Electromagnetic field localization enhancement structure based on bilayer film and side-polished perovskite fiber

Abstract

This invention discloses an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber, comprising: a side-polished single-crystal organometallic perovskite optical fiber, a single-layer graphene film, an alumina film, and a titanium dioxide film; the single-layer graphene film, alumina film, and titanium dioxide film are sequentially disposed above the polished surface of the side-polished single-crystal organometallic perovskite optical fiber; the interaction between the fiber mode and the single-layer graphene in the side-polished single-crystal organometallic perovskite optical fiber is achieved based on the double-layer film structure composed of the alumina film and titanium dioxide film with successively increasing refractive indices, thereby realizing the localization enhancement of the electromagnetic field at the graphene; the localization enhancement effect of the electromagnetic field at the graphene is modulated by controlling the thickness of the double-layer film of alumina film and titanium dioxide film deposited on the side-polished single-crystal organometallic perovskite optical fiber with transferred single-layer graphene. This invention enables efficient interaction between the transmitted optical field in the fiber core and two-dimensional materials, providing a framework for integrating high-performance photodetectors, sensors, and nonlinear devices on perovskite optical fibers.

Description

Technical Field

[0001] This invention relates to the field of fiber optic integrated devices and electromagnetic field localization enhancement microstructures, specifically to an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber. Background Technology

[0002] In recent years, the integration of two-dimensional materials with fiber optic devices has become a research hotspot in the interdisciplinary field of materials science and micro-nano optoelectronics. Thanks to the excellent optoelectronic and mechanical properties of two-dimensional materials, they can be integrated with various types of optical fibers, expanding the application scenarios of fiber optic devices to numerous fields, such as fiber optic photodetectors, fiber optic modulators, fiber optic sensors, and fiber optic nonlinear devices. Achieving efficient coupling between fiber optic modes and two-dimensional materials is a prerequisite for realizing high-performance fiber optic devices.

[0003] Graphene has attracted widespread attention from researchers due to its excellent optical properties, high carrier mobility, and high thermal conductivity. However, the ultra-small size and atomic-layer thickness of monolayer graphene result in a small light absorption area and low light absorption rate (2.3%), posing a significant challenge to the interaction between light and monolayer graphene. Currently, effective solutions include using resonance effects, metal reflection, or combining with waveguides, such as a fiber-optic integrated photodetector with polarization function (patent publication number CN113865702A), which increases light absorption by extending the interaction distance between light and graphene. However, the core diameter of ordinary single-mode optical fiber is only 8 μm, so millimeter-level interaction distances are typically required to increase the effective interaction area.

[0004] Single-crystal organometallic perovskite optical fibers possess advantages such as high stability, low optical transmission loss, long carrier lifetime, and excellent third-order nonlinear optical properties, making them ideal materials for fabricating semiconductor-core optical fibers. Currently, various methods for fabricating single-crystal organometallic perovskite optical fibers have been reported, such as: cooling crystallization, solvent vapor-assisted crystallization, liquid diffusion separation-induced crystallization, and reverse temperature crystallization. These single-crystal organometallic perovskite optical fibers have a core of single-crystal organometallic perovskite and a cladding of silicon dioxide or tetrafluoroethylene, exhibiting a low transmission loss of <0.7 dB / cm, and a core diameter reaching hundreds of micrometers (Zhou Y, Parkes MA, Zhang J, et al. Single-crystal organometallic perovskite optical fibers[J]. Science Advances, 2022, 8(38): eabq8629.). The large core diameter is beneficial for increasing the interaction area between light and matter and for reducing the difficulty of fiber integration, making it an ideal advanced functional fiber platform for fabricating light sources, detectors, sensors, and nonlinear optical devices. According to the principle of total internal reflection in optical fibers, light always propagates in the core with a high refractive index, while the cladding with a lower refractive index confines the light. Before polishing, single-crystal organometallic perovskite fibers satisfy the condition for total internal reflection, with light propagating in the high-refractive-index core. After polishing, the removal of one side of the silica cladding exposes the core to air, allowing the evanescent field to leak from the polished surface and interact with the external environment. By covering the polished surface with different functional materials, detection and sensing functions can be achieved. Currently, the integration technology of single-crystal organometallic perovskite fibers with two-dimensional materials has not been studied. Furthermore, the refractive index of single-crystal organometallic perovskite (n = 1.9841, @1600nm) is much greater than that of two-dimensional materials such as graphene and molybdenum disulfide. Achieving efficient interaction between the light field propagating in the core and the two-dimensional material is a challenge for realizing high-performance perovskite fiber devices. Summary of the Invention

