All-fiber sub-wavelength vector light field generating device

Abstract

The invention provides an all-fiber sub-wavelength vector light field generating device. The device is characterized by comprising a single-mode optical fiber (1), a coreless optical fiber (2) and a double-ring plasma structure (3). The coreless optical fiber (2) is welded on the single-mode optical fiber (1) and plays a role in expanding a transmission light field in a fiber core of the single-mode optical fiber (1). The double-annular plasma structure (3) is arranged on the end face of the coreless optical fiber (2) and is composed of rectangular nanometer slits with the same size. When circularly polarized light with a specific wavelength is coupled and incident into the device, the circularly polarized light is expanded by the coreless optical fiber (2) and then is irradiated on the double-ring plasma structure (3), and a sub-wavelength vector light field can be generated on the end face of the optical fiber. The invention belongs to the technical field of optical fiber microstructure devices.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber microstructure device technology, specifically involving the generation of a subwavelength vector light field by designing and fabricating a double-ring plasma structure on the end face of an optical fiber and coupling in circularly polarized light of a specific wavelength. Background Technology

[0002] Vector beams are a type of structured light whose polarization state varies with spatial position within a transverse cross-section. Typical examples include radially polarized beams and azimuthally polarized beams. Due to their key property of "polarization state spatial structure," which distinguishes them from uniformly polarized light, these beams exhibit unique advantages in focusing, imaging, micro / nano fabrication, and light-matter interactions. For example, under high numerical aperture focusing conditions, radially polarized beams can generate a significant longitudinal electric field component in the focal region, resulting in a sharper, axially concentrated focal spot and stronger local field distribution characteristics, thus driving the development of applications such as high-resolution microscopy and particle manipulation. Existing technologies have developed various approaches to the generation and manipulation of vector beams, including combinations of traditional polarization optical devices, spatial light modulation / interference superposition, and the rapidly developing planar metasurface schemes. However, the overall approach remains focused on "spatial manipulation of transverse (cross-section) polarization states," primarily aiming to design and convert the spatial distribution of polarization within the transverse plane.

[0003] On the other hand, besides the lateral dimension, the propagation direction (longitudinal) is also an important degree of freedom for optical field manipulation. In recent years, vector beams with "controllable evolution of polarization state with propagation distance" (also known as longitudinally variable polarization vector beams, propagation-modulated vector beams, etc.) have further expanded the dimensions of vector beam manipulation, allowing the beam to exhibit different polarization states / polarization structures at different longitudinal positions, providing new possibilities for three-dimensional scenarios such as bulk fabrication, longitudinal detection, and micro-manipulation of living organisms. Existing research shows that such beams typically rely on the coherent superposition of different eigenmodes / different polarizations or different phase components, and utilize the phase accumulation difference during free-space propagation to achieve the longitudinal evolution of the polarization structure; there are also schemes using metasurfaces and other micro / nano devices to achieve propagation modulation. However, the above schemes often require complex free-space optical paths in engineering implementation (such as multi-device cascading, precise alignment, stable interference, or strict incident conditions), and the system size and environmental sensitivity limit their application in compact integration, long-distance delivery, and complex media environments.

[0004] Optical fiber, as an important light field manipulation and transmission carrier distinct from traditional free-space optics and on-chip integrated optical platforms, possesses characteristics such as small size, easy integration, flexibility, remote delivery, and strong anti-interference ability, making it particularly suitable for introducing structured light into thick samples, turbid media, or confined spaces. However, after traditional optical fibers are drawn into shape, their optical characteristics, such as the propagation direction of guided modes, mode distribution, and polarization state, are usually difficult to flexibly reconstruct at the "fiber-end output end," resulting in the generation of structured light (including vector beams) still relying more on "bulk optical systems outside the fiber" for a considerable period of time. To overcome these bottlenecks, in recent years, optical fiber-integrated metasurfaces and "metafiber" platforms, which integrate metasurfaces / nanostructures at the fiber end face, have been proposed and developed. These platforms can perform subwavelength-scale shaping of the phase, amplitude, and polarization of outgoing light at the fiber end, and even achieve arbitrary structured light transformations on mixed-order Poincaré spheres. At the same time, reports have emerged of fiber end-face devices that utilize plasmon resonance / metasurface mechanisms to achieve polarization or mode conversion. Nevertheless, achieving the simultaneous realization of "subwavelength-scale vector optical field" and "longitudinal polarization state change" still generally faces problems such as complex device structure and fabrication process, limited efficiency / bandwidth and polarization robustness, and difficulty in matching with fiber system-level packaging. Therefore, there is an urgent need for a device solution that can achieve compact integration in an all-fiber system and output a subwavelength vector optical field with longitudinal polarization evolution characteristics. Summary of the Invention

