Zooming meta-lens group and imaging system

Abstract

The application discloses a zooming super-structured lens set and an imaging system. The zooming super-structured lens set comprises a first super-structured lens and a second super-structured lens which are stacked along the self-axial direction and are separately arranged, at least one of the first super-structured lens and the second super-structured lens rotates around the self-axial line, and the focal length of the zooming super-structured lens set continuously changes with the change of the relative rotation angle of the first super-structured lens and the second super-structured lens. The application changes the focusing phase gradient of the whole lens set by the complementary discrete phase accumulation between the two super-structured lenses which are cascaded and stacked, so that the continuous focal length change is realized.

Description

Technical Field

[0001] This invention specifically relates to a zoom meta-lens assembly and imaging system, belonging to the technical field of meta-lens and imaging detection. Background Technology

[0002] The observation of the internal composition of matter has brought about a completely new understanding beyond the appearance of structure. Electromagnetic imaging beyond the visible light band has further enriched the information about the material world beyond human perception. A typical imaging system includes an irradiation source, the object under test, a detection device, and supporting optical components and optomechanical systems. These components work together to acquire transmitted and reflected electromagnetic images and videos that carry information about the internal structure of matter.

[0003] The terahertz band lies between microwave electronics and infrared photonics. The inherent difficulties in developing functional components for this band have resulted in a relatively low level of technological maturity at present, creating what is known as the terahertz gap. As a strategically important spectral resource, terahertz waves offer higher imaging resolution compared to microwaves and millimeter waves. Furthermore, their photonic power is lower than that of X-rays and infrared rays, providing unique advantages in non-contact imaging, such as no ionizing damage, greater penetration depth, and characteristic fingerprint spectra. Terahertz imaging is primarily used in non-contact human body security checks using active irradiation, non-destructive testing of internal defects in aerospace composite materials, and high affinity and characteristic identification of biomedical samples.

[0004] Current terahertz imaging schemes mostly rely on single-channel detection or one-dimensional linear array detection synthesis imaging. These typically require the target object to participate in displacement scanning. A typical scheme includes point-by-point scanning imaging systems based on terahertz time-domain spectroscopy. These systems utilize broadband terahertz pulses to penetrate the object, perform multiple displacements within the imaging plane, and collect transmitted signals to resolve internal absorption or depth-related information of the object within the plane. The drawback of this type of channel synthesis imaging is the long image frame acquisition time; the imaging resolution is linearly related to the displacement scanning accuracy, and its image acquisition mechanism inevitably limits its application in real-time dynamic imaging. Furthermore, regarding single-channel imaging, there are imaging schemes based on a combination of spatial light modulators and compressed sensing algorithms. These schemes recover image information by illuminating multiple sets of structured light-modulated snapshots and measuring the intensity of single-channel detection, combined with algorithms. Currently, these schemes lack mature large-array partitioned modulation devices and are susceptible to terahertz wave diffraction, making it difficult to obtain high-resolution images. CN116678850A proposes a point-scanning terahertz nondestructive testing system, including a signal acquisition device and a displacement control platform. This system allows for multi-dimensional information detection and analysis of the sample under test through point-by-point scanning. CN218823917U proposes a scanning imager that uses a stepper motor to drive the movement of a dielectric plate on an object, and displays imaging contours, spectra, and other information through image stitching.

[0005] Another technical approach is non-synthetic synchronous imaging based on two-dimensional area array detection. This type of system uses an array detector placed at the imaging focal plane (image plane) to collect the intensity of transmitted signals in space. Combined with timing readout circuitry and image preprocessing algorithms, it can refresh the image in real time or record dynamic video. The imaging resolution of this approach is related to the numerical aperture of the camera lens and the pixel density and scale of the sensor array. This real-time image acquisition mechanism is highly advantageous for observing the dynamic evolution of samples and adjusting observation parameters in real time, making it the most promising terahertz imaging scheme. Currently, mainstream terahertz array imaging sensors have developed prototypes based on all-CMOS (Complementary Metal Oxide Semiconductor) technology and GaN (Gallium nitride) HEMT (High Electron Mobility Transistor)-CMOS heterogeneous integration technology. These prototypes already possess the conditions for high-quality terahertz imaging applications in terms of detection sensitivity, pixel density and scale, imaging frame rate, and detection consistency. For example, the typical sensitivity of a GaN HEMT-CMOS array imaging sensor is below 100 pW / Hz. -1 / 2The pixel pitch reaches half a wavelength scale, the array size reaches 128×128, the imaging frequency can meet customized designs within the range of 0.1~1.2THz, and the imaging frame rate can reach 60FPS (Frames Per Second). CN115951421A proposes a channel-type terahertz active imaging human security inspection system, which scans the object to be tested by radiating terahertz waves. A fixed-focus terahertz camera collects the scattered signals, realizing non-contact detection of human bodies or biological tissues, effectively avoiding radiation damage. CN116879169A proposes a lensless camera imaging device, which solves the interference noise caused by the back-and-forth reflection of terahertz waves between the detector window and the imaging target in traditional lensless coherent imaging systems by irradiating the scattering medium. It can be seen that most current terahertz imaging systems are configured with lensless or fixed-focus lenses, and the accompanying lens groups are mostly based on monochromatic fixed-focus geometric optics design. Because lens materials have low refractive indices in the terahertz band, lens thicknesses typically reach tens of centimeters, and the curvature of the mirror surface varies significantly, inevitably leading to drawbacks such as large size, heavy weight, and high manufacturing costs. For example, CN116224553A proposes an ultra-wide-angle lens group suitable for terahertz focal plane cameras, comprising a meniscus negative lens, two aspherical lenses, a focal plane protection lens, and an aperture stop, etc., using TPX material. The maximum lens thickness at approximately 3.0 THz (wavelength 100 μm) is 35 mm, and the focal length of the lens group is fixed at 12 mm. CN113866931A proposes a lens barrel comprising a reflective parabolic mirror and a lens structure combination, used for collimating and refocusing diverging beams in specific optical path scenarios, but its application scenarios are still relatively limited.

