Integrated super-resolution read-write objective lens and preparation method thereof

Abstract

The invention provides an integrated super-resolution read-write objective lens and a preparation method thereof, the integrated super-resolution read-write objective lens is a single diffractive optical element, the surface of the element is provided with a preset microstructure, the microstructure is a binary or multi-step stepped embossment structure, and the surface of the element is provided with a plurality of microstructures. The microstructure is designed to simultaneously implement at least two optical transformations on an incident beam. According to the invention, functions of focusing, spiral phase modulation and the like simultaneously occur on the surface of the same element, light beams do not need to be transmitted among different elements, and phase distortion caused by effects of Fresnel diffraction and the like is eliminated; secondly, the excitation light and the suppression light pass through the same integrated element, and the relative position relation of the excitation light and the suppression light is accurately fixed by a microstructure on the surface of the element, so that the auto-collimation of a light path is realized, and the stability and robustness of the system are improved; besides, the negative dispersion characteristic of the diffractive optical element is utilized, inherent dispersion of the material is efficiently compensated or eliminated on a single element, a complex lens group is not needed, and an efficient and simple achromatic scheme is provided.

Description

Technical Field

[0001] This invention relates to the field of super-resolution optical imaging technology, specifically to an integrated super-resolution reading and writing objective lens and its fabrication method. Background Technology

[0002] In recent years, super-resolution optical imaging techniques, represented by stimulated emission depletion (STED) microscopy, have made significant progress. They have successfully broken through the Abbe diffraction limit of traditional optical microscopes, enabling in vivo and dynamic observation of subcellular structures at the nanoscale. The core principle of STED technology lies in spatially selective fluorescence suppression. In this technique, a Gaussian-distributed excitation beam excites fluorescent molecules in a diffraction-limited region of the sample to an excited state. Simultaneously, a ring-shaped suppression beam illuminates the same region. This suppression beam, with its wavelength located at the red end of the fluorescence emission spectrum, can return fluorescent molecules in the region surrounding the excitation focus to their ground state through stimulated emission, thus preventing these molecules from emitting spontaneous fluorescence. In this way, only fluorescent molecules located near the zero point of the suppression spot can emit fluorescence signals normally. Ultimately, the signal acquisition area is effectively compressed to a size much smaller than the diffraction limit, thereby achieving super-resolution imaging.

[0003] To achieve the above principle, existing STED microscope systems typically employ a combination of discrete components in the optical path. This approach generally includes the following core components: a high numerical aperture objective lens, used to focus the excitation and suppression light onto the sample and collect the fluorescence signal; a spiral phase plate, placed in the suppression light's optical path, used to shape the suppression light into a vortex beam; and an achromatic system or spatial light modulator, used to correct for chromatic aberration caused by the different wavelengths of the excitation and suppression light.

[0004] However, this cascaded design based on discrete components suffers from a series of inherent, interconnected flaws that limit the stability, ease of use, and widespread adoption of STED technology. These flaws primarily stem from the physical spatial separation between the various optical components:

[0005] First, the spatial separation of the spiral phase plate and the objective lens introduces significant cooperative errors. Ideally, the spiral phase plate should be precisely placed on the back focal plane of the objective lens to ensure that the pure spiral phase distribution is Fourier transformed into a high-quality vortex focal spot. However, in actual assembly, there will always be an unavoidable physical distance between them. When the beam propagates at this distance, Fresnel diffraction occurs, resulting in complex diffraction phases. This phase distortion causes the intensity of the suppressed light center on the object plane to be non-zero or its shape to be asymmetrical, thereby reducing the suppression efficiency.

[0006] Secondly, the alignment accuracy requirements of the entire optical path are extremely stringent and its stability is poor. The super-resolution effect of STED technology highly depends on the precise coaxial alignment of the excitation spot and the suppression spot's center zero point, requiring alignment accuracy at the nanometer level. In discrete systems, minute displacements or tilts of the components behind the shaping mirror caused by installation accuracy, ambient temperature, and mechanical vibration are amplified step by step by the optical path, ultimately leading to misalignment at the focal point. This latter type of high-frequency influence necessitates the use of higher-frequency servo correction in the system, making it difficult to maintain optimal performance.

