Structure, processing method and application of twisted photonic crystal

Abstract

The invention discloses a structure, a processing method and application of a twisted photonic crystal. The twisted photonic crystal comprises a periodic medium structure, an embedded metasurface structure and a substrate. The periodic medium structure serves as a topological photonic crystal, bears a topological continuous spectrum bound state (BIC) and presents a polarization vortex in a momentum space, and the polarization vortex is derived from a momentum-space topological singular point of the BIC and provides a basis for light field modulation. The embedded metasurface structure is integrated in the periodic medium structure and is composed of groove structure units, disturbance to a light field of the periodic medium structure can be reduced, and inherent topological attributes of the periodic medium structure can be reserved. By twisting the geometrical shape of the embedded metasurface structure, the circularly polarized vortex chirality can be induced, and the regulation and control of the bound state chirality of the topological continuous spectrum can be realized; a phase gradient can be generated by rotating the structure, and light beam deflection and vortex generation are realized; the design of the embedded metasurface structure can realize special points in a Jones matrix and achieve a singular optical effect. The structure has high application value in the fields of light field regulation and control, optical device design and the like.

Description

Technical Field

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

[0002] In the field of modern optics, photonic crystals, as a medium structure with periodically modulated refractive index, show great potential in the regulation of light propagation due to their unique optical properties. It can precisely control the movement of photons like semiconductors control electrons, and plays a key role in many cutting-edge technologies such as optical communications, optical sensing, and optical computing. With the deepening of research, topological photonics has gradually emerged, aiming to use topological principles to design and optimize photonic crystals to achieve more efficient and stable regulation of light, among which topological boundary state regulation has become a research hotspot. However, traditional photonic crystals have the following limitations in the regulation of topological boundary states: chiral optical response mainly depends on the intrinsic properties of the material, lacking geometric freedom control means; it is difficult to achieve reconfigurable and multi-degree-of-freedom regulation; adjustable vortex generation requires complex multi-layer structures, and the process tolerance of double-layer structures in the optical band is poor and complex; the chirality of vortex polarization based on bound states in the continuous spectrum is limited by the structure, and is currently mainly realized in single-layer structures, and three-dimensional micro-nano structures are difficult to process.

[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 vortex polarization of bound states in the continuous spectrum is restricted by the structure: constrained by structural symmetry, bound states in traditional topological continuous spectra 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 is limited by the processing method of planar optics in the optical band.

[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 for understanding the background of the present application, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the invention

[0009] The main purpose of the present invention is to overcome the defects existing 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 continuous spectrum bound state (BIC), presenting a polarization vortex in momentum space. The polarization vortex originates from the momentum-space topological singularity of the BIC, and thus produces a fundamental modulation effect on the light field.

[0013] The embedded metasurface structure is integrated in the periodic medium structure and is composed of groove structure units. Since the groove structure unit has very little disturbance on the field, while retaining the inherent topological properties of the periodic medium structure, the geometric shape of the embedded metasurface structure is twisted to induce the chirality of the circular polarization vortex, thereby realizing the regulation of the chirality of the bound state of the topological continuous spectrum; by rotating the embedded metasurface structure, a phase gradient is generated through Berry phase accumulation to realize beam deflection and vortex generation; through the design of the embedded metasurface structure, a special point (EP) is realized in the Jones matrix to achieve 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 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 and an adjustable metasurface structure embedded therein, thereby realizing a twisted photonic crystal.

[0016] An application of the twisted photonic crystal, wherein the twisted photonic crystal is applied 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 supersurface structure. The embedded supersurface structure can achieve the functions of regulating the chirality of the topological continuous spectrum bound state, beam deflection and vortex generation, and achieving singular optical effects by twisting the geometric shape, rotation, and specific design without destroying the topological properties of the periodic medium structure, greatly improving the chirality control freedom. In terms of processing methods, single-shot micro-nano processing electron beam lithography (EBL) and reactive ion etching (RIE) processes are 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 torsion 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 Graph showing the regulation relationship between the torsion angle and the bound state polarization Stokes parameter S3 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 and application of the present invention.

[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 fixing as well as for coupling or communication.