[0006] However, the fixed focal length lens group design limits the ability to observe sample details at variable magnification and is difficult to adapt to application scenarios such as observing samples of different scales. For imaging systems that meet observation requirements in the terahertz band, the zoom metalens group, as the core component determining the system's imaging quality and observation capabilities, plays a significant role in variable magnification observation and high signal-to-noise ratio imaging. Zoom imaging systems require continuously adjustable focal length within a certain range, good image quality during zooming, and different object plane observation apertures due to the fixed image plane position.

[0007] Traditional zoom systems employ lens design based on Gaussian optical calculations to achieve focal length allocation and meet system parameters, broadly categorized into optical compensation and mechanical compensation. Optical compensation can only achieve zoom systems with low magnification ratios and small relative apertures, and the focal length is limited to only a few discrete values, thus imposing many limitations in use. In contrast, zoom systems using mechanical compensation can continuously change the focal length within a certain range. The basic principle is to utilize the coordinated movement of multiple lens groups within the system to alter the combined focal length. Lens groups designed using mechanical compensation typically require a mechanical system to assist in the longitudinal translation of the compensation lens groups. Furthermore, the number of lens groups meeting design requirements is usually difficult to reduce, and they are often aspherical structures. This inevitably leads to disadvantages in manufacturing processes and costs. To manufacture multiple lens groups with various shapes, such as freeform surfaces and aspherical lenses, high-precision machining or even manual processing is required, involving grinding, polishing, and coating processes to meet requirements for processing accuracy and transmission efficiency. Limited by the mechanical compensation focusing mechanism, air gaps need to be reserved between multiple lens groups, leading to high assembly precision requirements. This also necessitates reserving redundant space to compensate for lens displacement during zooming. Furthermore, this type of traditional zoom lens assembly design is only suitable for specific focal lengths; for different wide-angle, telephoto, and other applications, lens replacement is required. In the terahertz band, due to the relatively large and bulky size of the lens groups and limited mechanical drive capabilities, manual spiral zoom lens groups are predominantly used. The optical zoom process typically involves longitudinal displacement between lens elements, causing changes in lens volume. In a relatively compact and fixed terahertz imaging system, this inevitably increases the complexity of the zoom system's structural design and may even encroach on the space of the imaging target, causing mechanical interference. Summary of the Invention

[0008] The main objective of this invention is to provide a zoom meta-lens group and imaging system, thereby overcoming the shortcomings of the prior art.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] A first aspect of the present invention provides a zoom meta-lens group comprising: at least one first meta-lens and at least one second meta-lens stacked and separately disposed along their own axis, wherein at least one of the first meta-lens and the second meta-lens rotates about its own axis, and the focal length of the zoom meta-lens group continuously changes with the relative rotation angle of the first meta-lens and the second meta-lens.

[0011] Furthermore, both the first and second metalenses include multiple phase modulation units with subwavelength scales.

[0012] The phase distribution φ1 of the first meta-lens satisfies:

[0013]

[0014] The phase distribution φ2 of the second meta-lens satisfies:

[0015]

[0016] The focal length f of the zoom meta-lens group is:

[0017]

[0018] in, denoted as the relative rotation angle between the first and second metalenses, in rad; and f0 as the initial focal length of the zoom metalens group. The initial rotation angle is determined by the initial focal length f0, r is the straight-line distance from the center position of the phase modulation unit to the center position of the first meta-lens / second meta-lens, and λ refers to the wavelength of the electromagnetic wave at the operating frequency.

[0019] Furthermore, the phase modulation unit is a dielectric pillar structure with a double-sided cylindrical structure, and the multiple dielectric pillar structures contained in either the first meta-lens or the second meta-lens have the same height but different radial cross-sectional areas.

[0020] Furthermore, both the first metalens and the second metalens include a phase modulation layer, a support substrate layer, and an antireflection layer stacked sequentially along their own axial direction. The phase modulation layer includes a plurality of phase modulation pillars, and the antireflection layer includes a plurality of antireflection pillars. Each phase modulation pillar corresponds to an antireflection pillar in its own axial direction. Each phase modulation pillar, an antireflection pillar, and the support substrate layer located between the phase modulation pillar and the antireflection pillar form the phase modulation unit. The phase modulation layer of the first metalens faces the antireflection layer of the second metalens.

[0021] Understandably, the first meta-lens and the second meta-lens have the same structure. The top layer of both is a phase modulation layer, which is a feature pattern layer containing multiple phase modulation pillars arranged in an array and having phase modulation function. The middle layer, the supporting substrate layer, has patterned structures on both sides. The bottom layer, the anti-reflection layer, is a matching patterned layer composed of multiple anti-reflection pillars arranged in an array, which reduces electromagnetic wave reflection. The supporting substrate layer serves as a material substrate, supporting the front phase modulation layer patterned structure and the back anti-reflection layer patterned structure. The phase modulation layer, the supporting substrate layer, and the anti-reflection layer patterned structure are stacked sequentially to form a monolithic lens.

[0022] Furthermore, the phase modulation layer, the supporting substrate layer, and the antireflection and anti-reflection layer are made of the same material.

[0023] Furthermore, the phase modulation layer, the supporting substrate layer, and the antireflection and anti-reflection layer are integrally formed from the same material. For example, both the first metalens and the second metalens are formed by semiconductor micro-nano processing (deep silicon etching) on ​​high-resistivity silicon wafers.

[0024] Furthermore, the phase modulation unit is a dielectric pillar structure, and the axial height of multiple dielectric pillar structures is the same.

[0025] Furthermore, the multiple phase modulation columns have the same axial height but different side lengths / areas of their radial cross sections.

[0026] Furthermore, the resistivity of the materials of the first metalens and the second metalens is ≥10 kΩ·cm to meet the requirements of low absorption loss and high transmittance.

[0027] Furthermore, the effective optical areas (i.e., optical windows) of the first and second metalenses have the same outline shape and size, thus reducing the requirements for pattern preparation and processing. Of course, the sizes of the optical windows of the two can also be set differently for the purpose of saving raw materials and system integration.

