and the second lens on the optical axis is mm;

[0042] The projection distances of the air gaps between the third lens and the fourth lens and between the fourth lens and the fifth lens on the optical axis are both mm;

[0043] The projection distance of the air gap between the sixth lens and the seventh lens on the optical axis is mm;

[0044] The projection distance of the air gap between the rear surface of the second lens and the front surface of the third lens on the optical axis is mm;

[0045] The projection distance of the air gap between the rear surface of the fifth lens and the front surface of the sixth lens on the optical axis is mm.

[0046] On the other hand, the present invention provides a broadband segmented spectroscopic detection device, comprising: a dispersion element, a beam splitting element, and at least two detection branches;

[0047] Wherein, the dispersion element is used to separate lights with different wavelengths in the beam to be detected and irradiate them on the beam splitting element at different angles; the beam splitting element splits the beam to be detected into sub-beams with multiple different wavelength ranges and transmits each sub-beam to different detection branches respectively;

[0048] Each detection branch includes a low-distortion achromatic lens and a detector; the low-distortion achromatic lens is used to focus the incident sub-beam onto the photosensitive surface of the detector.

[0049] Preferably, it further includes a conducting optical fiber and a collimator arranged on the optical path in front of the dispersion element, and a data processing system connected to each detector; the conducting optical fiber is used to transmit the beam to be detected and irradiate the beam to be detected on the collimator, and the collimator collimates the beam to be detected into a parallel beam and irradiates it on the dispersion element;

[0050] The data processing system is used to fuse the imaging information of each detector to achieve continuous broadband spectroscopic detection.

[0051] Preferably, it includes: a first detection branch and a second detection branch. The first detection branch includes a first low-distortion achromatic lens and a first detector; the second detection branch includes a second low-distortion achromatic lens and a second detector;

[0052] The beam splitting element is a dichroic beam splitter, and for the beam to be detected, the wavelength range is to The sub-beams have a transmission effect on the wavelength range of to The sub-beams have a reflection effect. to The sub-beams are focused on the photosensitive surface of the first detector through the first low-distortion achromatic lens; to The sub-beams are focused on the photosensitive surface of the second detector through the second low-distortion achromatic lens.

[0053] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0054] The lens provided by the present invention combines optical lenses with different refractive indices and different Abbe number dispersion characteristics, so that the lens can effectively constrain the chromatic aberration in the wide spectral range of 700nm - 1500nm under the conditions of a maximum entrance pupil size of 25mm, a maximum entrance pupil distance of 100mm, and a maximum field of view angle of ±7.5°. And through the optimized design of the optical parameters such as the curvature radius, optical thickness, and air gap of each lens in the lens, the lens can achieve good aberration balance under wide-spectrum and large-field conditions. At the same time, through the linkage adjustment of the front lens group, the middle lens group, and the rear lens group, the relative distortion amount within the full field of view of the lens can be controlled within an extremely low range of less than 0.02%, reducing the pressure of "spectral calibration" in the data processing process of the spectral detection system and improving the overall performance and imaging accuracy of the spectral domain optical coherence tomography system.

[0055] In addition, this kind of lens is only composed of seven lenses, involving fewer lenses and each lens is a spherical lens, which is convenient for processing. Moreover, the relatively compact distribution of the front, middle, and rear groups of lenses is more conducive to alignment and adjustment, reducing the manufacturing cost and difficulty, and is very suitable for large-scale mass production.

[0056] Furthermore, although this kind of lens is designed for the wide-spectrum dispersion spectral focusing function, it can also be used as a conventional imaging lens. Due to its excellent optical performance, it also has extremely high application value in the fields of near-infrared optical observation, near-infrared vision detection, etc. Based on the optical structure of this kind of lens, targeted scaling adjustment or even flexible zoom structure improvement can be carried out to meet the needs of different application scenarios.