[0007] Finally, chromatic aberration correction schemes are complex and costly. In order to accurately focus excitation and suppression light of different wavelengths onto the same point, traditional achromatic objective lens designs are extremely complex, requiring the use of multiple special optical glasses to form a lens group of more than ten lenses. This not only makes the objective lens bulky and expensive, but its correction effect is also usually limited to specific wavelength pairs.

[0008] Therefore, there is an urgent need in the field for a technical solution that can fundamentally eliminate the aforementioned problems caused by discrete components and their spatial separation. Summary of the Invention

[0009] In view of this, the present invention provides an integrated super-resolution reading and writing objective lens and its preparation method, so as to at least solve the above-mentioned technical problems.

[0010] According to a first aspect of the present invention, an integrated super-resolution reading and writing objective lens is provided, the objective lens being a single diffractive optical element, the surface of the diffractive optical element having a predetermined microstructure, the microstructure being a binary or multi-level stepped relief structure, the microstructure being designed to simultaneously achieve at least two optical transformations on an incident light beam, including: a focusing transformation to focus the light beam onto a predetermined focal plane; and a phase modulation transformation to apply a spiral phase to the light beam to form a vortex beam.

[0011] Optionally, the microstructure is also designed to achieve a third optical transformation, including: an achromatic transformation to correct chromatic aberration, such that the excitation beam of the first wavelength and the suppression beam of the second wavelength are confocal on the predetermined focal plane; wherein the achromatic transformation is achieved by designing the microstructure so that the excitation beam of the first wavelength and the suppression beam of the second wavelength operate at different diffraction orders.

[0012] Optionally, when the excitation beam of the first wavelength is incident, the objective lens forms a dot-shaped spot with maximized central light intensity at the predetermined focal plane; when the suppression beam of the second wavelength is incident, the objective lens forms an annular spot at the predetermined focal plane, wherein the ratio of the central light intensity of the annular spot to the maximum light intensity of the annular spot is less than or equal to 0.05.

[0013] Optionally, the microstructure is formed by spatially encoding a total phase function, which is a mathematical superposition of at least one lens phase function and a spiral phase function.

[0014] Optionally, the total phase function further includes an achromatic phase function to compensate for the inherent dispersion of the diffractive optical element or the material dispersion of the substrate material.

[0015] According to a second aspect of the present invention, a system for a stimulated emission depletion super-resolution microscope is provided, the system employing the super-resolution read / write objective as described in the first aspect above as its read / write objective.

[0016] According to a third aspect of the present invention, an integrated super-resolution reading and writing objective lens is provided, comprising: acquiring pattern data of microstructures on the surface of the super-resolution reading and writing objective lens; and forming, in a single step, a microstructure corresponding to the pattern data on at least one surface of a provided optical substrate using micro-nano fabrication technology, so that the super-resolution reading and writing objective lens can simultaneously achieve focusing, helical phase modulation and achromatic functions.

[0017] Optionally, pattern data of the microstructure on the surface of the super-resolution reading lens is obtained through the following steps: a. Define a target focusing function and determine a lens phase function based on the target focusing function; b. Define a target vortex beam generation function and determine a spiral phase function based on the target vortex beam generation function; c. Mathematically superimpose the lens phase function and the spiral phase function to form a combined phase function; d. Calculate and generate pattern data for forming microstructures on the surface of the super-resolution reading lens based on the combined phase function.

[0018] Optionally, step c further includes superimposing an achromatic phase function onto the combined phase function, wherein the achromatic phase function is designed to make the first wavelength beam and the second wavelength beam confocal after passing through the super-resolution reading objective; step d further includes iteratively adjusting the parameters of the microstructure through an optimization algorithm to minimize the axial and lateral positional differences between the first wavelength beam and the second wavelength beam at the focal point.