[0028] Furthermore, the first meta-lens and the second meta-lens are coaxial and aligned with the same optical axis.

[0029] Furthermore, both the first meta-lens and the second meta-lens are planar lens structures.

[0030] Furthermore, the thickness of the first metalens and the second metalens can be less than or equal to the wavelength of the electromagnetic wave at the operating frequency (advantage of being thinner and lighter), for example, the thickness of the first metalens and the second metalens manufactured for 340GHz (wavelength 880 micrometers) is 800 micrometers.

[0031] In a more specific implementation, the zoom meta-lens group further includes an optomechanical system, which is connected to the first meta-lens and / or the second meta-lens and is used to drive the first meta-lens and / or the second meta-lens to rotate about their own axis, so that the first meta-lens and the second meta-lens rotate relative to each other about their own axis or the same optical axis.

[0032] Furthermore, the optomechanical system includes: a drive mechanism, a drive gear, and at least one driven gear. The drive mechanism is driven by the drive gear and the driven gear. At least one of the first meta-lens and the second meta-lens is fixed on the driven gear and rotates together with the driven gear.

[0033] A second aspect of the present invention provides an imaging system comprising a signal emission source, a first zoom lens group, a second zoom lens group, and an imaging detector arranged sequentially along a selected direction. The first zoom lens group is used to converge the diverging light beam radiated by the signal source to the imaging target, and the second zoom lens group is used to converge the transmitted / reflected light beam of the imaging target to the imaging detector. Both the first zoom lens group and the second zoom lens group are zoom meta-lens groups.

[0034] Furthermore, the zoom lens group further includes a displacement bracket, which is disposed between the first zoom lens group and the second zoom lens group. The displacement bracket is used to support the imaging target and adjust the object distance to present a clear image. The imaging target can move on the displacement bracket along the selected direction.

[0035] Compared with the prior art, the advantages of the present invention include:

[0036] The zoom lens assembly provided in this embodiment of the invention uses a stacked array of two or more planar subwavelength phase modulation microstructures to achieve focal length adjustment of transmitted electromagnetic waves. This eliminates the need for the aspherical or even free-form surface multi-stacked lens combination in traditional zoom lens assemblies. This improvement simplifies the number of lens assemblies and the manufacturing process, and avoids the series of cumbersome processes such as machining, grinding, polishing, and coating of traditional lenses.

[0037] The focusing function of the zoom super-structure lens group provided in this embodiment of the invention is to change the overall focusing phase gradient of the lens group by complementary phase accumulation between two stacked lenses, thereby achieving continuous focal length change. The focusing process is only the in-plane rotation of a single lens, without constituting axial displacement of the lens or even volume change of the lens group, which brings the super-structure zoom lens group to the advantages in integration and zoom form.

[0038] The zoom meta-lens assembly provided by this invention achieves continuous coverage of the entire focal length range, breaking through the limitation of the limited focusing range of traditional zoom lens assemblies due to the limited physical scaling. Combined with an image sensor, it can meet various application scenarios such as wide-angle, telephoto, and microscopic magnification. At the same time, combined with the optomechanical system integration of DC-driven brushless motor, it realizes high-precision focal length control and extensive electronic system expansion capabilities, overcoming the shortcomings of traditional zoom lens assemblies that usually require manual knob adjustment.

[0039] The present invention provides a zoom meta-lens group applied to a microscopic imaging system in the terahertz band, which can realize perspective imaging of sample materials and observation of internal details. The microscopic magnification imaging based on the focusing function of the lens group is beneficial for perspective observation scenarios with weak signal-to-noise ratio. Combined with the electronic system, it can achieve active adaptation and rapid response capability to observation needs. It overcomes the shortcomings of the current stage in the terahertz band, such as the lack of mature zoom lenses, which limits the application of scalable imaging of detector arrays, slow imaging, and inflexible control caused by the large size of the lens group. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the structure and light propagation path of an imaging system provided in a typical embodiment of the present invention;

[0041] Figure 2a , Figure 2b This is a schematic diagram of a zoom meta-lens group provided in a typical embodiment of the present invention;

[0042] Figure 3 This is a comparison between the discrete focusing phase radial distribution and the standard continuous focusing phase of a zoom meta-lens group provided in a typical embodiment of the present invention;

[0043] Figure 4a , Figure 4b This invention provides a typical embodiment of a zoom meta-lens group whose focal length and numerical aperture vary with relative rotation angle. Evolutionary relationships;

[0044] Figure 5 This invention provides a zoom meta-lens group in a typical embodiment of three typical relative rotation angles. Focusing phase characteristics and lens group parameters;

[0045] Figure 6a , Figure 6b This is a schematic diagram of the optical-mechanical system of a zoom meta-lens group provided in a typical embodiment of the present invention;

[0046] Figure 7 This is a parameter comparison between a traditional zoom lens group and a zoom meta-lens group provided in a typical embodiment of the present invention;

[0047] Figure 8 This is a scene demonstration diagram of a terahertz imaging system based on a zoom meta-lens group provided in a typical embodiment of the present invention;

[0048] Figure 9 This is a schematic diagram of the working principle and data flow of an imaging system based on an electronically controlled zoom meta-lens group, provided in a typical embodiment of the present invention. Detailed Implementation

[0049] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate the technical solution, its implementation process, and principles in conjunction with the accompanying drawings and specific embodiments. Unless otherwise specified, the optical components, electronic systems, and motors used in the embodiments of this invention are all known to those skilled in the art and can be obtained through commercial purchase or processing using known techniques in the field.

[0050] This invention proposes a planar lens design based on metasurface design and a stacked zoom metalens assembly, along with an imaging scheme for an integrated radiation source and detection camera with active focusing based on this zoom metalens assembly. The metalens assembly comprises subwavelength-scale phase modulation units arranged in a specific size and spatial layout, featuring subwavelength-scale planarity, lightweight construction, and ease of integration. The phase distribution of the array surface allows for flexible and effective control of the wavefront of transmitted electromagnetic waves. This invention achieves continuous focal length variation by altering the overall focusing phase gradient of the lens assembly through complementary discrete phase accumulation between two cascaded metalenses.

