Large-view-field relay system based on graded-index lens and design method

Abstract

The invention discloses a large-view-field relay system based on a graded-index lens and a design method, and relates to the technical field of optics, the system comprises an object plane, a graded-index lens, an optical cementing layer, a plano-concave lens and an image plane which are coaxially arranged in sequence; the gradient refractive index lens and the plano-concave lens are connected through an optical cementing layer. According to the relay system, on the premise that the diffraction limit is met, the maximum effective view field radius is expanded to 0.15 mm, and the view field is improved by about 76% compared with the view field of a single graded-index lens.

Description

Technical Field

[0001] This invention relates to the field of optical technology, specifically to a large field-of-view relay system and its design method based on a graded refractive index lens. Background Technology

[0002] Miniature fluorescence microscopy is a crucial tool in modern neuroscience for analyzing changes in specific neural circuits in animals under natural behavior. For deep brain regions located millimeters below the cortex (such as the hippocampus and hypothalamus), which exceed the imaging depth of conventional microscopes, relay lenses must be implanted within the brain to transmit excitation light and fluorescence signals. Gradient-index lenses, with their tiny size, flat-end design, and radial self-focusing optical properties, have become indispensable relay elements in deep brain imaging systems.

[0003] In the prior art, a typical approach is to combine a plano-convex lens with a GRIN lens into a miniature objective lens. This design increases the numerical aperture (NA) of the system by utilizing the positive optical power of the plano-convex lens, while using the GRIN lens to correct the spherical aberration introduced by the plano-convex lens, thereby improving the resolution to the diffraction limit level and clearly observing the dendritic spine structure of hippocampal neurons.

[0004] While using a front-end plano-convex lens improves resolution, it also causes a sharp accumulation of Petzwald curvature, which macroscopically manifests as a severe inward bending of the system's focal plane. This results in a smaller effective field of view. Summary of the Invention

[0005] To address the physical limitations of severe Petzwald field curvature and off-axis astigmatism inherent in single GRIN lenses, this invention proposes a large field-of-view relay system and its design method based on a graded-index lens.

[0006] The technical solution of the present invention is: a large field-of-view relay system based on a graded refractive index lens includes an object plane, a graded refractive index lens, an optical cementing layer, a plano-concave lens and an image plane arranged coaxially in sequence;

[0007] The gradient refractive index lens and the plano-concave lens are connected by an optical adhesive layer.

[0008] Furthermore, the graded refractive index lens uses a radially graded refractive index material with a central refractive index of 1.62, a self-focusing constant of 0.6, and a fourth-order coefficient of 0.21.

[0009] Furthermore, the optical adhesive layer uses a UV-curable adhesive with a refractive index of 1.5597.

[0010] Furthermore, the plano-concave lens uses heavy lanthanum flint glass.

[0011] Furthermore, the front and rear surfaces of a graded-index lens are both planar; the front surface of a plano-concave lens is planar, and its rear surface is spherical.

[0012] Based on the above system, this invention also proposes a design method for a large field-of-view relay system based on a graded refractive index lens, comprising the following steps:

[0013] S1. Perform basic optimization on the large field-of-view relay system;

[0014] S2. Based on the optimized large field-of-view relay system, the field of view is extended.

[0015] Furthermore, in S1, the basic optimization specifically involves optimizing the central field of view and paraxial field of view of the large field of view relay system so that the center point map converges to within the Airy disk.

[0016] Furthermore, in S2, the field of view expansion is specifically performed by setting the optimization weight of each field of view of the large field of view relay system to 1, reducing the optimization weight of the central field of view and increasing the optimization weight of the edge field of view, and using operands to extract and adjust the Strell ratio of the edge field of view to be greater than or equal to 0.8.

[0017] The beneficial effects of this invention are:

[0018] (1) Significantly improved field of view: Under the premise of satisfying the diffraction limit, the relay system of the present invention extends the maximum effective field of view radius to 0.15 mm, which is about 76% higher than that of a single graded refractive index lens.

[0019] (2) Maintaining excellent imaging contrast: The Airy disk radius of the present invention is maintained at 1.22µm, and the modulation transfer function value is stable at 0.3 or above at the spatial frequency (410 lp / mm) corresponding to the resolution limit, which is far beyond the resolvable threshold of 0.1 of conventional photosensitive devices.

[0020] (3) Good engineering manufacturability: Monte Carlo tolerance analysis verified that the probability of the modulation transfer function being greater than 0.37 (i.e. yield) of the present invention under conventional processing and assembly tolerance is stable at over 90%, which has extremely high potential for large-scale application. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a large field-of-view relay system based on a graded refractive index lens;

[0022] Figure 2 A graph showing the yield rate;

[0023] Figure 3 A comparison of the MTF curves of a single GRIN lens with a field of view of 0.085mm and the large field of view relay system of the present invention with a field of view of 0.15mm.

