Methods for generating supercritical focused light fields and supercritical focusing optical heads

Abstract

This application relates to the field of laser modulation, providing a method for generating a supercritical focused optical field, a supercritical focusing optical head, and a method for determining modulation parameters. The supercritical focusing optical head includes a light source and a spatial light modulator. The method for generating a supercritical focused optical field includes: the light source generating incident light; and the spatial light modulator modulating the phase of the incident light to generate a focused optical field that satisfies supercritical conditions. The entrance pupil surface of the spatial light modulator includes N ring zones, each corresponding to one of N sets of modulation parameters, which are obtained based on supercritical conditions. This method utilizes phase modulation between adjacent ring zones, allowing the width and phase of each ring zone to be iteratively optimized and adjusted based on supercritical conditions. This reduces sidelobe energy and increases main lobe energy while maintaining the main lobe size above the diffraction limit, making it suitable for high-density optical storage and laser processing.

Description

Technical Field

[0001] This application relates to the field of laser modulation, and more specifically, to a method for generating a supercritical focused optical field, a supercritical focusing optical head, and a method for determining modulation parameters. Background Technology

[0002] In fields such as optical storage and laser processing, lenses are used to focus light beams into a spot, which is then used for operations such as information recording or material processing. Therefore, the smaller the size of the focused spot, the more information can be carried per unit area, thereby increasing the capacity of optical storage and the precision of laser processing.

[0003] However, due to the wave nature of light, its imaging resolution is limited by the diffraction limit. According to Rayleigh's criterion for physical two-point resolution under incoherent imaging conditions, the size of the focused spot is limited by the incident light wavelength and the numerical aperture of the optical system. The minimum full width at half maximum (FWHM) of the focused spot achievable under the diffraction limit is 0.61λ / NA, where λ is the incident light wavelength and NA is the numerical aperture of the optical system. While using shorter wavelength incident light or immersion lens systems with higher numerical apertures can improve the focusing ability of the optical system to some extent, it limits the application of the optical system in practical fields such as optical storage or laser processing. Therefore, how to generate a focused spot exceeding the diffraction limit that can be applied in optical storage or laser processing has become an urgent technical problem to be solved. Summary of the Invention

[0004] This application provides a method for generating a supercritical focused optical field, a supercritical focusing optical head, and a method for determining modulation parameters. The generated focused optical field can meet the supercritical condition, with the size of the focused spot being smaller than the diffraction limit of the optical system and the intensity of the main lobe at the focal point being higher than that of other side lobes. This enables the focused optical field that exceeds the diffraction limit to be applied to fields such as optical storage or laser processing, thereby improving the capacity of optical storage and the precision of laser processing.

[0005] Firstly, a method for generating a supercritical focused optical field is provided. This method is applied to a supercritical focusing optical head, which includes a light source and a spatial light modulator. The method includes: the light source generating incident light; and the spatial light modulator modulating the phase of the incident light to generate a focused optical field satisfying a supercritical condition. The entrance pupil surface of the spatial light modulator includes N rings, each ring corresponding to one of N sets of modulation parameters. Each of the N sets of modulation parameters includes a ring width and a modulation phase. Each of the N rings modulates the phase of the incident light under the corresponding modulation parameters to generate diffracted light. The diffracted light generated by the N rings is coherent, causing the focused optical field to satisfy the supercritical condition. N is a positive integer greater than 1. The N sets of modulation parameters are obtained based on the supercritical condition, which includes that the intensity of the focused optical field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused optical field generated by the spatial light modulator at the focal point, and that the radius of the focal spot of the focused optical field generated by the spatial light modulator at the focal point satisfies the following conditions:

[0006]

[0007] Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head.

[0008] According to the technical solution provided in this application, by utilizing phase modulation between adjacent rings, the spatial size of the central focal point is coherently squeezed, so that the width and phase of each ring can be iteratively optimized and adjusted based on supercritical conditions. This allows the focused light field generated under the final determined width and phase of each ring to meet supercritical conditions, that is, while maintaining the main lobe size to break through the diffraction limit, the side lobe energy is reduced and the main lobe energy is increased, making it suitable for high-density optical storage and laser processing.

[0009] In conjunction with the first aspect, in some implementations of the first aspect, the supercritical focusing optical head further includes a cyclopolarizer, and a spatial light modulator modulates the phase of the incident light to generate a focused optical field that satisfies the supercritical condition. This includes: the spatial light modulator modulates the phase of the incident light to generate the focused optical field, wherein each of the N rings is divided into a first part and a second part, the boundary between the first part and the second part of each of the N rings is a straight line passing through the center of the entrance pupil plane, and the modulation phase in each of the N sets of modulation parameters includes a first modulation phase and a second modulation phase, the first part corresponding to the first modulation phase, the second part corresponding to the second modulation phase, and the phase difference between the first modulation phase and the second modulation phase being π; the cyclopolarizer converts the focused optical field so that the focused optical field satisfies the supercritical condition, which also includes that the polarization orientation purity of the focused optical field generated by the spatial light modulator at the focal point is greater than 90%, and the polarization orientation is in the same direction as the boundary line.

[0010] According to the above technical solution, by further dividing the ring into two semicircular parts and superimposing a stepped phase with a phase difference of π on each part, phase modulation of the 0 / π stepped phase is achieved. Based on the supercritical focused light field, vector modulation of the focused light field is realized, which can generate a high-purity transversely linearly polarized focused light spot that breaks through the diffraction limit and whose polarization direction is arbitrarily controllable, thereby expanding the dimensions of high-density optical storage and laser processing.

[0011] In conjunction with the first aspect, in certain implementations of the first aspect, the spatial light modulator modulates the phase of the incident light to generate a focused light field that satisfies the supercritical condition, including: the spatial light modulator modulates the phase of the incident light, wherein the modulation phase in each of the N sets of modulation parameters further includes a grating shift phase, the grating shift phase causing each of the N ring zones to modulate the phase of the incident light to generate M beams of diffracted light in different directions, and each of the N ring zones generating the Mth beam... n The diffracted beams coherently converge at the focal plane to produce a focal point, such that the focused light field has M focal points at different positions on the focal plane, each of the M focal points satisfying the supercritical condition, where M is a positive integer greater than 1. n It is a positive integer less than or equal to M.

[0012] According to the above technical solution, by further superimposing grating displacement phase modulation on each ring, the focused spot is moved off-axis, thereby realizing arbitrary control of the spatial position of the focused spot. Furthermore, multiple focal points at different positions exist in the focal plane of the focused light field, which can generate a multi-focal focused spot that breaks through the diffraction limit, thereby improving the efficiency of high-density optical storage and laser processing.

[0013] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: determining N sets of initial modulation parameters corresponding one-to-one with the N ring bands, each set of initial modulation parameters including an initial ring band width and an initial modulation phase; determining an initial intensity distribution, which is the intensity distribution of the focused light field generated by the spatial light modulator under the N sets of initial modulation parameters; adjusting the N sets of initial modulation parameters according to the initial intensity distribution and the supercritical condition, so that the intensity distribution of the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the supercritical condition; and determining the value of the N sets of modulation parameters as the value of the adjusted N sets of initial modulation parameters.

