Spectrometer for optical coherence tomography

Abstract

The invention relates to the field of optics, in particular to a spectrometer for optical coherence tomography, which sequentially comprises a collimation unit, a grating light splitting element, a reflector, a focusing unit and a linear array camera according to a light line, the collimation unit optimizes the distance between lenses and a light source and the air interval between the two lenses, so that the incident angle and the emergent angle of light in the collimation unit are in smooth transition. The grating light splitting element adopts a height logarithm design to realize separation of optical signals of different wavebands, and the focal length requirement of a subsequent focusing system is reduced; the reflector folds back the light path, so that the collimation end and the detection part are arranged in parallel, and the overall length of the system is effectively shortened by folding the light path; the focusing unit distributes positive and negative focal power of each element and inhibits aberration of a lens light path; and the detection bandwidth of the line-scan digital camera is matched with the pixels. On the premise that the imaging quality is guaranteed, the design and manufacturing cost of the system is remarkably reduced, and then efficient balance between high-performance imaging and low cost is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optics, and in particular to a spectrometer for optical coherence tomography. BACKGROUND

[0002] As the core component of spectral domain optical coherence tomography (SD-OCT) system, the performance of spectrometer directly determines the imaging quality and detection ability of the system. SD-OCT technology emits light signals through a broadband light source, and the reflected light signals form an interference spectrum after being reflected by the sample. The spectrometer then completes the light detection, and finally reconstructs the tomographic image through Fourier transform. This technology breaks through the imaging speed bottleneck of traditional time-domain OCT, has micron-level resolution and real-time high-sensitivity imaging capability, and is widely used in biomedical fields such as ophthalmology and dermatology, and gradually expands to the field of industrial non-destructive testing. However, the existing spectrometer design generally faces two types of high-cost dilemmas: one relies on high-precision customized optical elements, and the other optimizes aberration by adding multiple optical devices, both of which lead to an increase in system complexity and a significant cost of core components.

[0003] In the design of optical coherence tomography (OCT) spectrometer, different optical schemes have significant trade-offs between performance and cost. Specifically: Patent scheme analysis: A patent titled "Small Airy Spot Spectrometer for Optical Coherence Tomography" proposes an optical design that uses a four-lens focusing lens group. However, the curvature parameters and optical materials of these lenses are not regular commercial standard specifications, and they need to rely on customized processing, which significantly increases the cost of system manufacturing. Although this design focuses on small Airy spots (i.e., high spatial resolution) as its core advantage, the need for customization limits its economic feasibility and promotes its feasibility.

[0004] Paper scheme comparison: Another paper titled "Design and implementation of a low-cost portable OCT system" proposes a low-cost alternative. This scheme uses two double-cemented lenses as the focusing lens group and uses a concave mirror for collimation design. Its advantage is that all optical elements are commercial standard parts, which greatly reduces the cost and adapts to the needs of portable systems; but the cost is a larger focusing spot radius, which sacrifices the spatial resolution to some extent.

[0005] Comprehensive comparison: In summary, the two schemes represent different technical paths of high performance and high cost, and low cost and moderate performance. The patent scheme optimizes the spot quality by customizing the lens, while the paper scheme controls the cost with commercial components, reflecting the inherent contradiction between resolution and economy in the design of OCT spectrometer. SUMMARY

[0006] The embodiment of the present application provides a spectrometer for optical coherence tomography, which significantly reduces the design and manufacturing cost of the system under the premise of ensuring the imaging quality.

[0007] According to the embodiment of the present application, a spectrometer for optical coherence tomography is provided, which sequentially comprises a collimating unit, a grating light splitting element, a mirror, a focusing unit and a linear array camera according to the light path. The collimating unit realizes smooth transition of the incident angle and the exit angle of the light in the collimating unit by optimizing the distance between the lens and the light source and the air gap between the two lenses; The grating light splitting element realizes separation of different waveband light signals by adopting high line logarithm design, thereby reducing the focal length requirement of the subsequent focusing system; The mirror folds back the light path, so that the collimating end and the detection part are arranged in parallel, and the overall length of the system is effectively shortened by folding the light path; The focusing unit distributes the positive and negative optical powers of each element, and suppresses the aberration of the lens light path; The linear array camera matches the detection bandwidth with the pixels.