[0025] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" 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 referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0026] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0027] See also Figure 1 The embodiment of the present invention provides a structure of a twisted photonic crystal, including: a periodic dielectric structure 1, as a topological photonic crystal, carrying a topological continuous spectrum bound state (BIC), presenting a polarization vortex in momentum space, the polarization vortex originating from the momentum-space topological singularity of the BIC, and then producing a basic modulation effect on the light field; an embedded metasurface structure 2, integrated in the periodic dielectric structure 1, composed of groove structure units, because the groove structure unit (twisted hole) has a very small disturbance to the field, while retaining the inherent topological properties of the periodic dielectric structure 1, by twisting the geometric shape of the embedded metasurface structure 2, inducing the chirality of the circular polarization vortex, and realizing the regulation 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 realize beam deflection and vortex generation; through the design of the embedded metasurface structure 2, a special point (EP) is realized in the Jones matrix to achieve 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 of the groove twisting can be adjusted to design a resonance with infinite high quality factor, that is, a bound state 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 structure unit; the periodic pattern of the square column array and the shape and torsion angle of the square groove structure unit are synchronously defined by electron beam lithography (EBL), and then the defined area is etched by reactive ion etching (RIE) to form a synchronously embedded square groove structure unit 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, and maintain an extremely high quality factor.

[0033] An application of the twisted photonic crystal, wherein the twisted photonic crystal is applied 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 geometric rotation angle (θ) on the chirality (Stokes parameter S3) of the bound state (BIC) in the continuous spectrum 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 achieve the preparation of the twisted photonic crystal. During the preparation process, this processing method can be used to obtain a topological vortex radiation state in which the polarization vortex is adjustable with the torsion angle, and the structural symmetry will not be broken, thereby maintaining an extremely high quality factor, wherein the preferred range of the θ angle is 20°-40°, and gradient rotation design and multi-material system expansion are also supported.

[0035] From the perspective of technical advantages, on the one hand, the present invention greatly improves the degree of freedom of chirality control, and can synchronously control the polarization state and chirality of bound states in the continuous spectrum through geometric parameter twisting (θ angle); on the other hand, it has strong process compatibility, and the single etching processing method abandons three-dimensional and multiple etching, effectively simplifying the process flow. In the application field, the twisted photonic crystal of the present invention shows significant scalability and can be applied to many aspects such as chiral light sources, vortex generators, and optical sensor chips.

[0036] What is particularly important is that the present invention fundamentally solves the long-standing core contradiction between functional reconfigurability, performance limit breakthrough 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 of an embodiment of the present invention. The horizontal axis is the torsion angle, and the vertical axis shows the change in polarization state (measured by the Stokes parameter S3). It shows that the polarization state of the bound state in the continuous spectrum can be regulated by changing the torsion angle, 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, presenting a BIC point close to infinity (bound state in the continuous spectrum), with the polarization Stokes parameter S3 around it close to -1 (corresponding to circular polarization), and the polarization angle has a vortex surround feature, showing a vortex radiation state of circular polarization.

[0039] Embodiment 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 medium 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 (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 twisted photonic crystals. Among them, the preferred range of the angle θ is 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 torsion hole, a resonance (bound state in the continuous spectrum) with infinite high quality factor can be designed. 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: By rotating the angle of the twisted hole, the polarization Stokes parameter S3 of the bound state in the continuous spectrum can be controlled (e.g. Figure 2 ), the polarization change range covers all polarization states, and when S3 = -1 or +1, it is the bound state in the circular polarization continuum. Taking the twist angle of 30° as an example, the bound state in the circular polarization continuum (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 surround feature, forming a circularly polarized vortex radiation state, a feature that has never been achieved in previous designs and applications. The experiment verifies the effect of the present invention on synchronously regulating the polarization state and chirality of bound states 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 no three-dimensional or multiple etching is required, which effectively solves the problems existing in the topological state regulation of traditional photonic crystals and metasurface technologies.

[0043] In summary, compared with the traditional technology, 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 breakthrough 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 content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, it can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of the reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. 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 can 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 continuous spectrum bound state (BIC), presenting a polarization vortex in momentum space. The polarization vortex originates from the momentum-space topological singularity of the BIC, and thus produces a fundamental modulation effect on the light field. The embedded metasurface structure is integrated in the periodic medium structure and is composed of groove structure units. While retaining the inherent topological properties of the periodic medium structure, it induces circular polarization vortex chirality by twisting the geometric shape of the embedded metasurface structure, thereby achieving regulation of the chirality of the bound state of the topological continuous spectrum; 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, a special point (EP) is realized in the Jones matrix to achieve 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 super surface 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: The twisted photonic crystal is realized by using single-shot micro-nanofabrication electron beam lithography (EBL) and reactive ion etching (RIE) processes to simultaneously process the periodic dielectric structure and the adjustable metasurface structure embedded therein.

6. A 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. A 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, 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, thereby maintaining an extremely high quality factor.

8. An application 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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