[0051] In summary, the meta-lens design of the zoom meta-lens group in the embodiments of the present invention, due to its planar structural features, allows its subwavelength phase modulation unit to complete the pattern transfer using only contact ultraviolet lithography exposure in micro-nano fabrication processes, which has the advantage of one-step forming. The processing difficulty and steps are greatly simplified compared to traditional lenses.

[0052] The planar lenses with subwavelength thickness also bring the natural advantage of compact integration. The stacked arrangement of two lenses with subwavelength thicknesses maximizes the compression of vertical space. In addition, in this embodiment of the invention, the zoom lens group is designed to operate only by the in-plane rotation of a single lens, without involving axial precession displacement, and the operating volume is fixed, which is beneficial for the integration of the imaging system.

[0053] Functionally, the zoom range almost completely and continuously covers the entire focal length, breaking through the limitations of traditional zoom lenses. Furthermore, leveraging its lightweight and planar design, it employs an integrated high-precision motor to control lens rotation, making a compact and high-precision electrically controlled terahertz zoom system possible. From an imaging system perspective, this invention's terahertz imaging system based on an electrically controlled zoom meta-lens not only overcomes the limitation of traditional scanning aperture synthesis imaging systems in real-time dynamic imaging observation scenarios, but also enhances the adaptability of array-based detector cameras in fine observation scenarios such as real-time variable magnification and low signal-to-noise ratio perspective observation scenarios with adjustable field of view.

[0054] For a more specific implementation plan, please refer to Figure 1 , Figure 1 This is a schematic diagram of the composition and light propagation path of a zoom metasurface lens imaging system provided by an embodiment of the present invention. A zoom metasurface lens imaging system includes: a terahertz signal emitter, a first zoom lens group supporting the signal emitter, an imaging target and a three-axis electric control displacement bracket, an imaging camera (i.e., a type of the aforementioned imaging detector), and a second zoom lens group supporting the imaging camera, which are five main parts. In terms of the light propagation path, the actively irradiated terahertz beam first radiates from the horn antenna of the terahertz signal emitter into free space, and its beam characteristic is a Gaussian divergent beam; after the beam propagates to the first zoom lens group at the emission end, it is converged to a certain extent. The converging ability of the first zoom lens group at the divergent end can be flexibly adjusted according to the divergence angle of the outgoing beam and the distance of the imaging target, forming a relatively converged beam incident on the imaging target. The actively focused beam is incident on the imaging target to overcome the actual use bottlenecks such as weak terahertz radiation power and low signal-to-noise ratio of transmission imaging at the present stage. After the incident terahertz wave penetrates the imaging target, it will carry characteristics related to the depth of propagation direction of the imaging target, absorption inside the imaging target, and interaction inside the imaging target in terms of spatial intensity characteristics. After the terahertz beam passes through the set focal length at the emission end, it further reaches the second zoom lens group on the imaging camera side, and is converged to the imaging focal plane by the second zoom lens group that works in coordination with the sensor of the imaging camera and is received by the array pixels of the camera. At this time, the imaging camera reads out the signal image, which reflects the spatial intensity characteristics of the terahertz beam after penetrating the object, that is, the perspective image of the imaging target.

[0055] It should be noted that when the imaging camera plane is placed in front of the focus of the second zoom lens group, the image formed is an inverted image, and when it is placed behind the focus, it is a positive image. When the zoom metasurface lens imaging system operates, the spatial positions of the terahertz signal emitter, the first zoom lens group supporting the terahertz signal emitter, the imaging camera, and the second zoom lens group supporting the imaging camera are all fixed. The imaging target is set on the three-axis electric control displacement bracket, and the spatial position of the imaging target can be electrically adjusted through the three-axis electric control displacement bracket to observe the transmission image characteristics at the focal length (the imaging focal length affects imaging parameters such as imaging magnification / depth of field, etc.).

[0056] In this imaging system, the terahertz illumination frequency is fixed at a single frequency point (the frequency can be customized according to imaging requirements), the typical frequency is 340 GHz, the wavelength is 880 μm, and the typical value of the radiation power of the terahertz signal emitter is 10 mW; Figure 1 The parameters in is the collimation focal length that matches the divergence characteristics of the terahertz signal emitter, is the focal length of the electrically adjustable terahertz signal emitter, where The physical diameter of the lens optical window is D, which is the lens rotation angle related to focal length adjustment. The imaging target can be a medium-sized bulk material with a thickness distribution, or a non-homogeneous thin film sample with a characteristic thickness. The imaging target should not be a sample with total internal reflection (e.g., metal) or total absorption (e.g., liquid). After transmitting the image through the target, its internal spatial information Obj(x,y,z) is carried by the transmitted wave in the form of spatial light intensity. The focal length after passing through the first zoom lens group is... The second zoom lens group converges light intensity at the focal plane of the imaging camera, where the focal length parameter... The mounting distance of the imaging camera is fixed. The imaging camera with a pixel array of M×N reads the transmission intensity image lmag(m,n,l) of the imaging target, where (m,n) are the pixel coordinates of the imaging camera, and l represents the brightness value of the corresponding pixel and the brightness of the corresponding transmission image.

[0057] During the imaging process, the object distance of the first zoom lens group is adjusted collaboratively. Object distance of the second zoom lens group By measuring the relative displacement (x, y, z) of the imaging target, transmission images can be acquired at different zoom levels and spatial locations. It's even possible to record the observation process at varying magnifications or dynamic video of the imaging target evolving over time. It should be noted that the x and y axis displacements determine the object's position on the observation plane, while the z-axis displacement needs to be determined by the imaging object distance. This is combined to achieve clear imaging.

[0058] The following section will describe the technical solutions and working principles of each core component of the zoom meta-lens imaging system proposed in this invention.