[0005] This invention provides an all-fiber subwavelength vector light field generating device.

[0006] The all-fiber subwavelength vector optical field generating device provided by this invention is implemented as follows:

[0007] The all-fiber subwavelength vector light field generating device, such as Figure 1 As shown, the device consists of a single-mode fiber 1, a coreless fiber 2, and a double-ring plasma structure 3. The coreless fiber 2 is fused to the single-mode fiber 1 and serves to expand the optical field transmitted in the core of the single-mode fiber 1. The double-ring plasma structure 3 is located at the end face of the coreless fiber 2 and is composed of rectangular nano-slits of the same size. When circularly polarized light of a specific wavelength is coupled into the device, it is expanded by the coreless fiber 2 and then irradiates the double-ring plasma structure 3, which can generate a subwavelength vector light field at the end face of the fiber.

[0008] The specific design principle of the double-ring plasma structure 3 is as follows: Figure 2 As shown, by using FDTD scanning of rectangular nanoslits of different sizes, circularly polarized light incident on a rectangular nanoslit of a specific size is transformed into linearly polarized light perpendicular to the long axis of the rectangular nanoslit. Figure 2As shown in (a, b), a double-ring plasma structure 3 was constructed using the obtained rectangular nanoslits, as follows. Figure 2 As shown in (c), by setting rectangular nanoslits parallel to the x-axis and parallel to the y-axis at distances r1 and r2 from the fiber core, respectively, the linearly polarized light in the x-direction (purple line) and the linearly polarized light in the y-direction (brown line) generated by the mutually perpendicular slits at different positions on the fiber end face propagates along different paths to the z-axis. Therefore, based on geometric relationships, it can be easily derived that the optical paths of the linearly polarized light in the x-direction and the linearly polarized light in the y-direction propagating to a point on the z-axis are respectively... and The phase difference between the two linearly polarized lights is:

[0009] (1)

[0010] in, λ is the wavelength of the incident light. The phases of the linearly polarized light propagating along the z-axis in the x and y directions are respectively... and The Jones matrix of the radial vector light field generated by the superposition of linearly polarized light in the x-direction and y-direction along the z-axis is:

[0011] (2)

[0012] Where A x and A y These represent the amplitudes of the linearly polarized light transmitted along the z-axis in the x and y directions, respectively. As the z-value changes, the polarization state of the generated vector beam changes with the distance the light field propagates.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] 1. The present invention proposes an all-fiber subwavelength vector light field generating device, which has all the advantages of fiber photonic devices.

[0015] 2. The all-fiber subwavelength vector optical field generating device proposed in this invention uses ordinary commercial single-mode optical fiber and coreless optical fiber, without the need to separately draw special optical fiber, thus effectively controlling costs.

[0016] 3. The all-fiber subwavelength vector optical field generating device proposed in this invention can generate the required fiber-end vector optical field by designing a double-ring plasma structure, which has extremely high design flexibility and is conducive to meeting diverse application needs. Attached Figure Description

[0017] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of an all-fiber subwavelength vector light field generating device provided in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram and design principle illustration of the rectangular nanoslit structure constituting the double-ring plasma structure provided in the embodiments of the present invention. (a) Circularly polarized light incident on a slit parallel to the y-axis generates linearly polarized light in the x-direction. (b) Circularly polarized light incident on a slit parallel to the x-axis generates linearly polarized light in the y-direction. (c) Optical path diagram at the fiber end.