[0014] According to the above technical solution, by first setting the initial value of the modulation parameters, the intensity distribution of the focused light field under the initial modulation parameters can be obtained. Then, according to the intensity distribution of the desired focused light field, the supercritical condition is set. Thus, the modulation parameters of the spatial light modulator can be continuously adjusted iteratively according to the optimization algorithm, and the complex modulation parameters can be gradually determined so that the focused light field generated under the finally determined modulation parameters can meet the supercritical condition, generating a supercritical focused light field that exceeds the diffraction limit and can be applied to fields such as optical storage or laser processing.

[0015] Secondly, a supercritical focusing optical head is provided, comprising: a light source for generating incident light; and a spatial light modulator for modulating the phase of the incident light to generate a focused light field satisfying supercritical conditions. The entrance pupil surface of the spatial light modulator includes N annular bands, each corresponding to one of N sets of modulation parameters. Each of the N sets of modulation parameters includes an annular band width and a modulation phase. Each of the N annular bands modulates the phase of the incident light under the corresponding modulation parameters to generate diffracted light. The coherence of the diffracted light generated by the N annular bands ensures that the focused light field satisfies the supercritical conditions. N is a positive integer greater than 1. The N sets of modulation parameters are obtained based on the supercritical conditions, which include that the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, and that the full width at half maximum (FWHM) of the focal spot of the focused light field generated by the spatial light modulator at the focal point satisfies:

[0016]

[0017] Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head.

[0018] In conjunction with the second aspect, in some implementations of the second aspect, a spatial light modulator is used to: modulate the phase of the incident light to generate a focused light field, wherein each of the N rings is divided into a first part and a second part, the boundary between the first part and the second part of each of the N rings is a straight line passing through the center of the entrance pupil, the modulation phase in each of the N sets of modulation parameters includes a first modulation phase and a second modulation phase, the first part corresponds to the first modulation phase, the second part corresponds to the second modulation phase, and the phase difference between the first modulation phase and the second modulation phase is π; the supercritical focusing head also includes a rotation polarization converter used to: convert the focused light field so that the focused light field satisfies the supercritical condition, the supercritical condition also includes that the polarization orientation purity of the focused light field generated by the spatial light modulator at the focal point is greater than 90%, and the polarization orientation is in the same direction as the boundary line.

[0019] In conjunction with the second aspect, in some implementations of the second aspect, a spatial light modulator is used to: modulate the phase of incident light, wherein the modulation phase in each of the N sets of modulation parameters includes a grating shift phase, the grating shift phase causing each of the N ring bands to modulate the phase of the incident light to generate M beams of diffracted light in different directions, and each of the N ring bands generating the Mth beam... n The diffracted beams coherently converge at the focal plane to produce a focal point, such that the focused light field has M focal points at different positions on the focal plane, each of the M focal points satisfying the supercritical condition, where M is a positive integer greater than 1. n It is a positive integer less than or equal to M.

[0020] Thirdly, a method for determining modulation parameters is provided. This method is applied to a spatial light modulator, the entrance pupil of which includes N annular bands. The spatial light modulator is used to modulate the phase of incident light to generate a focused light field. The N annular bands correspond one-to-one with N sets of modulation parameters. Each set of modulation parameters includes an annular band width and a modulation phase, where N is a positive integer greater than 1. The method includes: determining N sets of initial modulation parameters corresponding one-to-one with the N annular bands, where each set of initial modulation parameters includes an initial annular band width and an initial modulation phase; determining initial... The intensity distribution, specifically the initial intensity distribution, is the intensity distribution of the focused light field generated by the spatial light modulator under N sets of initial modulation parameters. Based on the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted so that the intensity distribution of the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the supercritical condition. The supercritical condition includes that the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, and that the full width at half maximum (FWHM) of the focal spot generated by the spatial light modulator at the focal point satisfies:

[0021]

[0022] Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head; the values ​​of the N sets of modulation parameters are determined to be the adjusted values ​​of the N sets of initial modulation parameters.

[0023] In conjunction with the third aspect, in some implementations of the third aspect, each of the N ring bands is divided into a first part and a second part. The boundary between the first part and the second part of each of the N ring bands is a straight line passing through the center of the entrance pupil plane. Determining N sets of initial modulation parameters corresponding one-to-one with the N ring bands includes: determining N sets of initial modulation parameters corresponding one-to-one with the N ring bands, wherein the initial modulation phase in each of the N sets of initial modulation parameters includes a first initial modulation phase and a second initial modulation phase, and the first part of each of the N ring bands corresponds to the first initial modulation phase. The second part of each of the N rings corresponds to the second initial modulation phase, and the phase difference between the first initial modulation phase and the second initial modulation phase is π. According to the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted, including: according to the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted so that the intensity distribution of the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the supercritical condition. The supercritical condition also includes that the polarization orientation purity of the focused light field generated by the spatial light modulator at the focal point is greater than 90%, and the polarization orientation is in the same direction as the boundary line.

[0024] In conjunction with the third aspect, in some implementations of the third aspect, determining N sets of initial modulation parameters corresponding one-to-one with the N ring zones includes: determining N sets of initial modulation parameters corresponding one-to-one with the N ring zones, wherein the initial modulation phase in each of the N sets of initial modulation parameters also includes a grating shift phase, the grating shift phase causing each of the N ring zones to modulate the phase of the incident light to generate M beams of diffracted light in different directions, and the Mth beam generated by each of the N ring zones... n The diffracted beams coherently converge at the focal plane to produce a focal point, such that the focused light field has M focal points at different positions on the focal plane, where M is a positive integer greater than 1. n It is a positive integer less than or equal to M; the supercritical condition includes M sets of sub-conditions corresponding one-to-one with the M focal points of the focused light field. Based on the initial intensity distribution and the supercritical condition, N sets of initial modulation parameters are adjusted, including: based on the initial intensity distribution and the supercritical condition, N sets of initial modulation parameters are adjusted so that each of the M focal points in the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the corresponding sub-condition.

[0025] In conjunction with the third aspect, in some implementations of the third aspect, N sets of initial modulation parameters are adjusted according to the initial intensity distribution and supercritical conditions, including: adjusting N sets of initial modulation parameters according to the initial intensity distribution and supercritical conditions based on genetic algorithms and / or particle swarm optimization algorithms.

[0026] Fourthly, an optical storage system is provided, including at least one supercritical focusing optical head, which is used to perform the method in the first aspect or any possible implementation of the first aspect. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart illustrating a method for generating a supercritical focused light field according to an embodiment of this application.

[0028] Figure 2 This is a schematic flowchart of a method for determining modulation parameters provided in an embodiment of this application.

[0029] Figure 3 This is a result diagram of a fluorescence reading verification experiment.

[0030] Figure 4 This is another experimental result figure from the fluorescence reading verification experiment.

[0031] Figure 5 An experimental result diagram of a super-resolution recording effect experiment.

[0032] Figure 6 Another experimental result of the super-resolution recording effect experiment.

[0033] Figure 7 This is an experimental result diagram of a PMMA polymer material dot storage experiment.

[0034] Figure 8 This is another experimental result diagram of the PMMA polymer material dot storage experiment.

[0035] Figure 9 This is an experimental result diagram of a point-by-point verification experiment on PMMA polymer material with a dot pitch of 500*500nm.