[0059] The first and second zoom lens groups used in this invention have the same structure; both are zoom meta-lens groups. Please refer to Figure 2. A zoom meta-lens group includes: a first meta-lens and a second meta-lens separately arranged. The first and second meta-lens are stacked along their own axes. The first and second meta-lens have different but rotationally complementary phase distribution characteristics (here, complementarity means that the first and second meta-lens must be used as a whole to have zoom function; complementarity here does not refer to structural complementarity, but functional complementarity, which can be compared to the lens group in a traditional optical camera lens). At least one of the first and second meta-lens rotates around its own axis. The focal length of the zoom meta-lens group changes continuously with the change in the relative rotation angle of the first and second meta-lens.

[0060] Specifically, the first metalens and the second metalens have the same lens structure, but they differ mainly in their phase distribution. In some parts below, the first metalens and the second metalens will be referred to as lenses to illustrate their overall structure. Please refer to Figure 2 again. The top of the lens is a phase modulation structure layer that constitutes the focusing phase, the middle is a support substrate layer that provides mechanical support and assembly, and the back is an anti-reflection layer. The phase modulation layer of the first metalens faces the anti-reflection layer of the second metalens. The lens includes multiple phase modulation units with subwavelength scales.

[0061] Specifically, the phase modulation unit is a dielectric pillar structure with a double-sided cylindrical shape. The phase modulation layer includes multiple phase modulation pillars, and the anti-reflection layer includes multiple anti-reflection pillars. Each phase modulation pillar corresponds to an anti-reflection pillar along its own axial direction. Each phase modulation pillar, an anti-reflection pillar, and a supporting substrate layer located between the phase modulation pillars and the anti-reflection pillars form the phase modulation unit. Specifically, the phase modulation unit is a dielectric pillar structure, with multiple dielectric pillars having the same axial height, and multiple phase modulation pillars having the same axial height but different radial cross-sectional side lengths / areas.

[0062] It should be noted that the multiple phase modulation pillars and multiple anti-reflection and anti-reflection pillars are arranged at equal intervals, specifically in a two-dimensional square dot matrix arrangement, and the center-to-center distance between two adjacent pillars is the unit period of the array.

[0063] Understandably, both the first and second metalenses are planar lens structures with an etched pattern array. This invention alters the propagation phase of electromagnetic waves through the phase modulation unit by changing its equivalent refractive index. By controlling the fill rate of the dielectric pillar structure relative to the area of ​​the unetched unit support substrate, the equivalent propagation refractive index is changed, thus causing a change in the transmission phase. This allows the phase modulation unit used in the lens to achieve a quasi-continuous phase modulation capability of 0–360° through size adjustment.

[0064] Specifically, the lens is formed by etching a double-sided polished 4-inch high-resistivity silicon wafer with a resistivity ≥10 kOhm·cm. In an implementation case designed for a 340 GHz terahertz imaging system, the lens thickness is approximately 800 micrometers, the optical window diameter formed by an array of dielectric pillar structures arranged in a two-dimensional square dot matrix can reach approximately 70 mm, the number of phase modulation units is as high as 250×250, and the working focal length of a typical lens group is approximately 100 mm.

[0065] Specifically, the antireflective layer on the back of the lens can maintain the high transmittance of the lens structure throughout the entire phase modulation range. After overall optimization, the electromagnetic transmittance of the lens in the phase modulation range is as low as 84%. Most of the transmission loss is contributed by the dielectric loss propagating inside the three-layer stacked phase modulation unit. This means that the meta-lens has low reflection loss and good energy focusing efficiency.

[0066] Specifically, the first metalens and the second metalens are stacked along their own axis, with the phase modulation layer of the first metalens facing the antireflection and anti-reflection layer of the second metalens. More specifically, the first metalens and the second metalens are coaxial and have the same optical axis. More specifically, the effective optical regions of the first metalens and the second metalens have the same outline shape and size. That is to say, it can be understood that the first metalens and the second metalens are identical in structure except for the phase distribution of the phase modulation layer.

[0067] Specifically, the multiple phase modulation units contained in the phase modulation layers of the first and second metalenses are arranged in a specific size and spatial layout so that the phase distribution φ1 of the first metalens satisfies:

[0068]

[0069] The phase distribution φ2 of the second meta-lens satisfies:

[0070]

[0071] Focal length of zoom super lens group for:

[0072]

[0073] in, denoted as the relative rotation angle between the first and second metalenses, in rad; and f0 as the initial focal length of the zoom metalens group. The initial lens rotation angle is determined by the initial focal length f0, r is the straight-line distance from the center position of the phase modulation unit to the center position of the first metalens / second metalens, which is equivalent to the position radius of the dielectric pillar structure on the lens, λ is the wavelength of the electromagnetic wave at the operating frequency, and φ represents the phase distribution. The focused phase has rotational invariance about the optical axis of the lens, that is, it has the same phase gradient along the radial direction, which can be simplified to a one-dimensional problem along the radial direction. It can be seen that... With relative rotation angle It is an inverse relationship, and the theoretical zoom range covers [±∞, ±f0].

[0074] The zoom meta-lens group provided by this invention satisfies the rotational invariance of the cumulative phase about the optical axis. The radial phase profile and phase gradient curve of the discretely quantized approximate focusing phase and the focusing compensation phase calculated by ideal geometric optics for the zoom meta-lens group provided by this invention are shown below. Figure 3 As shown,

[0075] Discrete focusing phase of zoom super-lens group for:

[0076]

[0077] The ideal focusing phase φ(r) of the zoom meta-lens group is:

[0078]

[0079] Depend on Figure 3 It can be seen that the discrete focusing phase proposed in this invention can still maintain consistency with the desired ideal focusing phase during the lens rotation process. This means that the phase approximation process in this invention will not cause any deviation in the focusing effect. The quantization error caused by the discrete phase processing is almost negligible. The focusing effect of the lens in this invention is comparable to that of traditional monolithic metalenses or even traditional focusing lenses.