[0005] To overcome the defects and shortcomings of existing technologies, this invention provides an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber. This invention utilizes an aluminum oxide (Al₂O₃) / titanium dioxide (TiO₂) double-layer film structure with sequentially increasing refractive indices to achieve efficient interaction between the fiber mode and monolayer graphene in a side-polished single-crystal organometallic perovskite optical fiber, thereby achieving localized enhancement of the electromagnetic field at the graphene. By controlling the thickness of the aluminum oxide (Al₂O₃) / titanium dioxide (TiO₂) double-layer film deposited on the side-polished single-crystal organometallic perovskite optical fiber with transferred monolayer graphene, the localized enhancement effect of the electromagnetic field at the graphene is modulated, providing an effective solution for improving the light absorption coefficient of monolayer graphene. Using titanium dioxide as a humidity-sensitive material, this structure provides a supporting basis for realizing highly sensitive fiber humidity sensing and photoelectric detection on perovskite optical fibers.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides an electromagnetic field localization enhancement structure based on a double-layer film and a side-polished perovskite optical fiber, comprising: a side-polished single-crystal organometallic perovskite optical fiber, a single-layer graphene film, an aluminum oxide film, and a titanium dioxide film.

[0008] The single-layer graphene film, aluminum oxide film, and titanium dioxide film are sequentially arranged above the polished surface of the side-polished single-crystal organometallic perovskite optical fiber.

[0009] A double-layer film structure composed of aluminum oxide and titanium dioxide films with successively increasing refractive indices is used to realize the interaction between the fiber mode and the single-layer graphene in the side-polished single-crystal organometallic perovskite optical fiber, thereby locally enhancing the intensity of the electromagnetic field at the graphene.

[0010] By controlling the thickness of the bilayer film composed of aluminum oxide and titanium dioxide films deposited on a side-polished single-crystal organometallic perovskite optical fiber with transferred monolayer graphene, the local enhancement effect of the electromagnetic field at the graphene can be modulated.

[0011] As a preferred technical solution, the side-polished single-crystal organometallic perovskite optical fiber includes a silica cladding and a single-crystal organometallic perovskite core. The single-crystal organometallic perovskite core is encased within the silica cladding, with a portion of the single-crystal organometallic perovskite core exposed outside the silica cladding. The exposed portion of the single-crystal organometallic perovskite core is the polishing area, which has a planar structure. The unpolished lower surface of the optical fiber has an arc-shaped structure. The single-layer graphene film, aluminum oxide film, and titanium dioxide film are sequentially covered on the polishing area.

[0012] As a preferred technical solution, the diameter of the single-crystal organometallic perovskite fiber core is 10-300 μm, and / or the thickness of the silicon dioxide cladding is 10-200 μm.

[0013] As a preferred technical solution, the thickness of the aluminum oxide film is 0-50 nm.

[0014] As a preferred technical solution, the thickness of the titanium dioxide film is 160–200 nm.

[0015] As a preferred technical solution, the longest distance from the polished upper surface to the unpolished lower surface of the side-polished single-crystal organometallic perovskite fiber is the remaining thickness of the side-polished single-crystal organometallic perovskite fiber, and the remaining thickness of the side-polished single-crystal organometallic perovskite fiber is 20% to 70% of the fiber diameter when it is not polished.

[0016] As a preferred technical solution, the refractive index of the titanium dioxide thin film is greater than that of the single-crystal organometallic perovskite fiber core.

[0017] This invention also provides a method for fabricating an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber, comprising the following steps:

[0018] To prepare side-polished single-crystal organometallic perovskite optical fibers, one side of the fiber is polished using a wheel polishing method or a V-groove assisted polishing method, exposing part of the single-crystal organometallic perovskite core to air. After polishing, the fiber is cleaned with an alcohol solution to remove impurities and then passivated with an isopropanol solution to produce side-polished single-crystal organometallic perovskite optical fibers with different remaining thicknesses.

[0019] Transfer a single-layer graphene film to the polished surface of the prepared side-polished single-crystal organometallic perovskite optical fiber.