[0036] Figure 10 This is another experimental result of the point-by-point verification experiment of PMMA polymer material with a dot pitch of 500*500nm.

[0037] Figure 11 This is an experimental result diagram of a point-by-point verification experiment on PMMA polymer material with a dot pitch of 400*400nm.

[0038] Figure 12 This is another experimental result of the point-by-point verification experiment of PMMA polymer material with a dot pitch of 400*400nm.

[0039] Figure 13 This is a demonstration diagram showing the effect of applying a supercritical focused light field to parallel storage, as provided in an embodiment of this application.

[0040] Figure 14 This is another demonstration diagram showing the effect of applying the supercritical focused light field provided in the embodiments of this application to parallel storage.

[0041] Figure 15 This is another demonstration diagram showing the effect of applying the supercritical focused light field provided in the embodiments of this application to parallel storage.

[0042] Figure 16 This is a schematic structural block diagram of a supercritical focusing optical head provided in an embodiment of this application. Detailed Implementation

[0043] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0044] This application will present various aspects, embodiments, or features relating to systems comprising multiple devices, components, modules, etc. It should be understood and appreciated that individual systems may include additional devices, components, modules, etc., and / or may not include all devices, components, modules, etc. discussed in conjunction with the accompanying drawings. Furthermore, combinations of these approaches are also possible.

[0045] Furthermore, in the embodiments of this application, the words "exemplary," "for example," etc., are used to indicate that they are examples, illustrations, or descriptions. Any embodiment or design scheme described as "exemplary" in this application should not be construed as being more preferred or advantageous than other embodiments or design schemes. Specifically, the use of the term "exemplary" is intended to present the concept in a concrete manner.

[0046] In the embodiments of this application, "corresponding" and "corresponding" can sometimes be used interchangeably. It should be noted that when the distinction is not emphasized, their intended meanings are consistent.

[0047] The optical system architecture and business scenarios described in the embodiments of this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided in the embodiments of this application. As those skilled in the art will know, with the evolution of optical system architecture and the emergence of new business scenarios, the technical solutions provided in the embodiments of this application are also applicable to similar technical problems.

[0048] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0049] In this application, "at least one" means one or more, and "more than one" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A alone, A and B simultaneously, and B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0050] To facilitate understanding, the relevant terms and concepts that may be involved in the embodiments of this application will be introduced below.

[0051] 1. Rayleigh Criterion: Due to the wave nature of light, its imaging resolution is limited by the diffraction limit. In 1896, Rayleigh proposed the Rayleigh criterion for the physical resolution of two points under incoherent imaging conditions, namely, the minimum distance between two resolvable points in a microscopic imaging system is equal to the radius of the Airy disk focused by the optical system. In the field of optical focusing, according to the Rayleigh criterion, the size of the focused spot is also limited by the incident light wavelength and the numerical aperture of the optical system. The minimum full width at half maximum (FWHM) of the focused spot achievable under the diffraction limit is 0.61λ / NA, where λ is the incident light wavelength and NA is the numerical aperture of the optical system.

[0052] With the continuous development of science and technology, various fields such as biology, materials science, and precision manufacturing are placing increasingly higher demands on the size of focused light spots. Research has found that by precisely modulating the interference phenomenon of the incident light field using specially designed optical micro / nano structures, optically focused focal spots exceeding the diffraction limit can be achieved in the far field. This phenomenon is named optical super-oscillation. The physical property of optical super-oscillation originates from the superposition of multiple light fields with lower spatial frequencies. Under the modulation of constructive interference or destructive interference, a localized rapidly oscillating light field is formed. This localized oscillation frequency can be much higher than the highest spatial frequency of the light field, thus forming a focused light spot with a minimum feature size smaller than the optical diffraction limit in the local space.

[0053] 2. Super-oscillation Criterion: While optical super-oscillation can generate a focused spot exceeding the diffraction limit locally within the focused optical field, this method exhibits a strong sidelobe effect, where the optical energy is squeezed into the sidelobe space. Consequently, sidelobes with higher intensity than the main lobe are generated next to the main lobe exceeding the diffraction limit. The smaller the focused size of the main lobe, the higher the intensity of the sidelobes, reaching several orders of magnitude higher than the main lobe. These sidelobes cannot be eliminated and strongly interfere with the main lobe. Therefore, the focused spot exceeding the diffraction limit generated by this method cannot be practically applied to fields such as optical storage or laser processing.

[0054] Therefore, through further research, the concept of the super-oscillation criterion was theoretically proposed. The super-oscillation criterion is defined as 0.38λ / NA, which, together with the Rayleigh criterion's 0.61λ / NA, divides the range of optical focusing focal spot sizes into three parts. Focusing focal spots with a full width at half maximum (FWHM) smaller than the super-oscillation criterion exhibit optical super-oscillation, theoretically allowing for infinitely small focusing focal spots. However, the intensity of their side lobes increases exponentially with decreasing main lobe size, while the energy utilization efficiency of the incident light decreases sharply, significantly impacting practical applications. Focusing focal spots with a FWHM larger than the Rayleigh criterion, while having negligible side lobe effects, cannot achieve super-diffraction-limited modulation effects. Only focusing focal spots with a FWHM between the super-oscillation criterion and the Rayleigh criterion can achieve super-diffraction-limited focusing while effectively suppressing side lobe effects. Their depth of focus can also be flexibly designed as needed, providing great convenience for practical applications.

[0055] 3. Supercritical Lens (SCL): An SCL is defined as a focusing lens whose focal spot lateral dimension lies between the superoscillation criterion and the Rayleigh criterion. Traditional optical lenses focus light by utilizing the refraction phenomenon at the interface between two media with different refractive indices. By adjusting the lens curvature, the focusing effect of the propagation field can be controlled. Diffractive optical elements essentially work by modulating the light field intensity and phase distribution of each diffractive secondary source on the designed focal spot plane to achieve the designed optical effect. An SCL is essentially also an optimized diffractive optical element; its focusing characteristics can be fully optimized by using various diffraction theories and optimization algorithms to design and optimize the parameters of the position and width of each concentric ring. The light field generated by SCL modulation is called the supercritical focusing light field.

[0056] 4. Spatial Light Modulator (SLM): A spatial light modulator is a dynamic device that can change the amplitude, polarization, and phase of incident light under the control of an external signal. It features easy operation, easy integration, low loss, and high refresh rate. Common SLMs include digital micromirror devices (DMDs) for amplitude adjustment and liquid crystal LCMs (LC-SLMs) for phase modulation. DMDs are widely used spatial light modulators that modulate the amplitude of incident light. Each pixel is an independently controllable micromirror; by switching the direction of each micromirror, the angle of the outgoing light can be controlled per pixel. DMDs offer advantages such as fast switching speed and ease of control. Each pixel unit of an LC-SLM is composed of liquid crystal molecules. Liquid crystals are widely used in spatial light modulators due to their birefringence.

[0057] Because spatial light modulators can controllably modulate the phase of the incident light field, they can achieve phase modulation of SCL (Sequential Light Chromatography) by designing appropriate modulation parameters. Furthermore, spatial light modulators can also achieve various spatial light phase modulation methods, such as stepped phase modulation and grating-shifted phase modulation.