[0019] Optionally, the micro-nano fabrication process includes at least one of optical lithography, electron beam lithography, reactive ion etching, or inductively coupled plasma etching.

[0020] This invention employs a highly integrated design concept, replacing the traditional discrete component combination scheme. Specifically, this invention integrates the focusing, spiral phase modulation, and achromatic correction functions, which originally required discrete design, into a single, planar optical element surface through micro-nano structure design, encoding and etching them uniformly. Based on this invention, firstly, focusing, spiral phase modulation, and other functions occur simultaneously on the same element surface, eliminating the need for the beam to propagate between different elements and fundamentally eliminating phase distortion caused by Fresnel diffraction and other effects; secondly, the excitation and suppression beams pass through the same integrated element, and their relative positions are precisely fixed by the microstructure on the element surface, achieving self-collimation of the optical path and significantly improving the system's stability and robustness; finally, utilizing the negative dispersion characteristics of diffractive optical elements, this invention can efficiently compensate for or eliminate the inherent dispersion of materials on a single element, without the need for complex lens groups, providing an efficient and concise achromatic correction solution. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0022] Figure 1 This is a schematic diagram illustrating the working principle of the system of the present invention.

[0023] Figure 2a This is a schematic diagram of the phase of the focusing lens.

[0024] Figure 2b This is a schematic diagram of the spiral phase.

[0025] Figure 2c The microstructure of the surface of the super-resolution reading objective lens. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] In a first aspect, the present invention provides an integrated super-resolution reading and writing objective lens, wherein the objective lens is a single diffractive optical element, the surface of the diffractive optical element has a preset microstructure, the microstructure is a binary or multi-level stepped relief structure, and the microstructure is designed to simultaneously realize at least two optical transformations on the incident light beam, including: a focusing transformation that focuses the light beam to a predetermined focal plane; and a phase modulation transformation that applies a spiral phase to the light beam to form a vortex beam.

[0028] Optionally, the microstructure is also designed to achieve a third optical transformation, including: an achromatic transformation to correct chromatic aberration, such that the excitation beam of the first wavelength and the suppression beam of the second wavelength are confocal on the predetermined focal plane; wherein the achromatic transformation is achieved by designing the microstructure so that the excitation beam of the first wavelength and the suppression beam of the second wavelength operate at different diffraction orders.

[0029] Optionally, when the excitation beam of the first wavelength is incident, the objective lens forms a dot-shaped spot with maximized central light intensity at the predetermined focal plane; when the suppression beam of the second wavelength is incident, the objective lens forms an annular spot at the predetermined focal plane, wherein the ratio of the central light intensity of the annular spot to the maximum light intensity of the annular spot is less than or equal to 0.05.

[0030] Optionally, the microstructure is formed by spatially encoding a total phase function, which is a mathematical superposition of at least one lens phase function and a spiral phase function.

[0031] Optionally, the total phase function further includes an achromatic phase function to compensate for the inherent dispersion of the diffractive optical element or the material dispersion of the substrate material.

[0032] In a second aspect, the present invention provides a system for a stimulated emission depletion super-resolution microscope, the system employing the super-resolution reading objective as described in the first aspect above as its reading objective.

[0033] Thirdly, the present invention provides an integrated method for fabricating a super-resolution reading and writing objective lens, comprising: acquiring pattern data of microstructures on the surface of the super-resolution reading and writing objective lens; and forming, in a single step, a microstructure corresponding to the pattern data on at least one surface of a provided optical substrate through micro-nano fabrication technology, so that the super-resolution reading and writing objective lens can simultaneously achieve focusing, spiral phase modulation and achromatic functions.