[0020] Alumina thin film is deposited onto the polished surface of a single-crystal organometallic perovskite optical fiber covered with a single-layer graphene film.

[0021] A titanium dioxide thin film is coated or deposited onto the polished surface of a single-crystal organometallic perovskite optical fiber that is covered with a single-layer graphene film and an aluminum oxide film.

[0022] As a preferred technical solution, the preparation method of single-layer graphene film is one of the following: microcomputer exfoliation method, chemical vapor deposition method, and silicon carbide epitaxial growth method;

[0023] The transfer method for single-layer graphene films is one of the following: direct growth method, polymethyl methacrylate film-assisted wet transfer method, or polydimethylsiloxane film-assisted dry transfer method.

[0024] As a preferred technical solution, the preparation method of aluminum oxide thin film is one of the following: vacuum resistance heating evaporation, electron beam evaporation, magnetron sputtering deposition, pulsed laser deposition, chemical vapor deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, and sol-gel method.

[0025] The titanium dioxide thin film is prepared by one of the following methods: vacuum resistance heating evaporation, electron beam evaporation, magnetron sputtering deposition, pulsed laser deposition, chemical vapor deposition, atomic layer deposition, or sol-gel method.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0027] The present invention features a simple fabrication method and a compact structure. Local field enhancement in the near-infrared band can be achieved using a micron-level fiber polishing length. A method for efficient interaction between the fiber mode and monolayer graphene in a side-polished single-crystal organometallic perovskite fiber is achieved using a bilayer aluminum oxide (Al₂O₃) / titanium dioxide (TiO₂) film structure with progressively increasing refractive indices. This results in localized enhancement of the electromagnetic field at the graphene. By controlling the thickness of the Al₂O₃ / TiO₂ bilayer film deposited on the side-polished single-crystal organometallic perovskite fiber with transferred monolayer graphene, the localized enhancement effect of the electromagnetic field at the graphene can be modulated. This provides an effective solution for improving the light absorption coefficient of monolayer graphene. Furthermore, as titanium dioxide is a humidity-sensitive material, this structure provides a basis for achieving highly sensitive fiber humidity sensing and photoelectric detection on perovskite fibers. This technology can be extended to other two-dimensional materials besides graphene, enabling high-performance perovskite fiber integrated devices that meet the trends of multifunctionality and miniaturization, and has broad application prospects. Attached Figure Description

[0028] Figure 1 This is a cross-sectional schematic diagram of the electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to the present invention.

[0029] Figure 2 This is a comparison diagram of the optical field distribution of the present invention under the same remaining fiber thickness and different device structures.

[0030] Figure 3 This is a normalized optical field intensity diagram along the middle white dashed line, showing the optical field distribution of the present invention under the same fiber remaining thickness and different device structures.

[0031] Figure 4 This is a schematic diagram showing the effect of the thickness of the double-layer hybrid film on the imaginary part of the effective refractive index in the TM mode according to the present invention.

[0032] Figure 5This is a schematic diagram comparing the local field distribution of the present invention under the same fiber remaining thickness and different titanium dioxide film thicknesses.

[0033] Among them, 1-silicon dioxide cladding, 2-single-crystal organometallic perovskite core, 3-single-layer graphene film, 4-alumina film, and 5-titanium dioxide film. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Some components in the drawings may be omitted, enlarged, or reduced, and do not represent actual device dimensions. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0035] Example 1

[0036] like Figure 1 As shown, this embodiment provides an electromagnetic field localization enhancement structure based on a double-layer film and a side-polished perovskite optical fiber, which includes, from bottom to top, the following: a side-polished single-crystal organometallic perovskite optical fiber, a single-layer graphene film 3, an aluminum oxide (Al2O3) film 4, and a titanium dioxide (TiO2) film 5.