[0058] In fields such as optical storage and laser processing, lenses are used to focus light beams into a spot, which is then used for operations such as information recording or material processing. Therefore, the smaller the size of the focused spot, the more information can be carried per unit area, resulting in a higher information density or energy density, thereby increasing the capacity of optical storage and the precision of laser processing.

[0059] While using shorter wavelength incident light or immersion lens systems with higher numerical apertures can improve the focusing ability of optical systems to some extent, they still cannot overcome the diffraction limit to achieve the desired focused spot size, thus limiting the upper limit of the optical system. Traditional methods introduce superoscillatory behavior from quantum mechanics into optical field focusing, incorporating rapidly oscillating superoscillatory functions into the optical field modulation. This allows the rapid oscillations at local spatial locations within the focal field to exceed the fastest Fourier spatial frequency under diffraction-limited focusing, thereby achieving local focusing that breaks the diffraction limit. However, the optical superoscillations achieved through band-limited functions exhibit strong sidelobe effects, hindering their application in fields such as optical storage and laser processing. Therefore, generating a focused spot exceeding the diffraction limit applicable to optical storage or laser processing has become a pressing technical problem.

[0060] Therefore, a method for generating a supercritical focused optical field is provided, which is applied to a supercritical focusing optical head, comprising a light source and a spatial light modulator. By setting multiple rings on the entrance pupil surface of the spatial light modulator, the width and modulation phase of each ring are optimized and determined according to a set supercritical condition. By utilizing phase modulation between adjacent rings, the spatial size of the central focal point is coherently compressed, so that the generated focused optical field satisfies the supercritical condition. The size of the focused spot is smaller than the diffraction limit of the optical system, and the intensity of the main lobe at the focal point is higher than that of other side lobes. Thus, a focused optical field exceeding the diffraction limit can be applied to fields such as optical storage or laser processing, improving the capacity of optical storage and the precision of laser processing.

[0061] The following is combined Figure 1 This application describes in detail the method for generating a supercritical focused light field. For example... Figure 1 As shown, the method includes the following steps.

[0062] S110: The light source produces incident light.

[0063] For example, in step S110, the light source in the supercritical focusing optical head generates incident light that satisfies the incident conditions of the spatial light modulator. As an example, and not a limitation, the incident conditions of the spatial light modulator may include, but are not limited to, at least one of the wavelength, phase, and polarization state of the incident light. For instance, in the field of optical storage, Blu-ray digital video discs (DVDs) use a blue laser with a wavelength of 405 nm for writing, so the incident light wavelength generated by the light source can be 405 nm; solid-state laser cutting uses a wavelength of 1064 nm, so the incident light wavelength generated by the light source can be 1064 nm. As another example, spatial light modulators generally only respond to linearly polarized states in a specific direction, so the incident light generated by the light source can be linearly polarized, and the polarization direction is a specific polarization state that the spatial light modulator can respond to.

[0064] Alternatively, the light source can be a laser generator.

[0065] S120: The spatial light modulator modulates the phase of the incident light to generate a focused light field that satisfies the supercritical condition.

[0066] For example, in step S120, the spatial light modulator decomposes the entrance pupil plane into N rings, each ring having a specific modulation parameter. Each of the N rings is used to modulate the phase of the incident light under the corresponding modulation parameter to generate diffracted light, thereby enabling the diffracted light generated by the N rings to coherently form a focused light field that satisfies the supercritical condition.

[0067] In this spatial light modulator, the entrance pupil is circular, and the ring bands are a series of concentric rings. The number N of ring bands on the entrance pupil is a positive integer greater than 1. A larger number of ring bands results in finer modulation, but this is controlled by the size of the phase modulation region of the spatial light modulator, and therefore can be appropriately selected based on the size of the phase modulation region. Optionally, N can be 60.

[0068] The modulation parameters for each annular band include, but are not limited to, the band width and modulation phase. The band width is the difference between the outer and inner radii of the annulus, and the modulation phase is the change in phase of the incident light after passing through the annulus. There are N annular bands corresponding one-to-one with N sets of modulation parameters, with each annulus corresponding to one set of parameters. The values ​​of the modulation parameters corresponding to different annular bands can be the same or different. The N sets of modulation parameters are obtained based on supercritical conditions. The specific method for determining the modulation parameters will be explained in detail below and will not be repeated here.

[0069] The supercritical condition is a condition that the focused light field generated by the spatial light modulator must satisfy when determining the modulation parameters. For the focused light field in this application embodiment that exceeds the diffraction limit and can be applied to optical storage or laser processing, the supercritical condition includes at least the following: the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, and the full width at half maximum (FWHM) of the focal spot of the focused light field generated by the spatial light modulator at the focal point satisfies:

[0070]

[0071] Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head. It should be understood that since the numerical aperture of the supercritical focusing head is actually determined by the numerical aperture of the focusing objective lens included within it, in some possible implementations, NA can also be referred to as the numerical aperture of the focusing objective lens in the supercritical focusing head, or simply as the numerical aperture of the focusing objective lens.

[0072] The technical solution of this application embodiment utilizes phase modulation between adjacent rings to coherently compress the spatial size of the central focal point, enabling the width and phase of each ring to be iteratively optimized and adjusted based on supercritical conditions. This allows the focused light field generated under the final determined width and phase of each ring to meet supercritical conditions, i.e., while maintaining the main lobe size to break through the diffraction limit, reducing the side lobe energy and increasing the main lobe energy, making it suitable for high-density optical storage and laser processing.

[0073] The following is combined Figure 2 The method for determining modulation parameters in the embodiments of this application is described in detail. Optionally, Figure 2 The method shown can be implemented alone or in combination with... Figure 1 The method shown is combined with, when with Figure 1 When the methods shown are combined, Figure 2 The method shown is executed and Figure 1 Before the method shown.

[0074] like Figure 2 As shown, the method includes the following steps.

[0075] S210: Determine the N sets of initial modulation parameters that correspond one-to-one with the N ring bands.

[0076] For example, in step S210, initial modulation parameters can be set for each of the N ring bands. Specifically, N sets of initial modulation parameters are set for each of the N ring bands, each set of initial modulation parameters including at least an initial ring band width and an initial modulation phase. The initial ring band width is the initial width set for the ring band, and the modulation phase is the initial phase modulation amount set for the ring band. Optionally, the N sets of initial modulation parameters can be set to arbitrary values, and the values ​​of the initial modulation parameters corresponding to different ring bands can be the same or different.

[0077] S220: Determine the initial intensity distribution.

[0078] For example, in step S220, the intensity distribution of the focused light field generated by the spatial light modulator under N sets of initial modulation parameters can be determined; this intensity distribution is called the initial intensity distribution. Specifically, the initial intensity distribution of the focused light field can be solved by integrating the aperture function of the entrance pupil of the spatial light modulator under the initial modulation parameters. For example, the initial intensity distribution can be calculated based on the vector Rayleigh-Sommerfeld diffraction theory and / or the vector Debye diffraction integral theory, thereby fully considering the vector characteristics of the incident light field with different polarization states and more accurately describing the amplitude, phase, and polarization state of the focused light field.

[0079] It should be understood that determining the initial distribution intensity of the focused light field through the aperture function can more accurately and conveniently determine the initial distribution intensity through theoretical calculation. However, the technical solution of this application is not limited to this. For example, when the initial modulation parameters of the spatial light modulator can be easily adjusted, the initial intensity distribution can also be determined by measurement or other methods. This application does not make specific limitations on this.