[0034] Optionally, pattern data of the microstructure on the surface of the super-resolution reading lens is obtained through the following steps: a. Define a target focusing function and determine a lens phase function based on the target focusing function; b. Define a target vortex beam generation function and determine a spiral phase function based on the target vortex beam generation function; c. Mathematically superimpose the lens phase function and the spiral phase function to form a combined phase function; d. Calculate and generate pattern data for forming microstructures on the surface of the super-resolution reading lens based on the combined phase function.

[0035] Optionally, step c further includes superimposing an achromatic phase function onto the combined phase function, wherein the achromatic phase function is designed to make the first wavelength beam and the second wavelength beam confocal after passing through the super-resolution reading objective; step d further includes iteratively adjusting the parameters of the microstructure through an optimization algorithm to minimize the axial and lateral positional differences between the first wavelength beam and the second wavelength beam at the focal point.

[0036] Optionally, the micro-nano fabrication process includes at least one of optical lithography, electron beam lithography, reactive ion etching, or inductively coupled plasma etching.

[0037] Specifically, the solution of the present invention is further described according to the following embodiments:

[0038] This invention illustrates the specific design method and manufacturing process of an integrated super-resolution reading / writing objective lens. This objective lens is a single binary optical element capable of achieving high-quality focusing of excitation light and achromatic vortex focusing of STED suppression light on the same substrate. Its principle is as follows: Figure 1 As shown.

[0039] The core of this invention lies in designing a total phase function φ(ρ,θ), which can be encoded as a surface relief structure of a binary optical element. This total phase function is a linear superposition of individual phase functions that achieve different optical functions.

[0040] In a polar coordinate system (ρ, θ) with the center of the component as the origin, the total phase function can be expressed as:

[0041] φ(ρ,θ)=φ lens (ρ)+φ vortex (θ)+φ achr (ρ,λ) (1)

[0042] Where: ρ is the radial coordinate, and θ is the azimuth coordinate. φ lens (ρ) is the fundamental objective focusing phase. φ vortex (θ) is the spiral phase used to generate the ring-shaped light spot. φ achr(ρ,λ) is the phase used to correct chromatic aberration; it is a function of the radial coordinate ρ and is also related to the incident light wavelength λ. The detailed derivation of each phase component is given below.

[0043] (a) Focusing phase φ lens (ρ)

[0044] An ideal thin lens introduces a phase transformation into parallel incident light, aiming to convert a plane wavefront into a converging spherical wavefront. For a lens designed with a focal length of f and an operating wavelength of λ, its phase function is:

[0045]

[0046] The design wavelength λ is usually chosen to be the wavelength λ2 of STED light.

[0047] (b) Helical phase φ vortex (θ)

[0048] To generate a vortex spot with zero central intensity at the focal point, a spiral phase needs to be introduced. This phase is only related to the azimuth angle θ, and its form is:

[0049] Φ vortex (θ)=l·θ (3)

[0050] Where l is the topological charge number, which is an integer. For the standard STED application in this embodiment, a first-order vortex beam generated by l=1 is used.

[0051] (c) Achromatic phase φ achr (ρ,λ)

[0052] The focal length of a diffractive optical element is inversely proportional to its wavelength, which leads to strong dispersion. This invention utilizes this characteristic to actively compensate for chromatic aberration. The goal of this invention is to focus the excitation light (first wavelength λ1) and the STED light (second wavelength λ2) at the same axial position f.

[0053] Preliminary derivation shows that it is impossible to separate λ1 and λ2 to achieve the same focal length for both wavelengths using only a single diffraction lens function or a surface relief design. Therefore, this invention proposes an optimized numerical method. A uniform surface relief height function h(ρ,θ) is defined, with its corresponding phase function as:

[0054]

[0055] Define a general target phase function Φ1(ρ,θ), which includes the required functions such as spiral phase modulation and achromatic modulation:

[0056]

[0057] Transform this target phase into a reference relief depth h0(ρ,θ) so that the target phase is generated when operating at the m2 order diffraction at the design wavelength λ2:

[0058]

[0059] Then, this continuous relief depth h0 is quantized to obtain the final binary or multi-level surface relief h(ρ,θ). For an N-order element, its step height is:

[0060]

[0061] Total etching depth

[0062]

[0063] By selecting diffraction orders m1 and m2 such that m1λ1≈m2λ2, the wavefront distortion of the principal diffraction order of the excitation light is minimized, while still forming a near-diffraction-limited focal point. Chromatic aberration is minimized through fine-tuning parameters and iterative optimization algorithms. The simulated phase and surface structure are shown below. Figure 2a , 2b As shown in 2c.