[0057] The wide-spectrum segmented spectrum detection device provided by the present invention can be applied to the spectrum domain optical coherence tomography system. By utilizing the coordination of the dispersion element and the spectroscopic element, the near-infrared spectrum to be detected is separated into two spectrum segments, the transmission and reflection spectrum segments. Two detectors are then used to detect the two spectrum segments separately. Finally, the data processing system is used to analyze and fuse them. Through the segmented detection method, high sampling rate and accurate detection of the near-infrared continuous wide spectrum segment can be achieved. And on this basis, the sampling pixel number expansion scheme can be implemented in combination with the spectrum ranges that the two photoelectric detectors each deal with, which can further improve the spectrum sampling rate.

[0058] The present invention adopts a pre-splitting strategy, and a low-distortion achromatic lens with focusing function is separately set in each detection branch, and a splitter element is inserted in the overlapping area of ​​multi-color light waves behind the dispersion element to directly separate the spectrum, and the full spectrum to be detected is divided into multiple spectrum ranges, and each spectrum beam is detected separately, which effectively reduces the off-axis aberration correction pressure of the focusing lens. In general, the full spectrum can be divided into a transmission spectrum and a reflection spectrum, which can effectively reduce the aberration correction pressure and ensure high-quality detection of the full spectrum. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The drawings constituting part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation on the present invention. In the drawings:

[0060] Figure 1 It is a schematic structural diagram of a conventional Michelson interferometric spectral domain optical coherence tomography system in the background art;

[0061] Figure 2 It is a spectral response curve diagram of a silicon-based detector and an InGaAs detector in the background technology;

[0062] Figure 3 is a schematic structural diagram of a low-distortion achromatic lens according to an embodiment of the present invention;

[0063] Figure 4 Schematic diagram of the simulation of the light wave convergence points in different fields and spectrum bands of the focal plane of the low distortion achromatic lens provided by the embodiment of the present invention

[0064] Figure 5 is a schematic diagram of simulation of focal plane magnification chromatic aberration of a low-distortion achromatic lens provided according to an embodiment of the present invention;

[0065] Figure 6 is a schematic diagram of axial chromatic aberration distribution simulation of a low-distortion achromatic lens provided according to an embodiment of the present invention;

[0066] Figure 7It is a schematic diagram of the field curvature simulation of the low-distortion achromatic lens provided by an embodiment of the present invention;

[0067] Figure 8 It is a schematic diagram of the relative distortion simulation of the low-distortion achromatic lens provided by an embodiment of the present invention;

[0068] Figure 9 It is a schematic diagram of the composite MTF curve simulation of the low-distortion achromatic lens provided by an embodiment of the present invention;

[0069] Figure 10 It is a schematic diagram of the structure of the wide-spectrum segmented spectral detection device provided by an embodiment of the present invention;

[0070] Figure 11 It is a schematic diagram of the optical path of the wide-spectrum segmented spectral detection device provided by an embodiment of the present invention;

[0071] Figure 12 It is a schematic diagram of the focusing effect simulation of the detector target surface of the wide-spectrum segmented spectral detection device for light waves of different wavelengths.

[0072] The reference numerals therein include:

[0073] The first lens 1, the second lens 2, the third lens 3, the fourth lens 4, the fifth lens 5, the sixth lens 6, the seventh lens 7, the entrance pupil surface 8, the focal plane 9;

[0074] The conductive optical fiber 100, the collimator 200, the dispersion element 300, the beam splitting element 400, the first low-distortion achromatic lens 501, the second low-distortion achromatic lens 502, the first detector 601, the second detector 602, the data processing system 700. Detailed implementation manners

[0075] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates on the present invention in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation to the present invention. Similar elements in different embodiments are labeled with related similar element numbers. In the following embodiments, many detailed descriptions are provided to enable a better understanding of the present invention. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, or methods. In some cases, some operations related to the present invention are not shown or described in the specification to avoid inundating the core part of the present invention with excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail, and they can fully understand the related operations based on the descriptions in the specification and the general technical knowledge in the art.

[0076] It should be noted that, without conflict, the embodiments and the features in the embodiments of the present invention can be combined with each other to form various embodiments. At the same time, the steps or actions in the method description can also be adjusted in the order that is obvious to those skilled in the art. Therefore, the various orders in the specification and the drawings are only for clearly describing a certain embodiment and do not mean that they are the necessary orders, unless it is stated that a certain order must be followed.

[0077] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise stated, the meaning of "a plurality" is two or more.