[0080] S230: Adjust N sets of initial modulation parameters according to the initial intensity distribution and supercritical conditions.

[0081] For example, in step S230, the initial distribution intensity determined in S220 can be compared with the preset supercritical conditions, and the N sets of initial modulation parameters can be adjusted by an optimization algorithm based on the comparison results.

[0082] The supercritical condition is preset based on the characteristics of the focused light field ultimately obtained by the spatial light modulator. In other words, it is a preset condition that the final modulation parameters determined after adjustment must satisfy during the initial modulation parameter adjustment process. For example, to obtain a focused light field exceeding the diffraction limit that can be applied to optical storage or laser processing, the supercritical condition can be set as follows: the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, as described in S120 above, and the full width at half maximum (FWHM) of the focal spot of the focused light field generated by the spatial light modulator at the focal point satisfies:

[0083]

[0084] Depending on actual usage requirements, the specific values ​​of the supercritical conditions can be arbitrarily set within the above range, and this application does not impose any specific limitations on them. As an example rather than a limitation, the normalized intensity of the focused light field at the focal point can be set to 1, and the normalized intensity at any other position on the entire optical axis except the focal point can be less than 0.3, to describe the requirement that the main lobe intensity is higher than the side lobes; and the full width at half maximum (FWHM) of the point spread function of the focal spot can be set to a value less than 0.61λ / NA and greater than or equal to 0.38λ / NA, for example, 0.38λ / NA, to describe that the focal spot size exceeds the diffraction limit.

[0085] Optimization algorithms include, but are not limited to, particle swarm optimization (PSO) and genetic algorithms (GA). PSO, a type of evolutionary algorithm similar to simulated annealing, starts with random solutions and iteratively searches for the optimal solution, evaluating its quality by comparing it to a pre-defined objective function. GA is a computational model simulating the biological evolutionary process based on Darwin's theory of evolutionary natural selection and genetic mechanisms. It searches for the optimal solution by simulating natural evolution, using mathematical methods and computer simulation to transform the problem-solving process into processes similar to crossover and mutation of chromosomes and genes in biological evolution. The results determined by these optimization algorithms are highly accurate and converge quickly, enabling rapid and accurate adjustment of initial modulation parameters. However, these algorithms cannot reveal the intrinsic physical properties of the structure, thus failing to clearly describe the role and contribution of each ring on the focal plane.

[0086] S240: Determine the values ​​of the N sets of modulation parameters as the adjusted values ​​of the N sets of initial modulation parameters.

[0087] For example, in step S240, the values ​​of the N initial modulation parameters finally obtained after adjustment according to the optimization algorithm can be used as the N modulation parameters of the spatial light modulator in the supercritical focusing optical head. Specifically, the process of adjusting the initial modulation parameters according to the optimization algorithm is to repeat the above steps S220 and S230 multiple times. After each adjustment, the initial intensity distribution is re-determined, and the initial modulation parameters are further adjusted based on the comparison result between the newly determined initial intensity distribution and the supercritical condition, until the focused light field generated by the spatial light modulator under the adjusted initial modulation parameters meets the preset supercritical condition. The adjusted initial modulation parameters are then used as the modulation parameters of the spatial light modulator in the supercritical focusing optical head used to generate the supercritical focused light field.

[0088] By using the technical solution of this application embodiment, by first setting the initial value of the modulation parameters, the intensity distribution of the focused light field under the initial modulation parameters can be obtained. Then, according to the intensity distribution of the focused light field to be finally achieved, the supercritical condition is set. In this way, the modulation parameters of the spatial light modulator can be continuously adjusted iteratively according to the optimization algorithm, and the complex modulation parameters can be gradually determined so that the focused light field generated under the finally determined modulation parameters can meet the supercritical condition, and generate a supercritical focused light field that exceeds the diffraction limit and can be applied to fields such as optical storage or laser processing.

[0089] For step S120 above, in order to meet a wider range of applications in optical storage or laser processing, more conditions can be added to the supercritical conditions to generate more diverse focused light fields that satisfy the supercritical conditions. A detailed explanation is provided below with reference to specific embodiments.

[0090] In some possible implementations, a supercritical focusing optical head can control the polarization state of a focused light field exceeding the diffraction limit. Since light waves are a type of electromagnetic wave, they carry information in multiple physical dimensions besides intensity, including wavelength, polarization, phase, and angular momentum. These physical dimensions are orthogonal, allowing for information multiplexing. Therefore, by controlling the polarization state of the focused light field, different information can be carried in different polarization states under the same intensity of focused light field, thereby further improving the capacity of optical storage and the precision of laser processing.

[0091] Specifically, each of the N annular bands on the entrance pupil surface of the spatial light modulator is divided into a first part and a second part. The boundary between the first and second parts of each of the N annular bands is a straight line passing through the center of the entrance pupil surface, making the two parts equal in size semicircles. The first and second parts of each annular band have different modulation phases, thereby performing 0 / π step phase modulation on the incident light. Specifically, the modulation phase in each of the N sets of modulation parameters includes a first modulation phase and a second modulation phase. The first part corresponds to the first modulation phase, the second part corresponds to the second modulation phase, and the phase difference between the first and second modulation phases is π.

[0092] Because spatial light modulators require a specific polarization state for the incident light—that is, they only respond to linearly polarized light in a specific direction—the polarization state of the focused light field cannot be directly controlled by the light source. The supercritical focusing head also includes a cyclopolarizer to convert the incident light, after phase modulation by the spatial light modulator, into cyclopolarized light. Due to the 0 / π step phase modulation in the spatial light modulator, the focused light field after passing through the cyclopolarizer is actually a purely transversely polarized light field whose polarization orientation coincides with the boundary line of the 0 / π step phase. Through this method, since the direction of the 0 / π step phase boundary line can be arbitrarily set, it is possible to modulate pre-polarized light in a specific direction into linearly polarized light in any direction as needed.

[0093] To achieve the combination of polarization state modulation and supercritical modulation, the supercritical condition preset in step S230 of the method for determining modulation parameters also needs to be supplemented with corresponding content. Specifically, in addition to the content mentioned above, the supercritical condition may also include that the polarization orientation purity of the focused light field generated by the spatial light modulator at the focal point is greater than 90%, and that the polarization orientation is in the same direction as the boundary line.

[0094] As an example, when setting the initial modulation parameters in S210, the initial modulation phase can be set as a direct superposition of the 0 / π step phase and the superoscillating ring phase. That is, the initial modulation phase in each of the N initial modulation parameters includes the first initial modulation phase and the second initial modulation phase. The first part of each of the N rings corresponds to the first initial modulation phase, and the second part of each of the N rings corresponds to the second initial modulation phase. The phase difference between the first initial modulation phase and the second initial modulation phase is π. In S230, the preset supercritical conditions are that the polarization orientation purity of the main lobe is greater than 90%, the full width at half maximum (FWHM) of the main lobe point spread function is less than 0.61λ / NA and greater than or equal to 0.38λ / NA, and the normalized intensity of the maximum sidelobe is less than 0.3.