[0080] The zoom super-lens group provided by this invention varies with the relative rotation angle Evolutionary relationships such as Figure 4a , Figure 4b As shown, corresponding to positive or negative relative rotation angles, the zoom meta-lens group provided by this invention can achieve divergence or focusing capabilities, with a focal length... With relative rotation angle The numerical aperture (NA) of the zoom superlens group exhibits a reciprocal relationship with the relative rotation angle. (Numerical aperture NA is a parameter characterizing a lens, reflecting its ability to converge light; numerical aperture (NΔ) is a dimensionless number used to measure the angular range of light that an optical system can collect.) Furthermore, the diffraction limit parameter reflects, to some extent, the half-width at half-maximum (HWHM) information of the emitted light spot, affecting the collimation of the emitted light spot and the focal length of the lens group. At that time, the size of the light spot formed by the zoom super lens group is comparable to the aperture of the lens's optical window.

[0081] In a typical implementation example, the focusing phase characteristics and lens group parameters of the zoom meta-lens group provided by this invention at three typical relative rotation angles are as follows: Figure 5 As shown, Figure 5The diagram shows the phase distribution on the first superlens (the first superlens as a fixed lens - Len-1) and the second superlens (the second superlens as a rotating lens - Len-2) of the zoom superlens group under three typical relative rotation angles, as well as the accumulated different focused phase distributions. It can be seen that the focused phase at different rotation angles exhibits a significant phase gradient change. The corresponding lens group data, such as the relative rotation angle, are shown below. By relative rotation angle The resulting focal length Numerical aperture (NA), diffraction limit (DL).

[0082] In a more typical implementation scheme, please refer to Figure 6a , Figure 6b The zoom meta-lens group in this invention further includes an optomechanical system, which is connected to the first meta-lens and / or the second meta-lens and is used to drive the first meta-lens and / or the second meta-lens to rotate around their own axis, so that the first meta-lens and the second meta-lens rotate relative to each other around their own axis.

[0083] Specifically, the optomechanical system includes: a drive mechanism, a drive gear (also known as an active gear), and at least one driven gear. The drive mechanism is engaged with the driven gear via the drive gear. At least one of the first metalens and the second metalens is fixed to the driven gear and rotates with the driven gear around it. Figure 6a , Figure 6b The diagram shows a case where the first meta-lens is fixed, and the second meta-lens is mounted on the driven gear and can rotate together with the driven gear.

[0084] Specifically, the drive mechanism can be an electric brushless DC motor. This miniaturized electric brushless DC motor integrates a microcontroller unit (MCU) and drive control circuitry, enabling real-time, high-speed communication and instruction execution with a host computer. It also boasts high control precision and low static power consumption. Of course, this electric brushless DC motor is commercially available. Specifically, the driven gear carrying the second meta-lens meshes with the drive gear. The two gears have the same module, and the difference in the number of teeth determines the transmission ratio.

[0085] Specifically, the optomechanical system also includes an optomechanical packaging structure (also known as an optomechanical packaging shell). The first meta-lens is mounted on one optomechanical packaging structure, while the drive mechanism, drive gear, driven gear, and second meta-lens are mounted on another optomechanical packaging structure. The two separate optomechanical packaging structures are fastened together to achieve the packaging and assembly of the first and second meta-lenses. The drive gear and driven gear can rotate freely. More specifically, the drive gear, driven gear, and optomechanical packaging structure are connected and supported by bearing guides to reduce friction during operation and enhance stability. The second meta-lens is mounted on the driven gear, and the hollowed-out area in the middle of the driven gear serves as a window for lens mounting and beam transmission, avoiding interference and obstruction of transmitted light by mechanical devices. Due to the transmission ratio between the two gears, the relative rotation angle of the first and second meta-lenses can be controlled by an electrically driven brushless DC motor.

[0086] More specifically, the optomechanical packaging structure has multiple sets of locating pin holes arranged in a ring to ensure assembly accuracy. More specifically, the optomechanical packaging structure is equipped with image sensor locating holes integrated with the image sensor and signal source, as well as complete assembly holes to meet various integrated assembly schemes such as horizontal, vertical, and flat mounting. In addition, the optomechanical packaging structure also has reserved routing channels and interfaces for data communication and power supply, as well as observation holes for the built-in motor and gear meshing adjustment holes. A typical optomechanical packaging structure has a size transmission ratio of 1:2, and the overall thickness of the optomechanical packaging structure can be compressed to about 25mm. A parameter comparison between a traditional zoom lens group and a zoom meta-lens group provided in this embodiment is as follows: Figure 7 As shown.

[0087] In a more specific implementation scheme, in the zoom imaging system, the actively irradiated terahertz beam undergoes wavefront reconstruction of the forward directional beam directly radiated by the horn antenna through a first zoom lens group on one side of the terahertz signal transmitter. This satisfies three functions under different application scenarios: beam divergence angle adjustment, beam collimation, and beam focusing, thus meeting the active illumination requirements under different imaging fields of view. For extreme scenarios such as relatively limited terahertz illumination power and low signal-to-noise ratio due to propagation loss inside thick objects, a focused beam spot is used as a typical scenario for active illumination in the description. Figure 8 The illustration shows a scene demonstration of a terahertz imaging system based on a zoom metalens group provided by an embodiment of the present invention. The active irradiation range of the terahertz signal emission source defines the imaging visible area. Within the visible area, the magnification is changed by zooming the focal length on the imaging camera side. The required imaging focal length can be located by controlling the single rotation of the lens of the metalens group through an electrical signal.

[0088] Specifically, for imaging needs in different scenarios, the zoom transmission imaging mode proposed in this invention can be classified into the following three main observation modes:

[0089] a. Global perspective image under general illumination: The terahertz signal emission source illuminates the entire target with divergent or collimated focal length, and the imaging camera switches to wide-angle receiving focal length. The object distance is adjusted to make the image clear and receive the transmitted signal, so as to directly observe the whole picture of the imaging target, which is conducive to finding the region of interest for further detailed observation.