[0037] The side-polished single-crystal organometallic perovskite optical fiber includes a silica cladding 1 and a single-crystal organometallic perovskite core 2. The core is made of single-crystal organometallic perovskite (MAPbBr3), and its diameter is 10–300 μm, preferably 100 μm. In this embodiment, the cladding thickness of the silica cladding 1 is 10–200 μm, preferably 20 μm. Of course, the cladding material can also be tetrafluoroethylene (C2F4). The single-crystal organometallic perovskite core 2 is encased within the cladding, and a portion of the single-crystal organometallic perovskite core 2 is exposed above the silica cladding. 1. The exposed part of the fiber core is the polished area, which faces upward and is a flat plane. The unpolished lower surface has an arc-shaped structure. The cross-section of the entire side-polished single-crystal organometallic perovskite fiber is similar to a side-placed "D" shape. The longest distance from the polished area to its lower surface is the remaining thickness of the side-polished perovskite fiber. The single-layer graphene film 3, the alumina film 4, and the titanium dioxide film 5 are successively and tightly covered on the polished area exposed by the fiber core. After the perovskite fiber is polished, the evanescent field leaks from the fiber polishing area. Under the action of the alumina / titanium dioxide double film, the light field is attracted to the vicinity of the single-layer graphene and absorbed by the graphene.

[0038] In this embodiment, the preparation method of the monolayer graphene film is one of the following: microcomputer exfoliation, chemical vapor deposition (CVD), and silicon carbide epitaxial growth; the transfer method of the monolayer graphene film is one of the following: direct growth, polymethyl methacrylate (PMMA) film-assisted wet transfer, and polydimethylsiloxane (PDMS) film-assisted dry transfer.

[0039] Specifically, taking the microcomputer exfoliation method as an example, the graphene prepared by this method has the characteristics of high quality, no chemical pollution, and few defects. The specific steps are as follows:

[0040] (1) Take a piece of high-quality graphite crystal grown by chemical vapor deposition and place it in an inert gas environment for 30 minutes to pretreat the graphite crystal. Use 3M tape to tear off a small piece of graphite crystal. Take another clean piece of 3M tape and stick it to the 3M tape with the small piece of graphite crystal attached. Then tear it off quickly. Repeat this step more than 5 times to obtain single-layer, few-layer or even multi-layer graphene nanosheets.

[0041] (2) The graphene nanosheets were picked up from 3M tape using a 500μm thick medium-viscosity polydimethylsiloxane (PDMS) film and observed under a microscope to find large-area, flat single-layer graphene nanosheets.

[0042] (3) Using a two-dimensional material transfer platform, high-quality monolayer graphene nanosheets are transferred to the polishing area of ​​the side-polished single-crystal organometallic perovskite optical fiber. The heating function of the two-dimensional material transfer platform is activated, the temperature is set to 80℃, and the heating time is 10 minutes, so that the PDMS film loses its adhesiveness. The PDMS film is removed to complete the release of the monolayer graphene nanosheets, and the transfer is completed.

[0043] In this embodiment, the aluminum oxide thin film is prepared by one of the following methods: vacuum resistance heating evaporation, electron beam evaporation, magnetron sputtering deposition, pulsed laser deposition, chemical vapor deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, and sol-gel method. The thickness of the aluminum oxide thin film is 0-50 nm.

[0044] In this embodiment, the titanium dioxide thin film is prepared by one of the following methods: vacuum resistance heating evaporation, electron beam evaporation, magnetron sputtering deposition, pulsed laser deposition, chemical vapor deposition, atomic layer deposition, and sol-gel method. The thickness of the titanium dioxide thin film is 160-200 nm.

[0045] In this embodiment, the refractive index of the titanium dioxide thin film at a wavelength of 1600 nm is 2.4299+0.0001, and the refractive index of the single-crystal organometallic perovskite fiber core at a wavelength of 1600 nm is 1.9841+0.02068i. It can be seen that the real part of the refractive index of the titanium dioxide thin film is greater than the real part of the refractive index of the single-crystal organometallic perovskite fiber core, and the refractive index distribution satisfies the condition that light always propagates in a medium with a high refractive index.

[0046] In this embodiment, the polished upper surface of the side-polished single-crystal organometallic perovskite fiber has a planar structure, and the polishing zone length is 5-5000 μm. The unpolished lower surface of the side-polished single-crystal organometallic perovskite fiber has an arc-shaped structure. The longest distance from the polished upper surface to the unpolished lower surface of the side-polished single-crystal organometallic perovskite fiber is the remaining thickness of the side-polished single-crystal organometallic perovskite fiber. The remaining thickness of the side-polished single-crystal organometallic perovskite fiber is 20%-70% of the fiber diameter when it is not polished. This embodiment uses side-polished single-crystal organometallic perovskite fibers with remaining thicknesses of 65 μm and 70 μm as examples for illustration.