[0095] By further dividing the ring into two semicircular parts and superimposing a stepped phase with a phase difference of π on each part, phase modulation of the 0 / π stepped phase is achieved. Based on the supercritical focused light field, vector modulation of the focused light field is realized, which can generate a high-purity transversely linearly polarized focused light spot that breaks through the diffraction limit and whose polarization direction is arbitrarily controllable, thereby expanding the dimensions of high-density optical storage and laser processing.

[0096] In other possible implementations, a supercritical focusing optical head can control the number of focal points in a focused light field that exceeds the diffraction limit. A multifocal array generated by a single spatial light modulator can simultaneously perform optical storage or laser processing, achieving parallel storage or processing and thus improving efficiency.

[0097] Specifically, the modulation phase in each of the N sets of modulation parameters also includes a grating shift phase. This grating shift phase causes each of the N ring zones to modulate the phase of the incident light, generating M beams of diffracted light in different directions. The M beams of diffracted light generated by each of the N ring zones... n All diffracted beams can coherently converge at the focal plane to produce the Mth beam. n There are M focal points, such that the focused light field produces M focal points at different positions on the focal plane, where M is a positive integer greater than 1. n It is a positive integer less than or equal to M.

[0098] To achieve the combination of polarization state modulation and supercritical modulation, the supercritical condition preset in step S230 of the method for determining modulation parameters also needs to be updated accordingly. Specifically, each of the M focal points needs to satisfy a preset supercritical condition.

[0099] As an example, when setting the initial modulation parameters in S210, the initial modulation phase can be set as a direct superposition of the grating displacement phase and the superoscillating ring phase. That is, the initial modulation phase in each of the N initial modulation parameters includes the grating displacement phase through the grating displacement function. In S230, the preset supercritical conditions can include M sets of sub-conditions corresponding one-to-one with the M focal points of the focused light field. Each set of sub-conditions can set the main lobe size and side lobe normalization intensity of the corresponding focal point. The sub-conditions of different focal points can be the same or different. Each of the M focal points in the focused light field generated under the adjusted N sets of initial modulation parameters satisfies the corresponding sub-condition.

[0100] Optionally, multifocal modulation of the focused optical field can be applied to a focused optical field without polarization modulation or to a focused optical field modulated by polarization state. When applied to a focused optical field modulated by polarization state, the initial modulation phase can be set as a superposition of the 0 / π step phase, the superoscillating ring phase, and the grating displacement phase; in the supercritical focusing condition, the sub-conditions corresponding to different focal points can also include the polarization orientation of that focal point.

[0101] By superimposing grating displacement phase modulation on each ring zone, the focused spot is moved off-axis, thereby achieving arbitrary control of the spatial position of the focused spot. Furthermore, multiple focal points at different positions exist in the focal plane of the focused light field, which can generate a multi-focal focused spot that breaks through the diffraction limit, thereby improving the efficiency of high-density optical storage and laser processing.

[0102] The above text combined Figure 1 and Figure 2 This application describes the method for generating a supercritical focused optical field and the method for determining modulation parameters. The following section combines... Figure 3 The experimental verification results provided in the figure illustrate the specific effects of the supercritical focused light field provided in the embodiments of this application.

[0103] Figure 3 and Figure 4 This is the experimental result diagram of the fluorescence readout verification experiment. A 100nm fluorescent microsphere was used as the test sample. An unmodulated diffraction-limited confocal imaging system was used as the control group, and the multifocal supercritical focusing light field meeting the supercritical conditions provided in this application's embodiments was used as the experimental group. Scanning imaging was performed on both systems. The incident laser used was an 800nm ​​femtosecond laser, and the focusing lens had a numerical aperture of 0.9. Figure 3 These are fluorescence imaging images of the control group and the experimental group. Figure 3 (a) is the control group. Figure 3(b) represents the experimental group. It can be seen that the two particles marked along the dotted line in the figure cannot be distinguished under the diffraction-limited conditions of the control group, but can be clearly distinguished under the supercritical focusing conditions of the experimental group. Figure 4 This image shows a comparison of the point spread function of isolated fluorescent spots at the same location in fluorescence imaging under control and experimental conditions. Figure 4 (a) is Figure 3 The point diffusion functions of the control and experimental groups corresponding to particles marked ① are shown in the figure. Figure 4 (b) is Figure 3 The point spread functions of the control and experimental groups corresponding to particles marked ② are shown in the figure. It can be seen that the full width at half maximum (FWHM) of the control group peak is 489 nm, close to the Rayleigh criterion of 0.61λ / NA, while the FWHM of the experimental group peak is 320 nm, close to the superoscillation criterion of 0.38λ / NA. These experimental results verify the super-resolution capability of the supercritical focused light field provided in the embodiments of this application.

[0104] Figure 5 and Figure 6 This is an experimental result image of the super-resolution recording effect. Two letters "H" were recorded using dark pixels under a 400nm pixel pitch. An unmodulated diffraction-limited confocal imaging system was used as the control group, and the multifocal supercritical focusing light field satisfying supercritical conditions provided in this application's embodiments was used as the experimental group. Figure 5 To record the effect diagram, among which, Figure 5 (a) shows the results of the control group, where it can be seen that the two letters H are not clearly readable or writable. Figure 5 (b) shows the results recorded by the experimental group, where it can be seen that both letters H can be read and written clearly. Figure 6 The transverse intensity maps recorded for the control and experimental groups show that the experimental group exhibits greater transverse intensity variation between adjacent points compared to the control group, corresponding to stronger brightness resolution and thus more clearly recording the intensity characteristics of the pattern. By using a focused light field that meets supercritical conditions, the spacing between recording points can be reduced from 500 nm (diffraction limit) to 400 nm, corresponding to an increase in optical storage areal density from 5 GB to 7.8 GB, an improvement of more than 50%.

[0105] Figure 7 and Figure 8 This image shows the experimental results of a dot-matrix storage experiment on polymethyl methacrylate (PMMA) polymer material. A femtosecond laser with a center wavelength of 517 nm and a focusing lens with a numerical aperture of 0.85 were used. Dot-matrix writing and reading experiments were conducted on PMMA polymer material using both unmodulated laser and laser modulated according to the method provided in this application to meet supercritical conditions. Figure 7The results of writing and reading with unmodulated laser are shown. (a) is an image of gold nanoparticles, and (b) is a scan of the point spread function of gold nanoparticles. It can be seen that the full width at half maximum (FWHM) of the point spread function is 342 nm, which is close to the Rayleigh criterion of 0.61λ / NA. Figure 8 The images show the writing and reading results of the laser after modulation to meet the supercritical condition. (a) is an image of the gold nanoparticles, and (b) is a scan of the point spread function of the gold nanoparticles. It can be seen that the full width at half maximum (FWHM) of the point spread function is 266 nm, which exceeds the Rayleigh criterion of 0.61λ / NA and is greater than the superoscillation criterion of 0.38λ / NA.

