Structure, processing method and application of twisted photonic crystal

Abstract

A twisted photonic crystal structure, processing method, and application include a periodic dielectric structure, an embedded metasurface structure, and a substrate. The periodic dielectric structure, as a topological photonic crystal, carries a topological continuum bound state (BIC), exhibiting polarization vortices in momentum space. These polarization vortices originate from the momentum-space topological singularity of the BIC and provide a basis for light field modulation. The embedded metasurface structure, integrated within the periodic dielectric structure and composed of groove structural units, can both reduce disturbances to the light field of the periodic dielectric structure and preserve its inherent topological properties. By twisting the geometric shape of the embedded metasurface structure, the chirality of the circular polarization vortex can be induced, enabling the control of the chirality of the topological continuum bound state; rotating the structure can generate a phase gradient, achieving beam deflection and vortex generation; and the embedded metasurface structure design can realize special points in the Jones matrix, achieving exotic optical effects. This structure has high application value in fields such as light field control and optical device design.

Description

Technical Field

[0001] The present invention relates to photonic crystals and supersurface technology, and in particular to a structure, processing method and application of a twisted photonic crystal. Background Art

[0002] In the field of modern optics, photonic crystals, as dielectric structures with periodically modulated refractive indexes, show great potential for controlling light propagation due to their unique optical properties. They can precisely manipulate the motion of photons, similar to how semiconductors control electrons, and play a key role in many cutting-edge technologies, including optical communications, optical sensing, and optical computing. With the deepening of research, topological photonics has gradually emerged, aiming to utilize topological principles to design and optimize photonic crystals for more efficient and stable control of light. Control of topological boundary states has become a research hotspot. However, conventional photonic crystals have the following limitations in controlling topological boundary states: chiral optical responses primarily rely on intrinsic material properties and lack geometrical control mechanisms; reconfigurable and multi-degree-of-freedom control is difficult to achieve; tunable vortex generation requires complex multilayer structures, and microfabrication of double-layer structures in the optical band is subject to poor tolerance and complexity; and the chirality of vortex polarization based on bound states in the continuous spectrum is structurally limited and currently primarily achieved with single-layer structures, making three-dimensional microfabrication difficult.

[0003] Specifically, traditional photonic crystal and metasurface technologies face the following key technical bottlenecks in topological state regulation:

[0004] Insufficient material dependence and control freedom: Existing chiral optical responses mainly rely on the intrinsic optical activity of the material (such as chiral molecules or anisotropic crystals), and lack the physical mechanism to achieve dynamic chirality control through pure geometric structure, resulting in the device function being rigid and incompatible with standard semiconductor processes.

[0005] The chirality of the vortex polarization of bound states in the continuous spectrum is restricted by the structure: constrained by structural symmetry, the bound states in the traditional topological continuous spectrum only support linearly polarized radiation and cannot produce high-purity circular polarization states (Stokes parameter |S3| is close to 0), which seriously restricts its application in fields such as quantum optics chiral interfaces.

[0006] The control of the quality factor and polarization ellipticity of bound states in the continuous spectrum in the optical band is limited by the processing method of planar optics.

[0007] The contradiction between manufacturing precision and scale: The processing of nano-rotating structures usually requires multi-step electron beam exposure or focused ion beam etching, which has problems such as large angle control error (Δθ>2°) and high periodic structure mismatch rate, making it difficult to meet large-scale integration requirements.

[0008] It should be noted that the information disclosed in the above background technology section is only used to understand the background of this application, and therefore may include information that does not constitute prior art known to ordinary technicians in this field. Summary of the Invention

[0009] The main purpose of the present invention is to overcome the defects in the above-mentioned background technology and provide a structure, processing method and application of a twisted photonic crystal.

[0010] To achieve the above object, the present invention adopts the following technical solutions:

[0011] A twisted photonic crystal structure, comprising:

[0012] The periodic dielectric structure, as a topological photonic crystal, carries a topological continuum bound state (BIC), which exhibits a polarization vortex in momentum space. This polarization vortex originates from the momentum-space topological singularity of the BIC, thereby producing a fundamental modulation effect on the light field.