[0024] Figure 4 This is a flowchart illustrating the design method of a large field-of-view relay system based on a graded-index lens. Detailed Implementation

[0025] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0026] like Figure 1 As shown, the present invention provides a large field-of-view relay system based on a graded refractive index lens, comprising an object plane 1, a graded refractive index lens 2, an optical cement layer 3, a plano-concave lens 4, and an image plane 5 arranged coaxially in sequence.

[0027] The graded refractive index lens 2 and the plano-concave lens 4 are connected by an optical adhesive layer 3.

[0028] The GRIN lens 1 serves as the core light transmission and self-focusing element, and a plano-concave lens 4 with negative optical power is set behind it to actively compensate for the Petzwald field curvature caused by the front group and expand the effective imaging field of view.

[0029] The system's operating wavelength was set to 920nm, which is commonly used in two-photon fluorescence imaging, and the thickness of the optical adhesive layer was set to approximately 0.001mm to ensure that the actual assembly performance was completely consistent with the theoretical design.

[0030] GRIN lens 2 is made of radially graded refractive index material, with a central refractive index of... The refractive index is 1.62, the self-focusing constant is 0.6, and the fourth-order coefficient is 0.21. The plano-concave lens 4 is made of heavy lanthanum flint glass H-ZLAF90, and the optical adhesive layer 3 uses UV-curable adhesive NOA61 with a refractive index n=1.5597.

[0031] The front and rear surfaces of GRIN lens 2 are both flat. The front surface of plano-concave lens 4 is flat, and the rear surface is spherical.

[0032] From the GRIN lens to the plano-concave lens, the optical surfaces are arranged from front to back as the first to the fourth surface. The fourth surface is a standard sphere with a radius of curvature of 0.6 mm; the first, second, and third surfaces are all standard planes; the medium between the first and second surfaces is a graded refractive index material with a continuous radial refractive index distribution (graded three).

[0033] In this embodiment of the invention, the gradient refractive index lens 2 is made of a radially gradient refractive index material, with a central refractive index of 1.62, a self-focusing constant of 0.6, and a fourth-order coefficient of 0.21.

[0034] In this embodiment of the invention, the optical adhesive layer 3 is made of UV-curable adhesive with a refractive index of 1.5597.

[0035] In this embodiment of the invention, the plano-concave lens 4 is made of heavy lanthanum flint glass.

[0036] In this embodiment of the invention, the front and rear surfaces of the gradient refractive index lens 2 are both planar; the front surface of the plano-concave lens 4 is planar, and its rear surface is spherical.

[0037] The lens data for this invention is shown in Table 1. The wavelength chosen is 920nm, commonly used in two-photon fluorescence imaging. The plano-concave lens is made of lanthanum heavy metal flint glass (H-ZLAF90) with a high refractive index to obtain the required negative optical power within a limited micro-space. The GRIN lens and the plano-concave lens are connected using UV-curable adhesive (NOA61) with a thickness of approximately 0.001mm to ensure that the actual assembly performance matches the theoretical design.

[0038] Table 1

[0039] The values ​​of each parameter in this invention can fluctuate within a certain range, and the tolerance allocation is shown in Table 2.

[0040] Table 2

[0041] Tolerances were assigned based on the data in Table 2, and 1000 Monte Carlo tolerance analyses were performed. Figure 2 As shown, the relay system has a probability of making the MTF greater than 0.37 more than 90% of the time, and its overall manufacturability is good.

[0042] The relay system of this invention, while satisfying the diffraction limit, extends the maximum effective field of view radius to 0.15 mm, representing an approximately 76% improvement compared to a single GRIN lens. A comparison of its MTF curve with the maximum field of view of a single GRIN lens is shown in the figure below. Figure 3 As shown.

[0043] Both the conventional GRIN lens and the Airy disk radius of this invention are 1.22µm. At the spatial frequency corresponding to the resolution limit (410lp / mm), the modulation transfer function (MTF) value of the conventional GRIN lens at a field of view of 0.085mm and the modulation transfer function (MTF) value of this invention at a field of view of 0.15mm are both stable above 0.3.

[0044] The invention has been verified by Monte Carlo tolerance analysis. Under normal processing and assembly tolerances, the probability of MTF being greater than 0.37 (i.e., yield rate) of the system is stable at over 90%, which shows that it has extremely high potential for large-scale application.

[0045] Based on the above systems, such as Figure 4As shown, this invention also proposes a design method for a large field-of-view relay system based on a graded-index lens, comprising the following steps:

[0046] S1. Perform basic optimization on the large field-of-view relay system;

[0047] S2. Based on the optimized large field-of-view relay system, the field of view is extended.

[0048] In this embodiment of the invention, in S1, the basic optimization specifically involves optimizing the central field of view and paraxial field of view of the large field of view relay system so that the center point map converges to within the Airy disk.