[0078] In the description of the present invention, it should be noted that unless otherwise clearly defined and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0079] The present invention will be described in detail below with reference to the drawings and in conjunction with embodiments.

[0080] Please refer to Figure 1 , in an embodiment of the present invention, a low-distortion achromatic lens is provided, which is mainly applied to the 700nm - 1500nm near-infrared spectrum detection, and is used to solve the problems of insufficient aberration and chromatic aberration correction ability and serious imaging distortion of existing focusing lenses under the conditions of large field of view and wide spectrum application. Specifically, the lens includes: a front lens group, an intermediate lens group, and a rear lens group arranged in sequence along the incident light optical axis direction from the entrance pupil surface 8. Among them, the front lens group includes a first lens 1 and a second lens 2 arranged in sequence along the incident light optical axis direction. The first lens 1 is a positive refractive power spherical lens, and its optional refractive index range is 1.56 - 1.58, and the Abbe number range is 69 - 73. In the embodiment of the present invention, the refractive index of the first lens 1 is specifically 1.5691. The preparation material of the first lens 1 is H-ZPK7 glass, and its Abbe number is 71.30. Along the incident optical axis direction, the curvature radius satisfies: , and the curvature radius of the rear surface (i.e., the mirror surface far from the entrance pupil surface 8) satisfies: , where is the total focal length of the low-distortion achromatic lens. In the embodiment of the present invention, the curvature radius of the front surface of the first lens 1 is selected as , and the curvature radius of the rear surface of the first lens 1 is selected as . In addition, the size of the entrance pupil surface 8 is less than or equal to 25mm, and the projection distance of the air gap between the entrance pupil surface 8 and the front surface of the first lens 1 on the optical axis is ≤ 100mm.

[0081] The second lens 2 is a negative meniscus lens, and its optional refractive index ranges from 1.48 to 1.50, and the Abbe number ranges from 69 to 73. In the embodiment of the present invention, the refractive index of the second lens 2 is specifically 1.4875. The preparation material of the second lens 2 is H-QK3L glass, and its Abbe number is 70.44. Along the incident optical axis direction, the curvature radius of the front surface of the second lens 2 satisfies: , and the curvature radius of the rear surface satisfies: . In the embodiment of the present invention, the curvature radius of the front surface of the second lens 2 is selected as , and the curvature radius of the rear surface of the second lens 2 is selected as .

[0082] By designing the central thickness of the first lens 1, the central thickness of the second lens 2, and the projection distance of the air gap between the two on the optical axis , the equivalent focal length of the front lens group as a whole satisfies: . Among them, the central thickness of the first lens 1 mm, the central thickness of the second lens 2 mm, and the projection distance of the air gap between the first lens 1 and the second lens 2 on the optical axis mm.

[0083] The middle lens group includes a third lens 3, a fourth lens 4, and a fifth lens 5 arranged in sequence along the incident optical axis direction. The third lens 3 is a positive meniscus lens, and its optional refractive index ranges from 1.74 to 1.76, and the Abbe number ranges from 43 to 47. In the embodiment of the present invention, the refractive index of the third lens 3 is specifically 1.7440. The preparation material of the third lens 3 is H-LAF3B glass, and its Abbe number is 44.90. Along the incident optical axis direction, the curvature radius of the front surface of the third lens 3 satisfies: , and the curvature radius of the rear surface satisfies: . In the embodiment of the present invention, the curvature radius of the front surface of the third lens 3 is selected as , and the curvature radius of the rear surface of the third lens 3 is selected as .

[0084] The fourth lens 4 is a spherical lens with negative optical power. The optional refractive index range is 1.95 to 1.97, and the Abbe number range is 15 to 19. In the embodiment of the present invention, the refractive index of the fourth lens 4 is specifically 1.9591. The preparation material of the fourth lens 4 is H-ZF73 glass, and its Abbe number is 17.47. Along the incident optical axis direction, the curvature radius of the front surface of the fourth lens 4 satisfies: , and the curvature radius of the rear surface satisfies: . In the embodiment of the present invention, the curvature radius of the front surface of the fourth lens 4 is selected as , and the curvature radius of the rear surface of the fourth lens 4 is selected as .