[0106] Figures 9 to 12 This is a graph showing the experimental results of a point-by-point verification experiment on PMMA polymer material. Figure 9 The images show the recordings and transverse intensity maps of the unmodulated laser at a dot pitch of 500*500nm. Figure 10 The images show the recording and transverse intensity diagrams of a modulated laser satisfying supercritical conditions at a dot pitch of 500*500 nm. Different laser intensities were used for the recording points in different rows. It can be seen that the full width at half maximum (FWHM) of each point in multiple recording points is clearly displayed under both laser intensities. These experimental results demonstrate that both modulated and unmodulated lasers can be clearly recorded and read at the diffraction limit of 500*500 nm. However, when the recording pitch is reduced to 400*400 nm, differences will appear in the recording results between modulated and unmodulated lasers. Figure 11 The images show the recordings and transverse intensity maps of the unmodulated laser at a dot pitch of 400*400nm. Figure 12 The images show the recording pattern and transverse intensity map of a modulated laser satisfying supercritical conditions at a dot pitch of 400*400nm. Different rows of recording points use different laser intensities. The experimental results show that when using an unmodulated laser at a dot pitch of 400*400nm, interference between adjacent recording points blurs the recorded pattern. Therefore, reading, writing, and resolving of 400*400nm recording points can only be achieved within a certain energy window. Furthermore, the transverse intensity map shows that the smaller dot pitch prevents the complete display of the full width at half maximum (FWHM) of each recording point. However, when using a modulated laser satisfying supercritical conditions at a dot pitch of 400*400nm, each recording point can be clearly distinguished under any intensity condition, and the transverse intensity map clearly displays the full WHM of each recording point.

[0107] Figures 13 to 15 This is a demonstration image illustrating the effect of applying a multi-focal, multi-polarization focused light field satisfying supercritical conditions to parallel storage, as provided in an embodiment of this application. The experiment achieved multi-focal supercritical focusing by loading a modulation function, with the size of the main lobe of each focal point controlled at 0.38λ / NA. Figure 13As shown, the interaction between multi-polarization, multi-focus and disordered coupled nanoparticles was demonstrated, thereby verifying the multidimensional parallel read / write capability. Figure 14 The diagram illustrates the data recording and reading process. By statistically analyzing the intensity distribution of the read fluorescence pattern, a suitable binarization threshold is selected to obtain the final read fluorescence pattern. This pattern is then compared with the target recorded pattern to obtain the bit error rate of the recorded pattern.

[0108] Figure 15 The experiment shown employs a 2x2 supercritical focal array. The polarization direction of each focal point is set to horizontal, vertical, 45°, and 135°, respectively. Each focal point corresponds to a different position in space, and parallel recording is achieved by controlling the 0 / 1 intensity of each focal point through independent switches. Figure 15 The image shows the parallel recording of four patterns and their corresponding fluorescence readout data. In the experiment, by using a dot pitch of 400 nm, compared with the diffraction-limited dot pitch of 500 nm, the single-channel optical storage areal density was increased from 5 GB to 7.8 GB, and the parallel read / write rate of the four channels was increased by 4 times. Therefore, the two-by-two polarization multiplexing method can increase the total density to 31 GB.

[0109] The above text combined Figure 1 and Figure 15 This application describes the method for generating a supercritical focused optical field and the method for determining modulation parameters. The following section combines... Figure 16 The present application provides an embodiment of the supercritical focusing optical head device.

[0110] Figure 16 A schematic structural block diagram of a supercritical focusing optical head 1600 provided in an embodiment of this application is shown.

[0111] like Figure 16 As shown, the supercritical focusing optical head 1600 includes a light source 1610 and a spatial light modulator 1620.

[0112] Specifically, the light source 1610 is used to generate incident light.

[0113] Specifically, the spatial light modulator 1620 is used to modulate the phase of incident light to generate a focused light field that satisfies supercritical conditions. The entrance pupil surface of the spatial light modulator includes N annular bands, each corresponding to one of N sets of modulation parameters. Each of the N sets of modulation parameters includes a band width and a modulation phase. Each of the N annular bands modulates the phase of the incident light under its corresponding modulation parameters to generate diffracted light. The coherence of the diffracted light generated by the N annular bands ensures that the focused light field satisfies supercritical conditions. N is a positive integer greater than 1, and the N sets of modulation parameters are obtained based on the supercritical conditions. The specific supercritical conditions and the method for determining the N sets of modulation parameters can be found in the descriptions in the preceding method embodiments, and will not be repeated here.

[0114] Optionally, the supercritical focusing optical head 1600 may also include a cyclopolarizer 1630 for converting the focused optical field.

[0115] It should be understood that Figure 16 The spatial light modulator 1620 shown can function as a single spatial light modulator or multiple spatial light modulators. As an example, when the spatial light modulator 1620 is performed by a single spatial light modulator, this modulator provides the modulation phase determined according to supercritical conditions, i.e., the final superposition of all adjusted phases, including the 0 / π step phase, the super-oscillating annular phase, and the grating shift phase. When the spatial light modulator 1620 is performed by multiple spatial light modulators, each modulator can provide its own adjusted modulation phase, such as the 0 / π step phase, the super-oscillating annular phase, or the grating shift phase.

[0116] This application embodiment also provides an optical storage system, which includes at least one such optical storage system. Figure 16 The supercritical focusing optical head shown in the 1600 supercritical focusing optical head.

[0117] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the embodiments of this application.

Claims

1. A method for generating a supercritical focused optical field, characterized in that, The method is applied to a supercritical focusing optical head, the supercritical focusing optical head including a light source and a spatial light modulator, the method comprising: The light source generates incident light; The spatial light modulator modulates the phase of the incident light to generate a focused light field that satisfies the supercritical condition. The entrance pupil of the spatial light modulator includes N annular bands, each corresponding to one of N sets of modulation parameters. Each of the N sets of modulation parameters includes a band width and a modulation phase. Each of the N annular bands modulates the phase of the incident light under the corresponding modulation parameters to generate diffracted light. The coherence of the diffracted light generated by the N annular bands ensures that the focused light field satisfies the supercritical condition. N is a positive integer greater than 1. The N sets of modulation parameters are obtained based on the supercritical condition, which includes that the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, and that the full width at half maximum (FWHM) of the focal spot of the focused light field generated by the spatial light modulator at the focal point satisfies: Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head.

2. The method according to claim 1, characterized in that, The supercritical focusing optical head further includes a cyclopolarization converter, and the spatial light modulator modulates the phase of the incident light to generate a focused optical field that satisfies the supercritical condition, including: The spatial light modulator modulates the phase of the incident light to generate a focused light field. Each of the N rings is divided into a first part and a second part. The boundary between the first part and the second part of each of the N rings is a straight line passing through the center of the entrance pupil. The modulation phase in each of the N sets of modulation parameters includes a first modulation phase and a second modulation phase. The first part corresponds to the first modulation phase, and the second part corresponds to the second modulation phase. The phase difference between the first modulation phase and the second modulation phase is π. The cyclopolarizer converts the focused light field so that the focused light field satisfies the supercritical condition. The supercritical condition also includes that the polarization orientation purity of the focused light field generated by the spatial light modulator at the focal point is greater than 90%, and that the polarization orientation is in the same direction as the boundary line.