[0064] The final design process can be summarized as follows:

[0065] 1. Determine the working wavelengths λ1 (excitation) and λ2 (STED), as well as the target numerical aperture NA and focal length f.

[0066] 2. Select appropriate diffraction orders m1, m2 and topological charge l.

[0067] 3. Based on formula (5), construct the target phase function φ(ρ,θ) which includes focusing and vortexing functions.

[0068] 4. Calculate the corresponding continuous surface relief height h0(ρ,θ) according to formula (6).

[0069] 5. Perform a modulo H operation on h0 (H is the maximum step depth) and perform N-order quantization to generate the final surface microstructure distribution map.

[0070] 6. Import the generated microstructure model into optical design software such as Zemax to simulate and verify the focusing situation at two wavelengths. Iteratively optimize and fine-tune the parameter f to minimize the focal spot size and residual chromatic aberration.

[0071] Manufacturing process flow:

[0072] The integrated super-resolution reading objective lens in this embodiment is manufactured using standard micro / nano fabrication processes. It is designed to fabricate an 8th-order diffraction optical element on a fused silica substrate, and the specific process is as follows:

[0073] 1. Substrate preparation: Select double-sided polished UV-grade fused silica wafers, clean and dry them.

[0074] 2. Photoresist coating: A layer of positive photoresist is uniformly coated on the substrate surface by spin coating.

[0075] 3. Mask generation and photolithography:

[0076] • Decompose the N-order quantized microstructure diagram designed in the previous step into log2(N) binary masks. For an 8-order device, 3 masks are required.

[0077] • First Exposure and Etching: Using a first mask, the pattern is exposed onto the photoresist using ultraviolet lithography. After development, a structure with a depth of H / 2 is etched onto the quartz substrate using reactive ion etching (RIE) or inductively coupled plasma (ICP) etching techniques. The remaining photoresist is then removed.

[0078] • Second exposure and etching: Recoat the photoresist, use a second mask, and repeat the exposure, development, and etching process. This time, the etching depth is H / 4.

[0079] • Third exposure and etching: Similarly, use a third mask with an etching depth of H / 8.

[0080] • By performing three engravings, a microstructure with eight different step heights can be formed on the substrate surface.

[0081] 4. Inspection: Use an atomic force microscope or profilometer to measure the etching depth and surface morphology to ensure that they are consistent with the design values.

[0082] 5. Anti-reflection coating: An anti-reflection coating for the working wavelength band (λ1 and λ2) is coated on both surfaces of the diffractive optical element to reduce reflection loss and improve optical efficiency.

[0083] In summary, this invention integrates the focusing, spiral phase modulation, and achromatic correction functions—which originally required separate designs—into a single, planar optical element surface through micro / nano structure design, uniformly encoding and etching them. First, the focusing and spiral phase modulation functions occur simultaneously on the same element surface, eliminating the need for beam propagation between different elements and fundamentally eliminating phase distortion caused by Fresnel diffraction and other effects. Second, the excitation and suppression beams pass through the same integrated element, and their relative positions are precisely fixed by the microstructure on the element surface, achieving self-collimation of the optical path and significantly improving the system's stability and robustness. Finally, utilizing the negative dispersion characteristics of diffractive optical elements, this invention can efficiently compensate for or eliminate inherent material dispersion on a single element, eliminating the need for complex lens assemblies and providing an efficient and concise achromatic correction solution.