[0047] In this embodiment, a wheel polishing method is used to polish away part of the single-crystal organometallic perovskite fiber core 2 and silicon dioxide cladding 1 to obtain a side-polished single-crystal organometallic perovskite optical fiber; a microcomputer exfoliation method is used to peel off graphite crystals to obtain a single layer of graphene, and a 500 μm thick medium-viscosity polydimethylsiloxane (PDMS) film is used to transfer the single layer of graphene to the polishing area using a heat release method (temperature set at 80°C, heating time 10 minutes). Dry transfer can avoid the influence of chemical residues on the optical and electrical properties of graphene, reduce defects, and improve the graphene transfer quality. Then, an aluminum oxide film and a titanium dioxide film are sequentially deposited on the polishing area using a vacuum resistance heating evaporation method.

[0048] Specifically, the preparation process is as follows:

[0049] Step 1: Preparation of side-polished single-crystal organometallic perovskite fiber: A section of grown single-crystal organometallic perovskite fiber is polished on one side using a wheel polishing method or a V-groove assisted polishing method to remove part of the fiber cladding and core, exposing the single-crystal organometallic perovskite core to the air. After polishing, the fiber is cleaned with an alcohol solution to remove impurities and then passivated with an isopropanol solution to reduce surface defects, thus producing side-polished single-crystal organometallic perovskite fibers with different remaining thicknesses.

[0050] Step 2: Transfer the monolayer graphene film over the polished surface of the side-polished single-crystal organometallic perovskite optical fiber prepared in Step 1.

[0051] Step 3: Deposit a high-quality aluminum oxide film onto the polished surface of the single-crystal organometallic perovskite optical fiber covered with a single-layer graphene film obtained in Step 2.

[0052] Step 4: Coat or deposit a high-quality titanium dioxide film onto the polished surface of the single-crystal organometallic perovskite optical fiber obtained in Step 3, which is covered with a single-layer graphene film and an aluminum oxide film.

[0053] like Figure 2 and Figure 3 As shown, the above model structure was established using the Comsol finite element analysis method and simulation analysis was performed. Since the refractive index of single-crystal organometallic perovskite is much greater than that of single-layer graphene, the simulation confirmed that the optical field distribution of the side-polished single-crystal organometallic perovskite optical fiber is mainly concentrated in the fiber core. After covering with a single layer of graphene, the optical field of the optical fiber is still concentrated in the fiber core. At this time, the evanescent field leaked in the polished area of ​​the optical fiber interacts with the graphene. The interaction strength is weak, making it difficult to achieve highly sensitive photoelectric detection and sensing. After depositing an aluminum oxide / titanium dioxide bilayer film, the high refractive index bilayer film attracts the optical field originally in the fiber core to the vicinity of the graphene. The local field strength at the graphene is greatly enhanced. At this time, the fiber TM mode is efficiently coupled with the graphene, and the light-material interaction strength and light absorption coefficient are greatly enhanced.

[0054] like Figure 4 As shown, the effects of the thicknesses of the alumina and titanium dioxide films on the imaginary part of the effective refractive index in the TM mode are illustrated under the condition that the remaining thickness of the side-polished single-crystal organometallic perovskite fiber is 65 μm. The maximum thickness of the alumina film is 50 nm, and the maximum thickness of the titanium dioxide film is 200 nm. Figure 4 The size of the solid dot represents the size of the imaginary part of the effective refractive index in TM mode, with a maximum imaginary part value of 0.020302 (@10nm aluminum oxide and 170nm titanium dioxide). For example... Figure 4 As shown by the solid dots, under the local field enhancement condition of TM mode, the thickness of the titanium dioxide film increases with the increase of the aluminum oxide film thickness. The results show that bilayer films with different thickness ratios can achieve different degrees of light absorption. Therefore, the local field enhancement effect near monolayer graphene can be controlled by designing the thickness of the bilayer film.