[0013] An embedded metasurface structure is integrated into the periodic dielectric structure and is composed of groove structural units. Since the groove structural units cause minimal disturbance to the field, while retaining the inherent topological properties of the periodic dielectric structure, the geometric shape of the embedded metasurface structure is twisted to induce circularly polarized vortex chirality, thereby achieving regulation of the chirality of the topological continuous spectrum bound state. By rotating the embedded metasurface structure, a phase gradient is generated through Berry phase accumulation to achieve beam deflection and vortex generation. Through the design of the embedded metasurface structure, an exceptional point (EP) is realized in the Jones matrix, achieving a singular optical effect.

[0014] The substrate carries the periodic dielectric structure and provides physical support for the twisted photonic crystal structure.

[0015] A method for processing twisted photonic crystals adopts single micro-nano processing electron beam lithography (EBL) and reactive ion etching (RIE) technology to simultaneously process a periodic dielectric structure and an adjustable metasurface structure embedded therein to realize twisted photonic crystals.

[0016] An application of the twisted photonic crystal is to apply the twisted photonic crystal to a chiral light source, a vortex generator or an optical sensor chip.

[0017] The present invention has the following beneficial effects:

[0018] The twisted photonic crystal of the present invention exhibits significant technical advantages in many aspects through innovative structural design and processing methods. Structurally, the periodic medium structure works in conjunction with the embedded metasurface structure. The embedded metasurface structure can achieve the functions of controlling the chirality of the topological continuous spectrum bound state, beam deflection and vortex generation, and achieving unique optical effects by twisting the geometric shape, rotation, and specific design without destroying the topological properties of the periodic medium structure, thereby greatly improving the degree of freedom of chirality control. In terms of processing methods, a single micro-nano processing electron beam lithography (EBL) and reactive ion etching (RIE) process is used to synchronously process related structures to realize twisted photonic crystals, avoiding multiple lithography, overlay, and three-dimensional processing. The process has strong compatibility, which not only ensures manufacturing accuracy, but also solves the contradiction between manufacturing accuracy and scale. It can also maintain structural symmetry during processing, obtain a topological vortex radiation state in which the polarization vortex is adjustable with the twist angle (20°-40°) and maintain an extremely high quality factor. In terms of application, it can be widely used in the fields of chiral light sources, vortex generators, optical sensor chips, etc., fundamentally solving the core contradiction between functional reconfigurability, performance limit breakthroughs and large-scale manufacturing in topological photonic devices, and promoting the development and application of topological photonic technology.

[0019] Other beneficial effects of the embodiments of the present invention will be further described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the twisted photonic crystal structure of the present invention according to an embodiment of the present invention.

[0021] Figure 2 1 is a diagram showing the relationship between the torsion angle and the Stokes parameter S3 of the bound state polarization in the continuous spectrum according to an embodiment of the present invention.

[0022] Figure 3 The bound state in the circular polarization continuous spectrum in the embodiment of the present invention when the twist angle is 30 degrees in the momentum space (k x ,k γ ) characteristic diagram. DETAILED DESCRIPTION

[0023] The following is a detailed description of the embodiments of the present invention. It should be emphasized that the following description is only exemplary and is not intended to limit the scope of the present invention and its application.

[0024] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for both fixing and coupling or communication.

[0025] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the embodiments of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0027] See Figure 1 An embodiment of the present invention provides a structure of a twisted photonic crystal, comprising: a periodic dielectric structure 1, serving as a topological photonic crystal, carrying a topological continuous spectrum bound state (BIC), presenting a polarization vortex in momentum space, wherein the polarization vortex originates from the momentum-space topological singularity of the BIC, thereby producing a basic modulation effect on the light field; an embedded metasurface structure 2, integrated into the periodic dielectric structure 1, and composed of groove structure units. Since the groove structure units (twisted holes) cause minimal disturbance to the field, while retaining the inherent topological properties of the periodic dielectric structure 1, the geometric shape of the embedded metasurface structure 2 is twisted to induce the chirality of the circular polarization vortex, thereby achieving the control of the chirality of the topological continuous spectrum bound state; by rotating the embedded metasurface structure 2, a phase gradient is generated through Berry phase accumulation, which is used to achieve beam deflection and vortex generation; through the design of the embedded metasurface structure 2, an exceptional point (EP) is realized in the Jones matrix, achieving a singular optical effect; a substrate 3, carrying the periodic dielectric structure 1, which can provide physical support for the entire twisted photonic crystal structure, ensure the stability of the structure, and facilitate subsequent processing operations. Among them, the periodic medium structure 1 and the embedded metasurface structure 2 cooperate with each other to realize advanced light-matter interaction functions, including chirality control, wavefront engineering, complex vortex beam generation, and provide a basis for the realization of ultra-thin planar optical elements for holographic projection.