[0008] Further, the collimating unit is composed of two lenses, the first lens is a meniscus lens, and the curvature radius thereof is larger and faces away from the light source; the second lens is an aspheric lens, and the plane side thereof faces the light source.

[0009] Further, the focal length range of the second lens is 50-100mm.

[0010] Further, the grating light splitting element adopts a transmission grating structure.

[0011] Further, the line density of the transmission grating structure is 1000-2000lp / mm.

[0012] Further, the first lens is a plano-convex lens, the focal length range thereof is 100mm to 150mm, and the smaller curvature radius thereof faces the collimating light source.

[0013] Further, the second lens is a plano-convex lens, the focal length range thereof is 200mm to 250mm, and the convex surface thereof faces the light source, and cooperates with the first lens to bear the positive power and chromatic aberration correction.

[0014] Further, the third lens is a plano-concave lens, the focal length range thereof is -150mm to -200mm, and balances the field curvature residual aberration.

[0015] The spectrometer for optical coherence tomography in the embodiment of the present application adopts a near-infrared waveband light source, which is transmitted to the spectrometer module through an optical fiber jumper and finally signal acquisition is completed by a high-speed linear array camera. On the premise of ensuring the imaging quality, the design and manufacturing costs of the system are significantly reduced, and then the efficient balance of high-performance imaging and low cost is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which are included to provide a further understanding of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and together with the description serve to explain the present application. In the drawings: Figure 1 Optimized optical structure of the spectrometer: 1 is a meniscus lens, 2 is a non-spherical lens with a focal length of 50-100 mm, 1 and 2 constitute a collimating lens group; 3 is a transmission grating, 4 is a plane mirror; 5 is a plano-convex lens with a focal length of 100 mm-150 mm, 6 is a plano-convex lens with a focal length of 200 mm-250 mm, 7 is a plano-concave lens with a focal length of -150 mm--200 mm, devices 5, 6 and 7 constitute a focusing lens group; 8 is an image plane position; Figure 2 Point array diagram of minimum wavelength, center wavelength and maximum wavelength; Figure 3 MTF diagram of each wavelength; Figure 4 Each wavelength circle energy diagram. DETAILED DESCRIPTION

[0017] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0018] It is to be understood that the terms "first", "second", and the like, used in the description and the claims of the application, as well as the above-described drawings, are used to distinguish between similar objects, not necessarily described in their specific order or sequence. It should be understood that the data thus used can be interchanged, where appropriate, so that the embodiments of the application described herein can be implemented in other than the order illustrated or described herein. Furthermore, the terms "include" and "have" and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that includes a list of steps or units is not necessarily limited to those steps or units that are clearly listed, but can include other steps or units that are not clearly listed or inherent to such processes, methods, products, or apparatuses.

[0019] The present application aims at the problem of high cost of the spectrometer, a core component of spectral domain optical coherence tomography (SD-OCT) system, and proposes a low-cost solution based on commercial lenses and optical design optimization. Existing spectrometer designs generally face two types of high-cost dilemmas: one is to rely on high-precision customized optical elements, and the other is to optimize aberration by adding multiple optical devices, which leads to an increase in system complexity and a significant increase in the cost proportion of core components. The present application realizes cost control through two key designs: one is to use standardized commercial lenses to replace customized elements, and the other is to optimize the focusing / collimating unit structure (to control the number of lens groups to less than 4 through positive-negative lens combination), reducing the amount of optical devices. Under the premise of ensuring imaging quality, the manufacturing cost of the spectrometer is significantly reduced.

[0020] The present application proposes a low-cost optical design scheme based on commercial standardized elements, which realizes dynamic regulation of the performance of the spectrometer (such as resolution, aberration) by optimizing lens parameters, spacing, and orientation. This scheme significantly reduces the design and manufacturing cost of the system under the premise of ensuring imaging quality, thereby achieving an efficient balance between high-performance imaging and low cost.