[0084] Specific embodiments of the invention have now been described. Other embodiments are within the scope of the appended claims. In some cases, the actions described in the claims can be performed in a different order and still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require a specific or sequential order to achieve the desired result. In some embodiments, multitasking and parallel processing can be advantageous.

[0085] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the embodiments of the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the embodiments of the present invention, and the patent protection scope of the embodiments of the present invention should be defined by the claims.

Claims

1. An integrated super-resolution reading and writing objective lens, characterized in that, The objective lens is a single diffractive optical element, and the surface of the diffractive optical element has a predetermined microstructure. The microstructure is a binary or multi-level stepped relief structure, and the microstructure is designed to simultaneously achieve at least two optical transformations on the incident beam, including: Focusing transformation that focuses a beam of light onto a predetermined focal plane; Phase modulation transformation that applies a spiral phase to a beam to form a vortex beam.

2. The super-resolution reading / writing objective lens according to claim 1, characterized in that, The microstructure is also designed to achieve a third type of optical transformation, including: Achromatic transformation to correct chromatic aberration, so that the excitation beam of the first wavelength and the suppression beam of the second wavelength are confocal on the predetermined focal plane; The achromatic transformation is achieved by designing the microstructure so that the excitation beam of the first wavelength and the suppression beam of the second wavelength operate at different diffraction orders.

3. The super-resolution reading / writing objective lens according to claim 2, characterized in that, When the excitation beam of the first wavelength is incident, the objective lens forms a dot-shaped light spot with maximized central light intensity at the predetermined focal plane; when the suppression beam of the second wavelength is incident, the objective lens forms an annular light spot at the predetermined focal plane, wherein the ratio of the central light intensity of the annular light spot to the maximum light intensity of the annular light spot is less than or equal to 0.

05.

4. The super-resolution reading objective lens according to any one of claims 1 to 3, characterized in that, The microstructure is formed by spatially encoding a total phase function, which is a mathematical superposition of at least one lens phase function and a spiral phase function.

5. The super-resolution reading / writing objective lens according to claim 4, characterized in that, The total phase function also includes an achromatic phase function to compensate for the inherent dispersion of the diffractive optical element or the material dispersion of the substrate material.

6. A system for stimulated emission depletion super-resolution microscopy, characterized in that, The system uses the super-resolution read / write objective lens as described in any one of claims 1 to 5 as its read / write objective lens.

7. A method for fabricating an integrated super-resolution reading and writing objective lens, characterized in that, include: Acquire pattern data of the surface microstructure of a super-resolution reading objective lens; Through micro-nano fabrication technology, a microstructure corresponding to the pattern data is formed on at least one surface of a provided optical substrate in one step, enabling the super-resolution reading objective lens to simultaneously achieve focusing, spiral phase modulation, and achromatic functions.

8. The method according to claim 7, characterized in that, The following steps were used to obtain pattern data of the surface microstructure of the super-resolution reading objective lens: a. Define a target focusing function, and determine a lens phase function based on the target focusing function; b. Define a target vortex beam generation function, and determine a spiral phase function based on the target vortex beam generation function; c. The lens phase function and the spiral phase function are mathematically superimposed to form a combined phase function; d. Based on the combined phase function, calculate and generate pattern data for forming microstructures on the surface of the super-resolution reading objective.

9. The method according to claim 8, characterized in that, Step c further includes superimposing an achromatic phase function onto the combined phase function, wherein the achromatic phase function is designed to make the first wavelength beam and the second wavelength beam confocal after passing through the super-resolution reading objective; step d further includes iteratively adjusting the parameters of the microstructure through an optimization algorithm to minimize the axial and lateral positional differences between the first wavelength beam and the second wavelength beam at the focal point.

10. The method according to claim 7, characterized in that, The micro-nano fabrication process includes at least one of optical lithography, electron beam lithography, reactive ion etching, or inductively coupled plasma etching.

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