[0028] In some embodiments, the periodic medium structure 1 is a square column array, the embedded metasurface structure 2 is a square groove structure unit, and the square groove structure unit is synchronously processed and embedded in the topological photonic crystal composed of the square column array.

[0029] In some embodiments, the rotation angle θ of the embedded metasurface structure 2 ranges from 20° to 40°, and the light field response is regulated by changing the rotation angle θ.

[0030] In some embodiments, the period of the periodic dielectric structure 1 , the side length of the square pillars, and the side length of the holes with twisted grooves can be adjusted to design infinite high quality factor resonance, i.e., bound states in the continuous spectrum.

[0031] A method for processing a twisted photonic crystal adopts a single micro-nano processing electron beam lithography (EBL) and reactive ion etching (RIE) process to simultaneously process a periodic dielectric structure 1 and an adjustable metasurface structure embedded therein to realize a twisted photonic crystal.

[0032] In some embodiments, by controlling the torsion angle of the metasurface structure, a topological vortex radiation state in which the polarization vortex is adjustable with the torsion angle is obtained, and the structural symmetry is maintained to maintain an extremely high quality factor. In a preferred embodiment, the periodic medium structure 1 is a square column array, and the adjustable metasurface structure is a square groove structural unit; the periodic pattern of the square column array and the shape and torsion angle of the square groove structural unit are synchronously defined by electron beam lithography (EBL), and then the defined area is etched by reactive ion etching (RIE) to form synchronously embedded square groove structural units in the square column array, and the structural symmetry is maintained during the processing to obtain a topological vortex radiation state in which the polarization vortex is adjustable with the torsion angle, maintaining an extremely high quality factor.

[0033] An application of the twisted photonic crystal is to apply the twisted photonic crystal to a chiral light source, a vortex generator or an optical sensor chip.

[0034] The structure of the twisted photonic crystal of the present invention realizes the quantitative decoupling control of the chirality (Stokes parameter S3) of the bound state (BIC) in the continuous spectrum by the geometric rotation angle (θ) by introducing a programmable rotating metasurface unit and an asymmetric topological coupling mechanism, and the control has good adjustability. At the same time, there is no need for complex methods such as multiple lithography and overlay, and only a single micro-nano processing electron beam lithography (EBL) and reactive ion etching (RIE) process is used to realize the preparation of the twisted photonic crystal. During the preparation process, this processing method can obtain a topological vortex radiation state in which the polarization vortex is adjustable with the twist angle, and will not break the structural symmetry, thereby maintaining an extremely high quality factor, wherein the preferred range of the θ angle is 20°-40°, and it also supports gradient rotation design and multi-material system expansion.

[0035] From a technical perspective, the present invention significantly enhances the freedom of chirality control, enabling simultaneous manipulation of the polarization and chirality of bound states in the continuous spectrum through geometric parameter twisting (theta angle). Furthermore, it offers strong process compatibility, eliminating the need for three-dimensional, multiple etching processes with a single etching process, effectively simplifying the process flow. In terms of application, the twisted photonic crystals of the present invention exhibit significant scalability, with applications in a variety of applications, including chiral light sources, vortex generators, and optical sensor chips.

[0036] More importantly, the present invention fundamentally resolves the long-standing core contradiction between functional reconfigurability, performance limit breakthroughs and large-scale manufacturing in topological photonic devices, opens up a new path for the development and practical application of topological photonic technology, and has high application value.

[0037] The specific embodiments of the present invention are further described below with reference to the accompanying drawings.