[0021] A typical OCT spectrometer usually works in the infrared or near-infrared band, and its spectral resolution and detection depth are inversely proportional to the spectral main wavelength, and are positively correlated. The spectrometer described in the present application uses a near-infrared band light source, which is transmitted to the spectrometer module through an optical fiber jumper, and finally the signal is collected by a high-speed linear array camera. The core structure of the system is shown in Figure 1 , which includes a collimating unit, a grating light splitting element, a mirror, a focusing unit, and a linear array camera, and the specific design is as follows: I. Collimating unit: double lens cooperative optimization of wavefront quality The collimation unit is composed of two lenses: element 1 adopts a commercial meniscus lens, the curvature radius of which is large and faces away from the light source; element 2 is an aspheric lens (focal length range 50-100mm), the plane side of which faces the light source. In the design, the aspheric lens mainly undertakes the collimation power: by optimizing the distance between the meniscus lens and the light source and the air gap between the two lenses, the incidence angle and the exit angle of the light in the collimation unit are smoothly transitioned, thereby effectively correcting the spherical aberration of the fiber collimation lens. Under this design, the collimated light spot diameter is greater than 20mm: the large light spot size can effectively reduce the Airy disk diameter, thereby improving the resolution of subsequent imaging.

[0022] II. Grating light splitting element: key to high efficiency and miniaturization The grating light splitting element (element 3) adopts a transmission grating structure, which has multiple advantages over a reflective grating: higher diffraction efficiency, avoidance of the problem of ghost lines caused by surface reflection of the reflective grating, and insensitivity to the polarization state of the incident light. The grating has a simple optical path structure and low energy loss of the light source, and the ruling density ranges from 1000 to 2000 lp / mm. The high line number design can more efficiently separate light signals of different wavelengths, effectively reducing the focal length requirement of the subsequent focusing system, and providing strong support for the miniaturization design of the spectrometer.

[0023] III. Reflective mirror: optical path folding and layout optimization Element 4 is a reflective mirror, which has the core function of folding the optical path to make the collimation end and the detection part parallel; at the same time, it effectively shortens the overall length of the system and improves the compactness of the structure.

[0024] IV. Focusing unit: multi-lens collaborative correction of aberration The focusing unit adopts a positive-negative lens sequence composed of three lenses, which effectively suppresses the aberration of the lens optical path by reasonably distributing the positive and negative focal powers of each element. Compared with the scheme in which a single lens undertakes the positive focal power of the system, the present design distributes the positive focal power through two positive lenses: first, it reduces the surface curvature of a single lens to suppress spherical aberration and coma; second, it increases the degree of freedom of the air gap in the optical path (which can be adjusted as an optimization variable), improving the design flexibility. In addition, a negative lens (flat field mirror) is added after the two positive lenses to compensate for the field curvature using its negative focal power, ensuring the flatness of the image surface. The specific element configuration and design details are as follows: Element 5 is a plano-convex lens (focal length range 100mm-150mm), the smaller curvature radius of which faces the collimation light source to optimize the focusing performance.

[0025] Element 6 is a plano-convex lens (focal length range 200mm-250mm), which cooperates with element 5 to undertake the positive focal power and chromatic aberration correction; to further reduce the spherical aberration, the convex side faces the light source.

[0026] Element 7 is a flat concave lens (focal length -150mm-200mm), focusing on balancing the field curvature and other residual aberrations, ensuring the uniformity of the light spot received by the detector target surface.

[0027] Five, linear array camera: detection bandwidth and pixel matching Element 8 is the installation position of the linear array camera chip, and the pixel size of the selected linear array camera is 14μm. The combination of the linear array camera photosensitive chip size and the spectral characteristics of the light source ultimately determines the system detection bandwidth of the spectrometer.

[0028] As shown in Figure 2 The point diagram of the present application at the center wavelength, the maximum wavelength and the minimum wavelength shows that the focused light spot corresponding to each wavelength is completely converged within the Airy disk range, and the light spot size is much smaller than the detector pixel size (14μm). This result shows that the dispersion characteristics of the actual focused light spot of the system have approached the diffraction limit level, and the imaging quality is excellent.