[0090] b. Focused microscopic selective observation: Focused illumination enables observation of local images of the target under high transmission power density conditions. By adjusting the object distance of the second zoom lens group on the imaging camera side and the z-axis distance of the object, clear observation of the transmitted image at different magnifications can be achieved. In conjunction with the displacement of the XY-axis electrically controlled displacement support, selective observation of specific areas can be achieved.

[0091] c. Coordinated focal plane translation for observing different target depths: The focal length of the first zoom lens group on the side of the terahertz signal transmitter and the focal length of the second zoom lens group on the side of the imaging camera are adjusted in coordination, with one increasing and the other decreasing while keeping the total focal length fixed. This enables the longitudinal movement of the beam focus within the imaging area, and the use of focal plane transformation to achieve clear observation of different depth sections within the imaging target.

[0092] The working principle and data flow of a zoom meta-lens imaging system provided in this embodiment of the invention are as follows: Figure 9As shown, the focal length, numerical aperture, focal spot size, and spatial coordinates of the imaging target of the first / second zoom lens group can be pre-mapped with multiple sets of motor motion modes (such as absolute / relative displacement, incremental displacement, etc.). These parameters, including the instruction library for image acquisition by the imaging camera (such as snapshot, video, image processing, etc.), are pre-encapsulated as low-level call functions in local storage and the host computer program. When an imaging command that meets the user's observation requirements is issued, the function is directly called to calculate and execute the parameters for the coordinated motion of multiple sets of motors. After the motion is executed and verified, image frame acquisition, transmission, processing, and display begin. A data frame feedback loop is formed between the motor motion and camera acquisition for image acquisition confirmation and coordinate information binding. The entire imaging system is powered by 12V DC, and a single power adapter can meet the power supply needs of multiple discrete devices in the system. For data communication, a master-slave serial bus is used to achieve half-duplex communication. Serial communication is widely used, has good device compatibility, and the communication rate meets the requirements of high-speed motion control and high frame rate image transmission. By connecting multiple electrically controlled displacement devices to a single bus, coordinated motion deployment among multiple devices is achieved. For continuously streaming camera image frames, a dedicated data port is provided to avoid data latency and packet loss issues, minimizing wiring overhead. The transmitted image data can be optimized locally on the host computer for secondary image processing and measurement, or real-time image acquisition and storage can be performed via a local data stream disk service configured on the host computer.

[0093] The zoom lens assembly provided in this embodiment of the invention uses two stacked microstructure arrays with planar subwavelength phase modulation to achieve focal length adjustment of transmitted electromagnetic waves. It abandons the multi-stacked lens combination of aspherical or even free-form surfaces in traditional zoom lens assemblies. This improvement simplifies the number of lens assemblies and manufacturing process, and avoids a series of cumbersome processes such as machining, grinding, polishing, and coating of traditional lenses.

[0094] The lens in the zoom metalens assembly provided in this invention is made from silicon wafers with a high insulation coefficient. Silicon wafers exhibit minimal absorption loss in the terahertz band, and the semiconductor processing technology for silicon-based wafers is extremely mature. Double-sided structure fabrication can be achieved using only two processes: contact ultraviolet lithography and reactive ion etching, enabling phase modulation and anti-reflection / reverse optical emission. Reactive ion etching, as a highly anisotropic and selective dry etching technique, significantly improves microstructure consistency and overall lens yield. The simplified processing steps also help control lens manufacturing costs. Furthermore, the double-sided etching manufacturing technology integrating anti-reflection / reverse optical emission structures avoids the low-refractive-index material layer configuration commonly used in terahertz band lens anti-reflection, thus achieving the excellent focusing efficiency of the metalens.

[0095] The zoom meta-lens group provided in this embodiment of the invention is a double-layer all-dielectric thin film. The volume of a single meta-lens is extremely compressed in the longitudinal space of light propagation compared to a traditional curved lens, while the lens diameter is comparable to that of a traditional lens. This allows the longitudinal volume of the optomechanical package to be extremely flat, and the mechanical structure of the optomechanical system can also be greatly simplified.

[0096] Furthermore, unlike traditional zoom lens groups that adjust the propagation path length of transmitted waves by changing the air gap between lenses, the focusing function of the zoom meta-lens group provided in this invention is achieved by accumulating the complementary phase between two stacked lenses, thereby changing the overall focusing phase gradient of the lens group and realizing continuous focal length changes. The focusing process involves only the in-plane rotation of a single lens element and does not constitute a change in the volume of the lens group, resulting in advantages for the meta-zoom lens group in terms of integration and zoom form.

[0097] The zoom meta-lens assembly provided by this invention achieves continuous coverage of the entire focal length range, breaking through the limitation of the limited focusing range of traditional zoom lens assemblies due to the limited physical scaling. Combined with an image sensor, it can meet various application scenarios such as wide-angle, telephoto, and microscopic magnification. At the same time, combined with the optomechanical system integration of DC-driven brushless motor, it realizes high-precision focal length control and extensive electronic system expansion capabilities, overcoming the shortcomings of traditional zoom lens assemblies that usually require manual knob adjustment.

[0098] The present invention provides a zoom meta-lens group applied to a microscopic imaging system in the terahertz band, which can realize perspective imaging of sample materials and observation of internal details. The microscopic magnification imaging based on the focusing function of the lens group is beneficial for perspective observation scenarios with weak signal-to-noise ratio. Combined with the electronic system, it can achieve active adaptation and rapid response capability to observation needs. It overcomes the shortcomings of the current stage in the terahertz band, such as the lack of mature zoom lenses, which limits the application of scalable imaging of detector arrays, slow imaging, and inflexible control caused by the large size of the lens group.

[0099] The present invention provides a zoom meta-lens group based on a dual-lens design with focusing phase discretization and complementary decomposition. The meta-lenses included in the zoom meta-lens group are all composed of a planar microstructure array at the subwavelength scale. The manufacturing and cost advantages of the lenses are far superior to those of traditional aspherical lens groups. At the same time, comparative evaluation has found that its focusing ability (including parameters such as focal length adjustment, numerical aperture, and focal spot size) is comparable to that of traditional aspherical lenses based on geometric optics. In particular, it further achieves continuous coverage of the entire focal length range in the focusing range.