[0038] Figure 1 This is a schematic diagram of the twisted photonic crystal structure of the present invention according to an embodiment of the present invention, showing a periodic medium structure (square column array) as the basis, synchronously processed and embedded adjustable square groove structural units (twisted holes with an angle of θ), presenting the overall architecture of the twisted photonic crystal, and highlighting its basic components and structural relationships. Figure 2 This is a diagram of the regulation relationship between the torsion angle and the Stokes parameter S3 of the bound state polarization in the continuous spectrum in an embodiment of the present invention. The horizontal axis is the torsion angle, and the vertical axis shows the polarization state change (measured by the Stokes parameter S3). It shows that by changing the torsion angle, the polarization state of the bound state in the continuous spectrum can be regulated, covering a variety of polarization states, where S3 = -1 or +1 corresponds to the bound state in the circular polarization continuous spectrum. Figure 3 The bound state in the circular polarization continuous spectrum in the embodiment of the present invention when the twist angle is 30 degrees in the momentum space (k x ,k γ ), which shows the distribution of quality factor, polarization Stokes parameter S3 and polarization angle in momentum space, showing a BIC point close to infinity (bound state in the continuous spectrum), the polarization Stokes parameter S3 around it is close to -1 (corresponding to circular polarization), and the polarization angle has a vortex surround feature, showing a circularly polarized vortex radiation state.

[0039] Example 1:

[0040] The twisted photonic crystal of the embodiment of the present invention is prepared based on electron beam lithography (EBL) and reactive ion etching (RIE) processes. A square column array is used as a periodic dielectric structure (topological photonic crystal), and an adjustable square groove structure unit (twisted hole with a rotation angle θ) is simultaneously processed and embedded in the photonic crystal. The twisted photonic crystal is realized by a single lithography (for example, Figure 1). Usually, bound states in non-linear polarization continuous spectra require three-dimensional micro-nano processing methods. The embodiments of the present invention are realized through single-time planar micro-nano processing, and the light field response is regulated by changing the rotation angle θ, replacing the traditional three-dimensional or multiple processing to realize the function of the torsional photonic crystal. Among them, the angle θ is preferably in the range of 20°-40°, which supports gradient rotation design and multi-material system expansion. In addition, by adjusting the period of the photonic crystal, the side length of the square column, and the side length of the torsional hole, a resonance with infinite high quality factor can be designed (bound state in the continuous spectrum). This processing method is used to obtain a topological vortex radiation state in which the polarization vortex is adjustable with the torsion angle, without breaking the symmetry, thereby maintaining an extremely high quality factor.

[0041] Experimental test:

[0042] Experiments on twisted photonic crystals: rotating the angle of the twisted hole can control the polarization Stokes parameter S3 of the bound state in the continuous spectrum (such as Figure 2 ), the polarization change range covers all polarization states, when S3 = -1 or +1 is the bound state in the circular polarization continuous spectrum. Taking the twist angle of 30° as an example, the bound state in the circular polarization continuous spectrum (such as Figure 3 ). It can be seen that in momentum space (k x ,k γ ), there is a BIC point (bound state in the continuous spectrum) with a quality factor close to infinity, and the surrounding polarization Stokes parameter S3 is close to -1 (corresponding to circular polarization), and the polarization angle shows a vortex-encircling feature, forming a circularly polarized vortex radiation state. This feature has never been achieved in previous designs and applications. The experiment verified the effect of the present invention on synchronously regulating the polarization state and chirality of the bound state in the continuous spectrum by twisting the geometric parameters (θ angle). At the same time, based on a single etching process, the process compatibility is strong, and there is no need for three-dimensional or multiple etchings, which effectively solves the problems existing in traditional photonic crystals and metasurface technologies in topological state regulation.

[0043] In summary, compared with traditional technologies, the present invention has the following significant features and technical advantages:

[0044] (1) The freedom of chirality control is significantly improved: by twisting the geometric parameters (angle θ), the synchronous and precise control of the polarization state and chirality of the bound state in the continuous spectrum is achieved, breaking through the limitations of traditional technology in the control dimension.

[0045] (2) Excellent process compatibility: Relying on a single-etching process, there is no need for three-dimensional processing or multiple etchings, which not only simplifies complex processes but also improves manufacturing efficiency and stability, and is highly adaptable to large-scale production needs.