[0085] The fifth lens 5 is a spherical lens with positive optical power. The optional refractive index range is 1.74 to 1.76, and the Abbe number range is 43 to 47. In the embodiment of the present invention, the refractive index of the fifth lens 5 is specifically 1.7440. The preparation material of the third lens 3 is H-LAF3B glass, and its Abbe number is 44.90. Along the incident optical axis direction, the curvature radius of the front surface of the fifth lens 5 satisfies: , and the curvature radius of the rear surface satisfies: . In the embodiment of the present invention, the curvature radius of the front surface of the fifth lens 5 is selected as , and the curvature radius of the rear surface of the fifth lens 5 is selected as .

[0086] By designing the central thickness of the third lens 3 , the central thickness of the fourth lens 4 , the central thickness of the fifth lens 5 , and the projection distance of the air gaps between the three on the optical axis, the equivalent focal length of the overall intermediate lens group satisfies: . Among them, the central thickness of the third lens 3 mm, the central thickness of the fourth lens 4 mm, the central thickness of the fifth lens 5 mm. The projection distance of the air gap between the front surface of the third lens 3 and the rear surface of the second lens 2 on the optical axis mm. The projection distance of the air gap between the rear surface of the third lens 3 and the front surface of the fourth lens 4 on the optical axis mm. The projection distance of the air gap between the rear surface of the fourth lens 4 and the front surface of the fifth lens 5 on the optical axis mm.

[0087] The rear lens group includes a sixth lens 6 and a seventh lens 7 arranged in sequence along the optical axis of the incident light. The sixth lens 6 is a spherical lens with a positive optical power, and its optional refractive index range is 1.74 to 1.76, and the Abbe number range is 43 to 47. In an embodiment of the present invention, the refractive index of the sixth lens 6 is specifically 1.7440. The preparation material of the sixth lens 6 is H-LAF3B glass, and its Abbe number is 44.90. Along the optical axis of the incident light, the radius of curvature of the front surface of the sixth lens 6 satisfies: , and the radius of curvature of the rear surface satisfies: . In an embodiment of the present invention, the radius of curvature of the front surface of the sixth lens 6 is selected as , and the radius of curvature of the rear surface of the sixth lens 6 is selected as . In addition, the projection distance of the air gap between the front surface of the sixth lens 6 and the rear surface of the fifth lens 5 on the optical axis mm.

[0088] The seventh lens 7 is a spherical lens with a negative optical power, and its optional refractive index range is 1.58 to 1.60, and the Abbe number range is 59 to 63. In an embodiment of the present invention, the refractive index of the seventh lens 7 is specifically 1.5891. The preparation material of the seventh lens 7 is H-ZK3 glass, and its Abbe number is 61.25. Along the optical axis of the incident light, the radius of curvature of the front surface of the seventh lens 7 satisfies: , and the radius of curvature of the rear surface satisfies: . In an embodiment of the present invention, the radius of curvature of the front surface of the seventh lens 7 is selected as , and the radius of curvature of the rear surface of the seventh lens 7 is selected as .

[0089] By designing the central thickness of the sixth lens 6, the central thickness of the seventh lens 7, and the projection distance of the air gap between the two on the optical axis, the equivalent focal length of the entire rear lens group is made to satisfy: . Among them, the central thickness of the sixth lens 6 is mm, the central thickness of the seventh lens 7 is

[0090] Based on the above optical structure and parameter design, in the embodiments of the present invention, a simulation software is used to simulate the low-distortion achromatic lens. Through simulation experiments, the imaging results on the focal plane of the lens as shown in Figure 4 are obtained. In the range of a half field of view of 7.5°, the RMS radius values of the dispersion spots formed by the focusing of light waves with different wavelengths in the spectral range from 700 nm to 1500 nm are all less than 4 μm, and are within the diffraction limit range corresponding to the central wavelength of 1100 nm in the spectral range of 700 nm - 1500 nm (the circle formed by the black solid lines in the figure, with a radius of 5.37 μm).

[0091] As shown in Figure 5 , in the range of a half field of view of 7.5°, the change amount of the lateral chromatic aberration of light waves with different wavelengths in the spectral range from 700 nm to 1500 nm is less than the diffraction limit range corresponding to the central wavelength of 1100 nm ( Figure 5 the range shown by the two dashed lines in the figure).