[0055] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm. The thicknesses of the aluminum oxide film and titanium dioxide film on the single-layer graphene film are 5 nm and 170 nm, respectively, and their refractive indices at a wavelength of 1600 nm are 1.6139 and 2.4299+0.0001, respectively. By utilizing the Al2O3 / TiO2 bilayer film with gradually increasing refractive index, the light field originally concentrated in the middle of the fiber core can be attracted to the vicinity of the graphene layer in TM mode. At this time, the electromagnetic field at the graphene position is enhanced from the original 33.33 V / m to 812.7 V / m, and the interaction strength (i.e., the electromagnetic field strength corresponding to the graphene layer position) is enhanced by 24.38 times. The light absorption coefficient under this structure reaches 0.67 dB / μm.

[0056] More specifically, the light absorption coefficient α is calculated using formula 1-1:

[0057]

[0058] Where λ is the wavelength of the incident light, Im(n eff ) represents the imaginary part of the effective refractive index of the mode.

[0059] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm, and the thicknesses of the alumina film and titanium dioxide film are 10 nm and 170 nm, respectively. Their refractive indices at a wavelength of 1600 nm are 1.6139 and 2.4299+0.0001, respectively. By utilizing the bilayer Al2O3 / TiO2 hybrid film with gradually increasing refractive index, the light field originally concentrated in the middle of the fiber core can be attracted to the vicinity of the graphene layer in TM mode. At this time, the electromagnetic field at the graphene location is enhanced from the original 33.33 V / m to 835.73 V / m, and the interaction strength is enhanced by 25.07 times. The light absorption coefficient under this structure reaches 0.69 dB / μm, and the efficient light absorption of single-layer graphene can be achieved with an interaction length at the micron level.

[0060] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm, and the thicknesses of the aluminum oxide film and titanium dioxide film are 20 nm and 180 nm, respectively. Their refractive indices at a wavelength of 1600 nm are 1.6139 and 2.4299+0.0001, respectively. By utilizing the Al2O3 / TiO2 bilayer film with gradually increasing refractive index, the light field originally concentrated in the middle of the fiber core can be attracted to the vicinity of the graphene layer in TM mode. At this time, the electromagnetic field at the graphene location is enhanced from the original 33.33 V / m to 776.94 V / m, and the interaction strength is enhanced by 23.31 times. The light absorption coefficient under this structure reaches 0.66 dB / μm.

[0061] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm, and the thicknesses of the aluminum oxide film and titanium dioxide film are 40 nm and 190 nm, respectively. By utilizing the Al2O3 / TiO2 bilayer film with gradually increasing refractive index, the light field originally concentrated in the middle of the fiber core can be attracted to the vicinity of the graphene layer in TM mode, thereby enhancing the field strength at the graphene layer location by 22.72 times.

[0062] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 70 μm, and the thicknesses of the alumina film and titanium dioxide film are 10 nm and 170 nm, respectively. Their refractive indices at a wavelength of 1600 nm are 1.6139 and 2.4299+0.0001, respectively. At this time, the electromagnetic field at the graphene location is enhanced from the original 29.26 V / m to 761 V / m, and the interaction strength is enhanced by 26 times. The light absorption coefficient of this structure reaches 0.692 dB / μm.

[0063] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 70 μm, and the thicknesses of the alumina film and titanium dioxide film are 40 nm and 190 nm, respectively. Their refractive indices at a wavelength of 1600 nm are 1.6139 and 2.4299+0.0001, respectively. At this time, the electromagnetic field at the graphene location is enhanced from the original 29.26 V / m to 731.8 V / m, and the interaction strength is enhanced by 25.01 times. The light absorption coefficient of this structure reaches 0.68 dB / μm.

[0064] Preferably, the local enhancement effect of the electromagnetic field is optimal when the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 70 μm, and the thicknesses of the alumina film and titanium dioxide film are 10 nm and 170 nm, respectively. Furthermore, this device structure is sensitive to changes in the external refractive index; when the effective coverage length of the device is 100 μm, its sensitivity can reach 27.77 dB / RIU.

[0065] In this embodiment, the TiO2 film attracts the light field in the optical fiber to the vicinity of the TiO2 film, and the 10nm Al2O3 film serves as a reflective film to increase the back-and-forth reflection of the light field between the Al2O3 film and the optical fiber, resulting in a significant localized enhancement of the electromagnetic field near the monolayer graphene. Furthermore, the localized enhancement effect of the electromagnetic field near the monolayer graphene can be controlled by optimizing the design of the remaining thickness of the optical fiber and the thickness ratio of the Al2O3 / TiO2 bilayer film.