[0020] Figure 3 This is a distribution diagram of the intensity of the light field emitted from the fiber end provided in an embodiment of the present invention. (a) shows the intensity distribution of the light field emitted from the fiber end in the XZ plane. (b)-(g) show the normalized intensity distribution of the light field along the x-axis and the intensity distribution of the light field in the XY plane, respectively, when the light field emitted from the fiber end is at Z=8μm, 12μm, 16μm, 20μm, 24μm, and 28μm above the fiber end at y=0μm, and the polarization ellipse of the light field superimposed on the intensity distribution diagram. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other instances obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] A schematic diagram of the all-fiber subwavelength vector optical field generating device proposed in this invention is shown below. Figure 1 It consists of a single-mode fiber 1, a coreless fiber 2, and a double-ring plasma structure 3. In this embodiment, commercially available single-mode fiber and commercially available coreless fiber are selected, and the double-ring plasma structure is constructed through rectangular nanoslits of the same size.

[0023] In this embodiment, the thickness of the gold film is designed to be H=200nm, targeting the wavelength. Using FDTD scanning with circularly polarized light at 632 nm, the length of the rectangular nanoslits was determined to be L = 260 nm, the width W = 85 nm, the inner ring radius r1 = 13 μm, and the outer ring radius r2 = 14 μm. 180 rectangular nanoslits were evenly spaced at the inner ring positions with their long axes parallel to the horizontal direction, and 180 rectangular nanoslits were evenly spaced at the outer ring positions with their long axes perpendicular to the horizontal direction, thus constructing the desired double-ring plasma structure. (Wavelength...) When circularly polarized light of 632nm is coupled into an all-fiber device, the output light field at the fiber end is simulated using FDTD as follows: Figure 3 As shown. Figure 3 (a) shows the intensity distribution of the output light field at the fiber end in the XZ plane. Figure 3 Figures (b)-(g) show the normalized light intensity distribution along the x-axis and the light field intensity distribution in the XY plane, as well as the light field polarization ellipse superimposed on the light field intensity distribution, at Z = 8 μm, 12 μm, 16 μm, 20 μm, 24 μm, and 28 μm above the fiber end, respectively. According to the light field polarization ellipse, the polarization state of the light field at different positions above the fiber end changes continuously with the propagation of the light field. Furthermore, in the region Z < 30 μm from the fiber end face, the half-width at half-maximum (FWHM) of the light field is smaller than the incident light wavelength, exhibiting a subwavelength dimension, thus verifying that the generated light field is a subwavelength vector light field.

[0024] The above description discloses only one preferred embodiment of the present invention, and should not be construed as limiting the scope of the present invention. Those skilled in the art will understand that all or part of the processes of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. An all-fiber subwavelength vector optical field generating device, characterized in that: It consists of a single-mode fiber (1), a coreless fiber (2), and a double-ring plasma structure (3); the coreless fiber (2) is fused to the single-mode fiber (1) and serves to expand the transmitted light field in the core of the single-mode fiber (1); the double-ring plasma structure (3) is located on the end face of the coreless fiber (2) and is composed of rectangular nano-slits of the same size; when circularly polarized light of a specific wavelength is coupled into the device, it is expanded by the coreless fiber (2) and then irradiated onto the double-ring plasma structure (3), which can generate a subwavelength vector light field on the end face of the fiber.

2. The all-fiber subwavelength vector optical field generating device according to claim 1, characterized in that: The double-ring plasma structure (3) is composed of rectangular nanoslits of the same size, and the length and width of the rectangular nanoslits are optimized according to a specific wavelength.

3. The all-fiber subwavelength vector optical field generating device according to claim 1, characterized in that: The double-ring plasma structure (3) is composed of rectangular nanoslits of the same size, and the long axis of the nanoslits in the inner ring and the long axis of the nanoslits in the outer ring are perpendicular to each other.

4. The all-fiber subwavelength vector optical field generating device according to claim 1, characterized in that: The double-ring plasma structure (3) can be made of materials such as gold or silver that can excite surface plasma waves.

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