[0092] As shown in Figure 6 , in the range of a 25 mm-sized pupil, the distribution range of the axial chromatic focal shift between light waves with different wavelengths in the spectral range from 700 nm to 1500 nm on each aperture band is less than 30 μm, which is within the system focal depth range, and the theoretically calculated value of the system focal depth is 70 μm.

[0093] As shown in Figure 7 , in the range of a half field of view of 7.5° of the low-distortion achromatic lens, the maximum field curvature is less than 0.05 mm.

[0094] As shown in Figure 8 , the maximum relative distortion of the low-distortion achromatic lens is less than 0.02%

[0095] As shown in Figure 9 , in the range of a half field of view of 7.5° of the low-distortion achromatic lens, the chromatic MTF curves of each field of view are all close to the diffraction limit.

[0096] Based on the above simulation verification results, it can be obtained that: under the conditions of a maximum entrance pupil size of 25 mm, a maximum entrance pupil distance of 100 mm, and a maximum field of view angle of ±7.5° of the low-distortion achromatic lens in the embodiments of the present invention, it shows good aberration balance ability, and can achieve good chromatic aberration control for light waves in the wide spectral range of 700 nm - 1500 nm. At the same time, the imaging distortion amount is extremely low.

[0097] As shown in Figure 10 and 11As shown, in an embodiment of the present invention, a wide-spectrum segmented spectral detection device applicable to a spectral domain optical coherence tomography system is further provided to meet the requirements for improving the axial resolution and axial range of the spectral domain optical coherence tomography system. This device will use the above-mentioned low-distortion achromatic lens or a scaled lens based on it for beam focusing. Specifically, the wide-spectrum segmented spectral detection device includes: a conducting optical fiber 100, a collimator 200, a dispersion element 300, a beam-splitting element 400, a first low-distortion achromatic lens 501, a second low-distortion achromatic lens 502, a first detector 601, a second detector 602, and a data processing system 700. Among them, the conducting optical fiber 100 is a low-dispersion single-mode optical fiber, which is arranged at the forefront of the optical path. Its main function is to transmit the interference beam to be detected in the spectral domain optical coherence tomography system to the wide-spectrum segmented spectral detection device. A collimator 200 is arranged on the light-emitting optical path of the conducting optical fiber 100. The collimator 200 can be selected as a transmissive optical element or a reflective optical element, and it is used to collimate and correct chromatic aberration for the beam to be detected emitted from the conducting optical fiber 100. The light-emitting port of the conducting optical fiber 100 is located on the focal plane of the collimator 200. The polychromatic beam to be detected in the spectral range of 760 nm - 1100 nm is incident on the collimator 200 from the light-emitting port of the conducting optical fiber 100 at a certain aperture angle. The collimator 200 processes the beam to be detected into a parallel beam, and the parallel beam continues to be incident on the dispersion element 300 at a specific angle. In an embodiment of the present invention, the dispersion element 300 can be selected as a diffraction grating or a dispersion prism. Through the dispersion element 300, the light waves of different wavelengths in the beam to be detected are emitted at different diffraction angles, realizing the separation of light of different wavelengths. The light of different wavelengths is incident on the beam-splitting element 400 at a divergent separation angle. The beam-splitting element 400 is used to split the beam to be detected, forming multiple sub-beams in different wavelength ranges. Each sub-beam is incident on a different detection branch, and the multiple sub-beams in different wavelength ranges are detected segmentally through different detection branches to solve the problem that the working spectral range of the current detector is relatively narrow and cannot cover wide-spectrum detection.