3. The method according to claim 1 or 2, characterized in that, The spatial light modulator modulates the phase of the incident light to generate a focused light field that satisfies the supercritical condition, including: The spatial light modulator modulates the phase of the incident light. Each of the N sets of modulation parameters includes a grating shift phase in its modulation phase. This grating shift phase causes each of the N ring bands to modulate the phase of the incident light, generating M beams of diffracted light in different directions. The Mth beam generated by each of the N ring bands... n The diffracted beams coherently converge at the focal plane to produce a focal point, such that the focused light field includes M focal points at different positions on the focal plane, each of the M focal points satisfying the supercritical condition, where M is a positive integer greater than 1. n It is a positive integer less than or equal to M.

4. The method according to any one of claims 1 to 3, characterized in that, The method further includes: Determine N sets of initial modulation parameters that correspond one-to-one with the N ring bands. Each set of initial modulation parameters includes an initial ring band width and an initial modulation phase. Determine the initial intensity distribution, which is the intensity distribution of the focused light field generated by the spatial light modulator under the N sets of initial modulation parameters; Based on the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted so that the intensity distribution of the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the supercritical condition. The values ​​of the N sets of modulation parameters are determined to be the adjusted values ​​of the N sets of initial modulation parameters.

5. A supercritical focusing optical head, characterized in that, include: A light source, used to generate incident light; A spatial light modulator is used to modulate the phase of the incident light to generate a focused light field that satisfies a supercritical condition. The entrance pupil of the spatial light modulator includes N annular bands, each corresponding to one of N sets of modulation parameters. Each of the N sets of modulation parameters includes a band width and a modulation phase. Each of the N annular bands modulates the phase of the incident light under the corresponding modulation parameters to generate diffracted light. The coherence of the diffracted light generated by the N annular bands ensures that the focused light field satisfies the supercritical condition. N is a positive integer greater than 1. The N sets of modulation parameters are obtained based on the supercritical condition, which includes that the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, and that the full width at half maximum (FWHM) of the focal spot of the focused light field generated by the spatial light modulator at the focal point satisfies: Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head.

6. The supercritical focusing optical head according to claim 5, characterized in that, The spatial light modulator is used for: The phase of the incident light is modulated to generate a focused light field, wherein each of the N rings is divided into a first part and a second part, and the boundary between the first part and the second part of each of the N rings is a straight line passing through the center of the entrance pupil surface. The modulation phase in each of the N sets of modulation parameters includes a first modulation phase and a second modulation phase, the first part corresponds to the first modulation phase, the second part corresponds to the second modulation phase, and the phase difference between the first modulation phase and the second modulation phase is π. The supercritical focusing optical head also includes a cyclopolarization converter for: The focused light field is transformed so that it satisfies the supercritical condition. The supercritical condition also includes that the polarization orientation purity of the focused light field generated by the spatial light modulator at the focal point is greater than 90%, and that the polarization orientation is in the same direction as the boundary line.

7. The supercritical focusing optical head according to claim 5 or 6, characterized in that, The spatial light modulator is used for: The phase of the incident light is modulated, wherein the modulation phase in each of the N sets of modulation parameters includes a grating shift phase. The grating shift phase causes each of the N ring zones to modulate the phase of the incident light, generating M beams of diffracted light in different directions. The Mth beam generated by each of the N ring zones... n The diffracted beams coherently converge at the focal plane to produce a focal point, such that the focused light field includes M focal points at different positions on the focal plane, each of the M focal points satisfying the supercritical condition, where M is a positive integer greater than 1. n It is a positive integer less than or equal to M.

8. A method for determining modulation parameters, characterized in that, The method is applied to a supercritical focusing optical head, which includes a light source and a spatial light modulator. The entrance pupil surface of the spatial light modulator includes N annular bands. The spatial light modulator is used to modulate the phase of the incident light to generate a focused light field. The N annular bands correspond one-to-one with N sets of modulation parameters. Each set of modulation parameters includes an annular band width and a modulation phase, where N is a positive integer greater than 1. The method includes: Determine N sets of initial modulation parameters that correspond one-to-one with the N ring bands. Each set of initial modulation parameters includes an initial ring band width and an initial modulation phase. Determine the initial intensity distribution, which is the intensity distribution of the focused light field generated by the spatial light modulator under the N sets of initial modulation parameters; Based on the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted so that the intensity distribution of the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the supercritical condition. The supercritical condition includes that the intensity of the focused light field generated by the spatial light modulator at positions other than the focal point on the optical axis is less than the intensity of the focused light field generated by the spatial light modulator at the focal point, and that the full width at half maximum (FWHM) of the focal spot of the focused light field generated by the spatial light modulator at the focal point satisfies: Where R is the full width at half maximum (FWHM) of the focal spot, λ is the wavelength of the incident light, and NA is the numerical aperture of the supercritical focusing head. The values ​​of the N sets of modulation parameters are determined to be the adjusted values ​​of the N sets of initial modulation parameters.

9. The method according to claim 8, characterized in that, Each of the N ring bands is divided into a first part and a second part. The dividing line between the first part and the second part of each of the N ring bands is a straight line passing through the center of the entrance pupil surface. Determining the N sets of initial modulation parameters corresponding one-to-one with the N ring bands includes: N sets of initial modulation parameters are determined, each corresponding to one of the N ring bands. The initial modulation phase in each set of initial modulation parameters includes a first initial modulation phase and a second initial modulation phase. The first part of each ring band in the N ring bands corresponds to the first initial modulation phase, and the second part of each ring band in the N ring bands corresponds to the second initial modulation phase. The phase difference between the first initial modulation phase and the second initial modulation phase is π. The step of adjusting the N sets of initial modulation parameters according to the initial intensity distribution and supercritical conditions includes: Based on the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted so that the intensity distribution of the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the supercritical condition. The supercritical condition also includes that the polarization orientation purity of the focused light field generated by the spatial light modulator at the focal point is greater than 90%, and that the polarization orientation is in the same direction as the boundary line.

10. The method according to claim 8 or 9, characterized in that, The determination of the N sets of initial modulation parameters corresponding one-to-one with the N ring bands includes: N sets of initial modulation parameters are determined, each corresponding one-to-one with the N annular bands. Each set of initial modulation parameters includes an initial modulation phase that further comprises a grating shift phase. This grating shift phase causes each of the N annular bands to modulate the phase of the incident light, generating M beams of diffracted light in different directions. The Mth beam generated by each of the N annular bands... n The diffracted beams coherently converge at the focal plane to produce a focal point, such that the focused light field includes M focal points at different positions on the focal plane, where M is a positive integer greater than 1. n A positive integer less than or equal to M; The supercritical condition includes M sets of sub-conditions corresponding one-to-one with the M focal points of the focused optical field. Adjusting the N sets of initial modulation parameters based on the initial intensity distribution and the supercritical condition includes: Based on the initial intensity distribution and the supercritical condition, the N sets of initial modulation parameters are adjusted so that each of the M focal points in the focused light field generated by the spatial light modulator under the adjusted N sets of initial modulation parameters satisfies the corresponding sub-condition.

11. The method according to any one of claims 8 to 10, characterized in that, The step of adjusting the N sets of initial modulation parameters according to the initial intensity distribution and supercritical conditions includes: Based on the genetic algorithm and / or particle swarm optimization algorithm, the N sets of initial modulation parameters are adjusted according to the initial intensity distribution and the supercritical condition.

12. An optical storage system, characterized in that, It includes at least one supercritical focusing optical head, said at least one supercritical focusing optical head being used to perform the method as described in any one of claims 1 to 4.

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