[0046] (3) Diversified expansion of application scenarios: It has broad application prospects in the field of optoelectronics, covering cutting-edge directions such as chiral light sources, vortex generators, and optical sensor chips, providing core technical support for the innovative design of related devices.

[0047] (4) Solve the core contradictions in the industry: fundamentally solve the contradiction between functional reconfigurability, performance limit breakthroughs and large-scale manufacturing in topological photonic devices, and lay a solid foundation for the practical application and industrial promotion of topological photonic technology.

[0048] The above description further details the present invention in conjunction with specific / preferred embodiments, and the specific implementation of the present invention should not be construed as being limited to these descriptions. Persons skilled in the art will appreciate that, without departing from the spirit of the present invention, they may make various substitutions or modifications to the described embodiments, and these substitutions or modifications should be considered to fall within the scope of protection of the present invention. Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "preferred embodiments," "examples," "specific examples," or "some examples" indicates that the specific features, structures, materials, or characteristics described in conjunction with such embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Persons skilled in the art may combine and assemble the different embodiments or examples described in this specification, as well as features of different embodiments or examples, without conflicting opinions. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications may be made herein without departing from the scope of protection of the patent application.

Claims

1. A twisted photonic crystal structure, characterized in that: include: The periodic dielectric structure, as a topological photonic crystal, carries a topological continuum bound state (BIC), which exhibits a polarization vortex in momentum space. This polarization vortex originates from the momentum-space topological singularity of the BIC, thereby producing a fundamental modulation effect on the light field. An embedded metasurface structure is integrated into the periodic dielectric structure and is composed of groove structural units. While retaining the inherent topological properties of the periodic dielectric structure, it induces circularly polarized vortex chirality by twisting the geometric shape of the embedded metasurface structure, thereby achieving regulation of the chirality of the topological continuous spectrum bound state. By rotating the embedded metasurface structure, a phase gradient is generated through Berry phase accumulation to achieve beam deflection and vortex generation. Through the design of the embedded metasurface structure, an exceptional point (EP) is realized in the Jones matrix, achieving a singular optical effect. The substrate carries the periodic dielectric structure and provides physical support for the twisted photonic crystal structure.

2. The structure of a twisted photonic crystal according to claim 1, characterized in that: The periodic medium structure is a square column array, the embedded metasurface structure is a square groove structure unit, and the square groove structure unit is synchronously processed and embedded in the topological photonic crystal composed of the square column array.

3. The structure of a twisted photonic crystal according to claim 1, characterized in that: The rotation angle θ of the embedded metasurface structure ranges from 20° to 40°, and the light field response is regulated by changing the rotation angle θ.

4. The structure of a twisted photonic crystal according to claim 1, characterized in that: The period of the periodic dielectric structure, the side length of the square pillars, and the side length of the holes twisted by the grooves can be adjusted to design a resonance with an infinite high quality factor, that is, a bound state in a continuous spectrum.

5. A method for processing a twisted photonic crystal according to any one of claims 1 to 4, characterized in that: By using single-shot micro-nanofabrication electron beam lithography (EBL) and reactive ion etching (RIE) processes, the periodic dielectric structure and the adjustable metasurface structure embedded therein are simultaneously processed to realize the twisted photonic crystal.

6. The method for processing a twisted photonic crystal according to claim 5, characterized in that: By controlling the torsion angle of the metasurface structure, a topological vortex radiation state in which the polarization vortex is adjustable with the torsion angle is obtained, and the structural symmetry is maintained to maintain an extremely high quality factor.

7. The method for processing a twisted photonic crystal according to claim 6, characterized in that: The periodic medium structure is a square column array, and the adjustable metasurface structure is a square groove structural unit. The periodic pattern of the square column array and the shape and torsion angle of the square groove structural unit are synchronously defined by electron beam lithography (EBL), and then the defined area is etched by reactive ion etching (RIE) to form synchronously embedded square groove structural units in the square column array. The structural symmetry is maintained during the processing to obtain a topological vortex radiation state in which the polarization vortex is adjustable with the torsion angle, maintaining an extremely high quality factor.

8. Use of the twisted photonic crystal according to any one of claims 1 to 4, characterized in that: The twisted photonic crystal is applied to a chiral light source, a vortex generator or an optical sensor chip.

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