[0098] In an embodiment of the present invention, the beam-splitting element 400 adopts a dichroic beam splitter, allowing light waves in the wavelength range to be transmitted, and light waves in the wavelength range to be reflected, and the light waves in are incident on the first low-distortion achromatic lens 501, and the first low-distortion achromatic lens 501 focuses them on the target surface of the first detector 601. The light waves in

[0099] In the embodiments of the present invention, the detection is mainly directed to the polychromatic light waves in the range of 760 nm - 1100 nm. Therefore, the transmission and reflection of different spectral bands are regulated through different surface film layers. Under the action of the optical thin film on the dichroic beam splitter, the light waves in the spectral band of 760 nm - 930 nm are reflected and enter the first low-distortion apochromatic lens 501, and are detected on the target surface of the first detector 601. The light waves in the spectral band of 930 nm - 1100 nm are transmitted and enter the second low-distortion apochromatic lens 502, and are detected on the target surface of the second detector 602. Among them, both the first detector 601 and the second detector 602 are linear array detectors, and can be selected according to the corresponding detection band range. In the embodiments of the present invention, the first detector 601 is selected as a silicon-based detector, and the second detector 602 is selected as an InGaAs detector. After the silicon-based detector and the InGaAs detector detect the light waves in the spectral bands of 760 nm - 930 nm and 930 nm - 1100 nm respectively, the spectral information is fused by the data processing system 700 connected to both of them, realizing the detection of a continuous wide spectral band of near-infrared light.

[0100] As Figure 12 shown, the focused spots of each wavelength in the spectral band of 760 nm - 930 nm and the spectral band of 930 nm - 1100 nm are evenly distributed on the target surfaces of the first detector 601 and the second detector 602, and their respective distribution ranges basically completely cover the target surfaces of the corresponding detectors. Sampling can be carried out on the first detector 601 and the second detector 602 at a wavelength interval of 0.085 nm.

[0101] For the specific parameters of the wide spectral range segmented spectral detection device in this embodiment, please refer to the following table:

[0102] Table 1 Parameters of the Wide Spectral Range Segmented Spectral Detection Device

[0103]

[0104] The wide spectral range segmented spectral detection device in the embodiments of the present invention combines the spectral response characteristics of silicon-based detectors and InGaAs detectors, realizes wide spectral response through segmented detection, solves the problem of limited detection spectral bands in current spectral domain optical coherence tomography systems, and more segments can be made on the basis of the present invention according to actual needs, and precise detection can be carried out on each segment to meet the actual application requirements. Segmented detection can not only improve the detection accuracy, but also reduce the off-axis aberration correction pressure of the focusing lens during the imaging focusing process.

[0105] In summary, the above description is only the preferred embodiments of this specification and is not used to limit the protection scope of this specification. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of this specification shall be included within the protection scope of this specification.

[0106] The systems, devices, modules or units described in one or more of the above embodiments may be specifically implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop computer, a cellular phone, a camera phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or any combination of these devices.

[0107] It should also be noted that the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, commodity or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such process, method, commodity or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, commodity or device comprising the element.

[0108] Each embodiment in this specification is described in a progressive manner. The same or similar parts among the embodiments can be referred to each other, and the key point of each embodiment is to illustrate the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method embodiment.

[0109] The above describes specific embodiments of this specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve the desired result. Additionally, the processes depicted in the figures do not necessarily require the particular order or sequential order shown to achieve the desired result. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

Claims

1. An achromatic lens with low distortion, characterized in that, Including, arranged in sequence along the optical axis direction: a front lens group, an intermediate lens group, and a rear lens group; Wherein, the front lens group includes, arranged in sequence along the optical axis direction: a first lens and a second lens, the first lens having a positive optical power; the second lens having a negative optical power; The intermediate lens group includes, arranged in sequence along the optical axis direction: a third lens, a fourth lens, and a fifth lens, the third lens and the fifth lens both having positive optical powers; the fourth lens having a negative optical power; The rear lens group includes, arranged in sequence along the optical axis direction: a sixth lens and a seventh lens, the sixth lens having a positive optical power; the seventh lens having a negative optical power; The refractive index range of the first lens is 1.56 to 1.58; The refractive index range of the second lens is 1.48 to 1.50; The refractive index ranges of the third lens, the fifth lens, and the sixth lens are all 1.74 to 1.76; The refractive index range of the fourth lens is 1.95 to 1.97; The refractive index range of the seventh lens is 1.58 to 1.60; The focal length of the front lens group satisfies: , the focal length of the intermediate lens group satisfies: , the focal length of the rear lens group satisfies: , where is the total focal length of the low-distortion achromatic lens.