[0029] The modulation transfer function (MTF) is further used to verify the contrast performance of the system imaging: as shown in Figure 3 At the camera detection cutoff frequency (35.7lp / mm), the MTF value of the spectrometer is still better than 0.7, indicating that the system has good contrast retention capability within the detector response bandwidth.

[0030] The energy circle test result ( Figure 4 ) shows that within the pixel size (14μm), the energy circle efficiency of the target wavelength approaches the diffraction limit, verifying the high efficient collection and utilization capability of the system for light energy.

[0031] The key points and points to be protected of the present application are: The core innovation of the present application lies in the synergistic optimization design of commercial standard optical elements, which breaks the inherent contradiction between high performance and high cost of the SD-OCT spectrometer, which is embodied in the following three aspects: 1) Low-cost high-performance design of collimation unit: using a combination structure of meniscus lens and aspheric positive lens, through curvature parameter optimization and synergistic control of element air gap, while reducing the demand for customized processing, the collimation spot quality (diameter>20mm) is ensured, and the material and assembly cost of the collimation module is effectively reduced.

[0032] 2) Compact optimization of optical path layout: the system layout is optimized by folding the optical path with a mirror, reducing the overall length of the system, and optimizing the structure layout.

[0033] 3) Combination of focusing units for aberration correction: The combination of positive and negative lens structures is adopted, the device surface is optimized (for example, the convex surface of the plano-convex lens faces the light source), and the three-level aberration correction scheme (chromatic aberration, field curvature, spherical aberration) is adopted to balance the residual aberration and ensure that the energy circle efficiency is close to the diffraction limit (> 90%), thereby improving the signal-to-noise ratio and imaging resolution of the system. The core protection point of the present application is around the synergistic optimization design of commercial standard optical elements, aiming to solve the contradiction between "high performance-high cost" of the SD-OCT spectrometer, which is embodied in three key aspects: first, in the design of the collimation unit, through the combination of meniscus lens and aspherical positive lens, combined with curvature parameter optimization and dynamic regulation of element air gap, the collimation spot diameter is greater than 20mm, while reducing the demand for customized processing to reduce the cost of material processing; second, in the light path layout optimization, the overall length of the system is reduced by folding the light path with a mirror, realizing compact structure; finally, in the aberration correction of the focusing unit, the positive and negative lens combination (such as plano-convex lens, plano-convex lens and plano-concave lens) is adopted, and the three-level aberration correction (chromatic aberration, field curvature, spherical aberration) is realized through the surface orientation optimization (such as the smaller curvature radius surface facing the light source), ensuring that the energy circle efficiency is close to the diffraction limit (> 90%), and improving the signal-to-noise ratio and imaging resolution. Overall, this systematic innovation not only covers the hardware structure and method process, but also forms a complete technical solution through quantitative performance standards (such as spot size, field curvature control), realizing cost-effective breakthrough and application generalization.

[0034] Compared with the prior art, the present application has the following advantages: The core advantage of the present application is that the cost of the spectrometer is significantly reduced through the synergistic optimization design of commercial standard optical elements, which is embodied in the following three aspects: Customized component replacement cost reduction: The collimation unit adopts the combination design of commercial meniscus lens (element 1) and aspherical lens (element 2); the focusing unit selects commercial standard elements such as plano-convex lens, plano-convex lens and plano-concave lens (elements 5-7), without the need for customized processing, directly reducing the cost of component procurement and manufacturing.

[0035] Design optimization for efficiency and cost reduction: Through the aberration correction of negative lens and aspherical lens, the folding of light path with a mirror (shortening the length of the system) and the multi-module optimization design of positive and negative lens combination, the dependence on high-precision customized components is reduced under the premise of ensuring the imaging quality (Airy spot size <14um, MTF >0.7, energy circle efficiency close to the diffraction limit), thereby reducing the technical threshold and system complexity.