[0100] The present invention provides a zoom meta-lens group, which is a two-piece stacked meta-lens group designed to be continuously adjustable across the entire focal length by rotating a single lens. The focusing process involves only the relative rotation of a single lens, without causing displacement or volume change of the lens group, which is conducive to ultra-compact integration. An electronically controlled zoom optomechanical system is customized for the two stacked lenses, which has fast-response electronically controlled focusing capability and the convenience of electronic integration.

[0101] Based on the meta-lens group of this invention, an active focusing illumination microscopic imaging system suitable for non-natural light is proposed. The system supports imaging observation with continuous adjustment at different magnifications. The active irradiation of the focused beam and the microscopic magnification imaging system design based on the zoom lens group are suitable for internal perspective observation of samples in scenarios with weak illumination light power and weak transmission signal-to-noise ratio, thus improving the overall dynamic range of the perspective imaging system. The all-electronic control and readout system design has the configuration capability to actively adapt to the user's imaging needs, achieving agile observation response and fast dynamic imaging frame rate at varying magnifications.

[0102] The zoom lens group designed in this invention achieves continuous zoom function based on in-plane misalignment rotation between two cascaded phase-anisotropic metaarrays. It is configured as an all-dielectric transmission type, with a compact structure and simple manufacturing. A customized optomechanical system is designed to realize electric focusing.

[0103] In summary, these zoom metalenses based on reconfigurable components typically require external signals to independently control the characteristics of the array units, meaning their design and manufacturing costs are relatively high. Furthermore, the fabricable array size and consistency are more limited compared to the all-dielectric passive array scheme of this invention, resulting in a limited available lens aperture, which in turn restricts its focusing capability and efficiency. Generally, the adjustable focal length of a single-layer reconfigurable zoom metalens is extremely limited; the zoom function is usually just a switching between two discrete states, and active control components also introduce additional losses.

[0104] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A zoom meta-lens group for microscopic imaging in the terahertz band, characterized in that, include: At least one first meta-lens and at least one second meta-lens are stacked and separately arranged along their own axis. Both the first meta-lens and the second meta-lens are planar lens structures. At least one of the first meta-lens and the second meta-lens rotates about its own axis. The focal length of the zoom meta-lens group changes continuously with the change of the relative rotation angle of the first meta-lens and the second meta-lens. Both the first metalens and the second metalens include multiple phase modulation units with subwavelength scales. Phase distribution of the first meta-lens satisfy: ； Phase distribution of the second meta-lens satisfy: ； Focal length of zoom super lens group for: ； in, The relative rotation angle between the first and second metalenses is expressed in rad. This is the initial focal length of the zoom meta-lens group. It is determined by the initial focal length The determined initial rotation angle, It is the straight-line distance from the center position of the phase modulation unit to the center position of the first metalens / second metalens. It is the wavelength of the electromagnetic wave at the operating frequency.

2. The zoom super-lens group according to claim 1, characterized in that: Both the first metalens and the second metalens include a phase modulation layer, a support substrate layer, and an anti-reflection layer stacked sequentially along their own axial direction. The phase modulation layer includes a plurality of phase modulation pillars, and the anti-reflection layer includes a plurality of anti-reflection pillars. Each phase modulation pillar corresponds to an anti-reflection pillar in its own axial direction. Each phase modulation pillar, an anti-reflection pillar, and the support substrate layer located between the phase modulation pillar and the anti-reflection pillar form the phase modulation unit. The phase modulation layer of the first metalens faces the anti-reflection layer of the second metalens.

3. The zoom super-lens group according to claim 2, characterized in that: The phase modulation layer, the supporting substrate layer, and the antireflection and anti-reflection layer are made of the same material.

4. The zoom super-lens group according to claim 3, characterized in that: The phase modulation layer, the supporting substrate layer, and the antireflection and anti-reflection layer are integrally formed from the same material.

5. The zoom super-lens group according to claim 3 or 4, characterized in that: The phase modulation unit is a dielectric pillar structure, and multiple dielectric pillar structures have the same axial height.

6. The zoom super-lens group according to claim 5, characterized in that: The multiple phase modulation columns have the same axial height but different side lengths / areas of their radial cross sections.

7. The zoom super-lens group according to claim 2, characterized in that: The resistivity of the materials of the first meta-lens and the second meta-lens is ≥10 kOhm·cm.

8. The zoom super-lens group according to claim 1, characterized in that: The effective optical regions of the first metalens and the second metalens have the same outline shape and size.

9. The zoom super-lens group according to claim 8, characterized in that: The first meta-lens and the second meta-lens are coaxial and have the same optical axis.

10. The zoom meta-lens group according to claim 1, characterized in that, Also includes: An optomechanical system is connected to the first metalens and / or the second metalens via a transmission, and is used to drive the first metalens and / or the second metalens to rotate about their own axis, so that the first metalens and the second metalens rotate relative to each other about the same optical axis.

11. The zoom super-lens group according to claim 10, characterized in that: The optomechanical system includes: a drive mechanism, a drive gear, and at least one driven gear. The drive mechanism is driven by the drive gear and the driven gear. At least one of the first meta-lens and the second meta-lens is fixed on the driven gear and rotates together with the driven gear.

12. An imaging system, characterized in that, include: A signal transmitting source, a first zoom lens group, a second zoom lens group, and an imaging detector are arranged sequentially along a selected direction. The first zoom lens group is used to converge the diverging beam of the signal transmitting source to the imaging target, and the second zoom lens group is used to converge the transmitted / reflected beam of the imaging target to the imaging detector. The first zoom lens group and the second zoom lens group are both zoom meta-lens groups as described in any one of claims 1-11.

13. The imaging system according to claim 12, characterized in that, Also includes: A displacement support is disposed between the first zoom lens group and the second zoom lens group. The displacement support is used to support the imaging target and adjust the object distance to present a clear image. The imaging target can move on the displacement support along the selected direction.

Images