2. The apochromatic lens with low distortion according to claim 1, characterized in that The first lens, the second lens, the third lens, the fourth lens, the fifth lens, the sixth lens, and the seventh lens are all spherical lenses; The radius of curvature of the front surface of the first lens satisfies: , and the radius of curvature of the rear surface satisfies: ; The radius of curvature of the front surface of the second lens satisfies: , and the radius of curvature of the rear surface satisfies: ; The radius of curvature of the front surface of the third lens satisfies: , and the radius of curvature of the rear surface satisfies: ; The radius of curvature of the front surface of the fourth lens satisfies: , and the radius of curvature of the rear surface satisfies: ; The radius of curvature of the front surface of the fifth lens satisfies: , and the radius of curvature of the rear surface satisfies: ; The radius of curvature of the front surface of the sixth lens satisfies: , and the radius of curvature of the rear surface satisfies: ; The radius of curvature of the front surface of the seventh lens satisfies: , and the radius of curvature of the rear surface satisfies: , where is the total focal length of the low-distortion achromatic lens.

3. The low-distortion achromatic lens according to claim 1, characterized in that, The Abbe number range of the first lens is 69 to 73; The Abbe number range of the second lens is 69 to 73; The Abbe number ranges of the third lens, the fifth lens, and the sixth lens are all 43 to 47; The Abbe number range of the fourth lens is 15 to 19; The Abbe number range of the seventh lens is 59 to 63.

4. The low-distortion achromatic lens according to any one of claims 1 to 3, characterized in that The total focal length of the low-distortion achromatic lens is mm.

5. The apochromatic lens with low distortion according to claim 4, characterized in that, The working spectral range is 700nm - 1500nm, the entrance pupil size ≤ 25mm, and the distance between the entrance pupil plane and the projection of the front surface of the first lens on the optical axis ≤ 100mm.

6. The apochromatic lens with low distortion according to claim 2, characterized in that, The projection distance of the air gap between the first lens and the second lens on the optical axis is mm; The projected distances on the optical axis of the air spaces between the third lens and the fourth lens and between the fourth lens and the fifth lens are both mm; The projection distance of the air gap between the sixth lens and the seventh lens on the optical axis is mm; The projection distance on the optical axis of the air gap between the rear surface of the second lens and the front surface of the third lens is mm; The projection distance on the optical axis of the air gap between the rear surface of the fifth lens and the front surface of the sixth lens is mm.

7. A broadband segmented spectral detection device, characterized in that Including: A dispersion element, a beam splitting element, and at least two detection branches; Wherein, the dispersion element is used to separate lights of different wavelengths in the beam to be detected and project them onto the beam splitting element at different angles; the beam splitting element splits the beam to be detected into sub-beams with multiple different wavelength ranges and transmits each sub-beam to different ones of the detection branches; Each of the detection branches includes a low-distortion achromatic lens and a detector as described in any one of claims 1 to 6; the low-distortion achromatic lens is used to focus the incident sub-beam onto the photosensitive surface of the detector.

8. The broadband segmented spectroscopic detection device according to claim 7, characterized in that, It further includes a conducting optical fiber and a collimator arranged on the optical path in front of the dispersion element, and a data processing system connected to each detector; the conducting optical fiber is used to transmit the beam to be detected and project the beam to be detected onto the collimator, and the collimator collimates the beam to be detected into a parallel beam and projects it onto the dispersion element; The data processing system is used to fuse the imaging information of each detector to achieve continuous wide-spectrum spectral detection.

9. The broadband segmented spectral detection device according to claim 7, wherein Including: A first detection branch and a second detection branch. The first detection branch includes a first low-distortion achromatic lens and a first detector; the second detection branch includes a second low-distortion achromatic lens and a second detector; The beam splitting element is a dichroic beam splitter, which has a transmission effect on the sub-beams with wavelengths in the range of to in the to-be-detected beam, and has a reflection effect on the sub-beams with wavelengths in the range of to ; the sub-beams with wavelengths in the range of to are focused on the photosensitive surface of the first detector through the first low-distortion achromatic lens; to the sub-beams are focused on the photosensitive surface of the second detector through the second low-distortion achromatic lens.

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