[0049] In this embodiment of the invention, in S2, the field of view expansion is specifically performed by setting the optimization weight of each field of view of the large field of view relay system to 1, reducing the optimization weight of the central field of view and increasing the optimization weight of the edge field of view, and using operands to extract and adjust the Strell ratio of the edge field of view to be greater than or equal to 0.8.

[0050] The length of the GRIN lens, the fourth-order coefficient, the thickness of the plano-concave lens, the radius of curvature, and the image distance were set as variables for optimization.

[0051] In the joint optimization phase of the system's optical power, an evaluation function was constructed based on wavefront difference. In the initial optimization phase, to avoid the algorithm getting trapped in local minima and to ensure practical fabrication feasibility, operands (MNCG, MXCG, MNEG, MXEG) were used to strictly limit the center and edge thicknesses of the plano-concave lens to a fabricationable range of 0.1 mm to 1.5 mm. This prevented the lens from becoming too thin, which could lead to fabrication breakage, or too thick, which could cause volume redundancy. The thickness of surface 4 (i.e., image distance) was also constrained to always be greater than 0.1 mm.

[0052] In terms of specific optimization strategies, an approach of gradually expanding the field of view from the inside out was adopted. First, basic optimization was performed on the central field of view and the paraxial field of view to guide the system's optical power to complete the initial allocation and ensure that the central point map converges to within the Airy disk.

[0053] After the system acquires initial convergence capability, the field of view radius is gradually expanded outward. During the field of view expansion process, the Strel ratio (SR) of each field of view is extracted using the STRH operand. In the initial optimization phase, each field of view is assigned an equal optimization weight (i=1). As optimization progresses, the Strel ratio (SR) of the central field of view first reaches above 0.95, but due to astigmatism and field curvature, the SR of the peripheral fields of view remains below the diffraction limit standard of 0.8. Therefore, this paper gradually reduces the weight of the central field of view to 0.5 to release optimization degrees of freedom, while increasing the weight of the peripheral fields of view in a stepwise manner to 3, guiding the optical power allocation of the plano-concave lens to tilt towards compensating for the peripheral field curvature. Finally, by introducing an operand greater than the target value (OPGT), the peripheral field of view is forcibly constrained to have an S ≥ 0.8. When the field of view expands to 0.15 mm, the correction capability of the plano-concave lens approaches its limit. Further expanding the field of view at this point will prevent the Strell ratio of the edge field of view from increasing above 0.8. If the weights are adjusted to forcibly optimize the edge field of view, the imaging quality of the center field of view will fail to meet the diffraction limit. Therefore, the maximum field of view radius of this relay system is fixed at 0.15 mm. After rounding the lens parameters, the lens data for the large field of view relay system in Table 1 can be obtained.

[0054] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A large field-of-view relay system based on a graded-index lens, characterized in that, It includes an object plane (1), a graded refractive index lens (2), an optical cement layer (3), a plano-concave lens (4), and an image plane (5) arranged coaxially in sequence; The gradient refractive index lens (2) and the plano-concave lens (4) are connected by an optical adhesive layer (3).

2. The large field-of-view relay system based on a graded-index lens according to claim 1, characterized in that, The gradient refractive index lens (2) is made of radially gradient refractive index material, with a central refractive index of 1.62, a self-focusing constant of 0.6, and a fourth-order coefficient of 0.

21.

3. The large field-of-view relay system based on a graded-index lens according to claim 1, characterized in that, The optical adhesive layer (3) is made of UV-curable adhesive with a refractive index of 1.5597.

4. The large field-of-view relay system based on a graded-index lens according to claim 1, characterized in that, The plano-concave lens (4) is made of heavy lanthanum flint glass.

5. The large field-of-view relay system based on a graded-index lens according to claim 1, characterized in that, The front and rear surfaces of the gradient refractive index lens (2) are both planar; the front surface of the plano-concave lens (4) is planar, and its rear surface is spherical.

6. A design method for a large field-of-view relay system based on a graded-index lens, characterized in that, Includes the following steps: S1. Perform basic optimization on the large field-of-view relay system; S2. Based on the optimized large field-of-view relay system, the field of view is extended.

7. The design method for a large field-of-view relay system based on a graded-index lens according to claim 6, characterized in that, In S1, the basic optimization specifically involves optimizing the central field of view and paraxial field of view of the large field of view relay system so that the center point map converges to within the Airy disk.

8. The design method of a large field-of-view relay system based on a graded-index lens according to claim 6, characterized in that, In S2, the field of view expansion is specifically performed by setting the optimization weight of each field of view of the large field of view relay system to 1, reducing the optimization weight of the central field of view and increasing the optimization weight of the edge field of view, and using operands to extract and adjust the Strell ratio of the edge field of view to be greater than or equal to 0.8.

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