[0036] Performance cost optimal balance: the invention relies on the precise parameter matching of commercial components (such as reducing the Airy disk size of a collimated light spot greater than 20mm, multi-lens cooperative correction of aberration), while maintaining high performance such as high resolution, low aberration, avoiding additional customization overhead, realizing the optimal solution of low cost and available performance.

[0037] The above-mentioned embodiment numbers of the present application are only for description, not representing the advantages and disadvantages of the embodiments.

[0038] In the above-mentioned embodiments of the present application, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the relevant description of other embodiments.

[0039] In several embodiments provided in the present application, it should be understood that the disclosed technical contents can be implemented by other ways. Among them, the system embodiments described above are only schematic, for example, the division of units can be a logical function division, and actual implementation can have another division way, for example, a plurality of units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the units or modules shown or discussed can be indirect coupling or communication connection through some interfaces, and can be electrical or other forms.

[0040] The units described as separate components can or can not be physically separated, and the components shown as units can or can not be physical units, that is, they can be located in one place, or they can be distributed to multiple units. According to actual needs, part or all of the units can be selected to achieve the purpose of the present embodiment scheme.

[0041] In addition, each functional unit in each embodiment of the present application can be integrated in one processing unit, or each unit can exist physically, or two or more units can be integrated in one unit. The above integrated unit can be realized in the form of hardware or in the form of software functional unit.

[0042] The integrated unit, if implemented in the form of a software function unit and sold or used as an independent product, can be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the present application, essentially or in other words, the part that contributes to the prior art or the whole or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium, including a plurality of instructions to make a computer device (which can be a personal computer, a server or a network device, etc.) execute all or part of the steps of the embodiments of the present application. The aforementioned storage medium includes: a U disk, a read-only memory (ROM, Read-Only Memory), a random access memory (RAM, Random Access Memory), a mobile hard disk, a magnetic disk or an optical disk, and various media that can store program codes.

[0043] The above is only the preferred embodiment of the present application, it should be pointed out that, for those skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A spectrometer for optical coherence tomography, characterized in that, According to the light path, it includes, in sequence: collimation unit, grating beam splitter, reflector, focusing unit, and line scan camera; among which: The collimation unit optimizes the distance between the lens and the light source, as well as the air gap between the two lenses, to achieve a smooth transition between the incident angle and the exit angle of light in the collimation unit. The grating beam splitter uses a high line logarithm design to separate optical signals of different wavelengths, reducing the focal length requirement of the subsequent focusing system; The reflector folds the light path back, making the collimating end and the detection part parallel to each other, and the overall length of the system is effectively shortened by folding the light path; The focusing unit assigns positive and negative optical power to each element to suppress aberrations in the lens optical path; Linear scan camera detection bandwidth is matched with pixels.

2. The spectrometer for optical coherence tomography according to claim 1, characterized in that, The collimation unit consists of two lenses. The first lens is a meniscus lens with a large radius of curvature and faces away from the light source. The second lens is an aspherical lens with its planar side facing the light source.

3. The spectrometer for optical coherence tomography according to claim 2, characterized in that, The second lens has a focal length range of 50-100mm.

4. The spectrometer for optical coherence tomography according to claim 1, characterized in that, The grating beam splitter adopts a transmission grating structure.

5. The spectrometer for optical coherence tomography according to claim 4, characterized in that, The grating density ranges from 1000 to 2000 lp / mm.

6. The spectrometer for optical coherence tomography according to claim 5, characterized in that, The first lens is a plano-convex lens with a focal length ranging from 100mm to 150mm, and its smaller radius of curvature faces the collimating light source.

7. The spectrometer for optical coherence tomography according to claim 6, characterized in that, The second lens is a plano-convex lens with a focal length range of 200mm to 250mm. Its convex surface faces the light source and works in conjunction with the first lens to perform positive focal length and chromatic aberration correction.

8. The spectrometer for optical coherence tomography according to claim 7, characterized in that, The third lens is a plano-concave lens with a focal length of -150mm to -200mm to balance the residual aberration of the field curvature.

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