[0066] The fabrication method of this invention is simple and the structure is compact. Local field enhancement in the near-infrared band can be achieved using fiber polishing lengths at the micron level. The technical method of this invention can be extended to other two-dimensional materials besides graphene, realizing high-performance perovskite fiber integrated devices that meet the development trends of multifunctionality and miniaturization, and has broad application prospects.

[0067] Example 2

[0068] This embodiment discloses an electromagnetic field localization enhancement structure based on a titanium dioxide thin film and a side-polished perovskite optical fiber, comprising: from bottom to top, a side-polished single-crystal organometallic perovskite optical fiber, a single-layer graphene thin film, and a titanium dioxide thin film, wherein the side-polished single-crystal organometallic perovskite optical fiber includes a silicon dioxide cladding and a single-crystal organometallic perovskite fiber core. The difference between Embodiment 2 and Embodiment 1 is that Embodiment 2 is a field enhancement structure based on a single-layer titanium dioxide thin film, while Embodiment 1 is a field enhancement structure based on an aluminum oxide / titanium dioxide bilayer film.

[0069] Specifically, the core diameter of the single-crystal organometallic perovskite optical fiber is 100 μm, and the thickness of the silica cladding is 20 μm. Half of the core and cladding are polished away using a wheel polishing method to obtain a side-polished single-crystal organometallic perovskite optical fiber with a remaining thickness of 65 μm. Graphite crystals are peeled off using a microcomputer-based exfoliation method to obtain a single layer of graphene. A 500 μm thick medium-viscosity polydimethylsiloxane (PDMS) film is used, and the single layer of graphene is transferred to the polishing area using a thermal release method (temperature set at 80℃, heating time 10 minutes). Dry transfer can avoid the influence of chemical residues on the optical and electrical properties of graphene, reduce defects, and improve the graphene transfer quality. Then, a titanium dioxide film is deposited on the polishing area using a vacuum resistance heating evaporation method.

[0070] like Figure 5 As shown, the above model structure was established using the Comsol finite element analysis method. Simulation confirmed that as the thickness of the titanium dioxide film increases, the light field transmitted in the fiber core gradually concentrates near the polished surface. Furthermore, by optimizing the thickness of the titanium dioxide film, the interaction intensity between light and graphene can be optimized.

[0071] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm, and the thickness of the titanium dioxide film deposited on the single-layer graphene film is 160 nm. The refractive index at a wavelength of 1600 nm is 2.4299+0.0001. At this time, the optical field distribution in the fiber core gradually concentrates near the polished surface, and the electromagnetic field at the graphene position is enhanced from the original 33.33 V / m to 470 V / m. The interaction strength (i.e., the field strength corresponding to the graphene layer position) is enhanced by 14.1 times.

[0072] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm, and the thickness of the titanium dioxide film deposited on the monolayer graphene film is 170 nm. The refractive index at a wavelength of 1600 nm is 2.4299 + 0.0001. At this time, the fiber TM mode is efficiently coupled with the graphene, and the electromagnetic field is localized near the graphene position. The magnitude of the electromagnetic field is enhanced from the original 33.33 V / m to 829.5 V / m, and the interaction strength is enhanced by 24.89 times, realizing the efficient interaction between the fiber mode and the monolayer graphene.

[0073] Specifically, the remaining thickness of the side-polished single-crystal organometallic perovskite optical fiber is 65 μm, and the thickness of the titanium dioxide film deposited on the single-layer graphene film is 180 nm. The refractive index at a wavelength of 1600 nm is 2.4299 + 0.0001. At this time, the field strength at the graphene location is periodically enhanced. The electromagnetic field at the graphene location is enhanced from the original 33.33 V / m to a maximum of 64.4 V / m, and the interaction strength is enhanced by 1.93 times.

[0074] Preferably, in the device structure where a single-layer titanium dioxide film enhances the interaction between graphene and side-polished perovskite optical fiber, the local field enhancement effect near the graphene is optimal when the remaining thickness of the optical fiber is 65 μm and the thickness of the titanium dioxide film is 170 nm.

[0075] According to Examples 1 and 2 above, with the same remaining fiber thickness and the same titanium dioxide film thickness, depositing 10 nm of aluminum oxide before depositing the titanium dioxide film can enhance the reflection of light in the aluminum oxide and fiber core, and further enhance the field localization effect.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber, characterized in that, include: Side-polished single-crystal organometallic perovskite optical fibers, single-layer graphene films, aluminum oxide films, and titanium dioxide films; The single-layer graphene film, aluminum oxide film, and titanium dioxide film are sequentially arranged above the polished surface of the side-polished single-crystal organometallic perovskite optical fiber. A double-layer film structure composed of aluminum oxide and titanium dioxide films with successively increasing refractive indices is used to realize the interaction between the fiber mode and the single-layer graphene in the side-polished single-crystal organometallic perovskite optical fiber, thereby locally enhancing the intensity of the electromagnetic field at the graphene. By controlling the thickness of the bilayer film composed of aluminum oxide and titanium dioxide films deposited on a side-polished single-crystal organometallic perovskite optical fiber with transferred monolayer graphene, the local enhancement effect of the electromagnetic field at the graphene can be modulated.

2. The electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 1, characterized in that, The side-polished single-crystal organometallic perovskite optical fiber includes a silica cladding and a single-crystal organometallic perovskite core. The single-crystal organometallic perovskite core is encased within the silica cladding, with a portion of the single-crystal organometallic perovskite core exposed outside the silica cladding. The exposed portion of the single-crystal organometallic perovskite core is the polishing area, which has a planar structure. The unpolished lower surface of the optical fiber has an arc-shaped structure. The single-layer graphene film, aluminum oxide film, and titanium dioxide film are sequentially covered on the polishing area.

3. The electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 2, characterized in that, The diameter of the single-crystal organometallic perovskite fiber core is 10~300μm, and the thickness of the silicon dioxide cladding is 10~200μm.

4. The electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 1, characterized in that, The thickness of the aluminum oxide film is 5~50 nm.

5. The electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 1, characterized in that, The thickness of the titanium dioxide film is 160 ~ 200 nm.

6. The electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 1, characterized in that, The longest distance from the polished upper surface to the unpolished lower surface of a side-polished single-crystal organometallic perovskite fiber is the remaining thickness of the side-polished single-crystal organometallic perovskite fiber. The remaining thickness of the side-polished single-crystal organometallic perovskite fiber is 20% to 70% of the fiber diameter when it is not polished.

7. The electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 1, characterized in that, The refractive index of the titanium dioxide thin film is greater than that of the single-crystal organometallic perovskite fiber core.

8. The method for fabricating an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to any one of claims 1-7, characterized in that, Includes the following steps: To prepare side-polished single-crystal organometallic perovskite optical fibers, one side of the fiber is polished using a wheel polishing method or a V-groove assisted polishing method, exposing part of the single-crystal organometallic perovskite core to air. After polishing, the fiber is cleaned with an alcohol solution to remove impurities and then passivated with an isopropanol solution to produce side-polished single-crystal organometallic perovskite optical fibers with different remaining thicknesses. Transfer a single-layer graphene film to the polished surface of the prepared side-polished single-crystal organometallic perovskite optical fiber. Alumina thin film is deposited onto the polished surface of a single-crystal organometallic perovskite optical fiber covered with a single-layer graphene film. A titanium dioxide thin film is coated or deposited onto the polished surface of a single-crystal organometallic perovskite optical fiber that is covered with a single-layer graphene film and an aluminum oxide film.

9. The method for fabricating an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 8, characterized in that, The preparation method of single-layer graphene film is one of the following: microcomputer exfoliation method, chemical vapor deposition method, and silicon carbide epitaxial growth method; The transfer method for single-layer graphene films is one of the following: direct growth method, polymethyl methacrylate film-assisted wet transfer method, or polydimethylsiloxane film-assisted dry transfer method.

10. The method for fabricating an electromagnetic field localization enhancement structure based on a double-layer film and side-polished perovskite optical fiber according to claim 8, characterized in that, The preparation methods for aluminum oxide thin films include one of the following: vacuum resistance heating evaporation, electron beam evaporation, magnetron sputtering deposition, pulsed laser deposition, chemical vapor deposition, plasma-enhanced chemical vapor deposition, atomic layer deposition, and sol-gel method. The titanium dioxide thin film is prepared by one of the following methods: vacuum resistance heating evaporation, electron beam evaporation, magnetron sputtering deposition, pulsed laser deposition, chemical vapor deposition, atomic layer deposition, or sol-gel method.

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