An all-fiber circular Airy beam generator

Abstract

The application provides a full-optical fiber circular Airy light generating device, which is characterized by being composed of a single-mode optical fiber (1), a multi-mode optical fiber (2), a metal film (3) and a circular groove plasmonic antenna array (4). The multi-mode optical fiber (2) is fused on the single-mode optical fiber (1) and plays a role of expanding the transmission light field in the single-mode optical fiber core. The metal film (3) is plated on the end face of the multi-mode optical fiber (2). The circular groove plasmonic antenna array (4) is etched on the metal film (3). The transmission light field expanded by the multi-mode optical fiber (2) is irradiated on the circular groove plasmonic antenna array (4) to excite a plasmonic wave, and the plasmonic wave is then radiated and output through the circular groove plasmonic antenna array (4) to form a fiber end output light field. The groove size parameters, groove quantity and arrangement mode of the circular groove plasmonic antenna array (4) are designed according to the fiber end output light field being circular Airy light. The application belongs to the technical field of fiber microstructure devices.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber microstructure device technology. In particular, it relates to generating circular Airy light by designing and fabricating a plasma antenna on the end face of an optical fiber. Background Technology

[0002] Circular Airy beams, due to their unique self-focusing, self-accelerating, and self-healing properties, have significant applications in fields such as microscopic imaging, particle manipulation, and high-intensity light packet generation, attracting widespread attention. For these important applications, the efficient generation and flexible control of circular Airy beams are crucial. Generating circular Airy beams using spatial light modulators is a traditional method, offering flexibility, but the large size of these modulators makes integration impossible. In recent years, many on-chip integrated circular Airy beam generators have been proposed using on-chip integrated photonic devices such as metasurfaces and surface plasmon antennas. While these on-chip integrated circular Airy beam generators meet the growing demand for highly integrated devices, they also have inherent limitations in certain specific applications. For example, when using circular Airy beams for particle manipulation, especially for manipulating cells and drug particles in biological tissue solutions, the on-chip integrated circular Airy beam generator must be placed in the tissue solution. This poses a significant challenge to optical path alignment, and the various scattering effects of the tissue solution on the incident light significantly affect the quality of the generated circular Airy beam, making it highly unsuitable for practical applications.

[0003] Optical fiber is another important optical field manipulation platform, distinct from traditional optical components and on-chip integrated optical platforms. On the one hand, fiber optic devices are small in size and easy to integrate, such as into microfluidic chips; on the other hand, fiber optics confine the optical field within the fiber core, thus enabling easy remote control and strong anti-interference capabilities. They can be inserted into thick samples and turbid media, greatly improving their adaptability to various application scenarios. Furthermore, fiber optic devices are flexible, providing high application flexibility. Due to these unique advantages, developing fiber-optic circular Airy beam generators can effectively avoid the shortcomings of on-chip integrated circular Airy beam generators in practical applications. Therefore, developing all-fiber circular Airy beam generators is of great significance. To this end, the paper [Optics Letters, 41.4, (2016): 824-827] designs a ring array waveguide fiber to generate circular Airy beams. However, the ring array waveguide fiber they designed is a special fiber that needs to be drawn in batches individually, resulting in high costs. In addition, once this fiber is drawn, it is fixed to a specific parameter. If circular Airy light with other parameters is to be generated, a new ring array waveguide fiber needs to be designed and drawn. This is very disadvantageous for practical applications.

[0004] In addition, inventors Li Hehe et al. disclosed in 2019 and Shou Qian et al. in 2020 a method for flexibly adjusting the self-focusing focal length of a self-focusing beam (Chinese Patent: CN201911368077.3) and a device and method for moving the self-focusing point of a circular Airy beam over a large range with high precision (Chinese Patent: CN202010091010.6), respectively. These inventions mainly utilize computer holography and spatial light modulators to load different phase diagrams to achieve the purpose of changing the position of the beam's self-focusing point; inventors Wei Bingyan et al. in 2020... A liquid crystal beam splitter, preparation method and generation system for a circular Airy beam disclosed in 2010 (Chinese Patent: CN202010669528.3) mainly utilizes polarization to generate a self-focusing and defocusing circular Airy beam and achieves spatial separation; an optical geometric phase element design method and self-focusing lens device for generating a circular Airy beam by complex amplitude modulation disclosed by inventors Zhu Zhihan et al. in 2022 (Chinese Patent: CN202211366505.0) uses a geometric phase element to realize the self-focusing characteristics of the Airy beam and simplifies the optical path.

[0005] However, the structures that generate circular Airy beams generally suffer from the disadvantages of large optical path volume and inability to be integrated. For example, the device for moving the self-focusing point of a circular Airy beam over a large range and with high precision disclosed by Shou Qian et al. (Chinese Patent: CN202010091010.6) requires a large lens group and spatial light modulator and other devices in the optical path.

[0006] Against this backdrop, it is of great significance to develop a low-cost, efficient, simple, easy-to-integrate, and flexibly designable all-fiber circular Airy light generation device, which can make up for the shortcomings of existing circular Airy light generation methods in practical applications. Summary of the Invention

[0007] This invention provides an all-fiber circular Airy light generating device.

[0008] The all-fiber circular Airy light generating device provided by this invention is implemented as follows:

[0009] The all-fiber circular Airy light generating device comprises a single-mode fiber 1, a multimode fiber 2, a metal thin film 3, and a ring-groove plasma antenna array 4. The multimode fiber 2 is fused to the single-mode fiber 1, serving to expand the transmitted light field in the core of the single-mode fiber 1. The metal thin film 3 is deposited on the end face of the multimode fiber 2. The ring-groove plasma antenna array 4 is etched onto the metal thin film 3. The transmitted light field, expanded by the multimode fiber 2, irradiates the ring-groove plasma antenna array 4, exciting a plasma wave. This plasma wave is then radiated out through the ring-groove plasma antenna array 4, forming the output light field at the fiber end. The groove size parameters, number of grooves, and arrangement of the ring-groove plasma antenna array 4 are designed based on the principle that the output light field at the fiber end is circular Airy light, ensuring that the generated light field is circular Airy light. By designing ring-groove plasma antenna arrays with different parameters, circular Airy light with different parameters can be generated.

[0010] The specific design principle of the annular groove plasma antenna array is as follows: Figure 3 The following explanation is provided. The width W of the annular slit in the annular groove plasma antenna array is described. The etching depth of the annular slit in the annular groove plasma antenna array is H, while the etching depth of the other annular grooves is less than H. This means that only the gold film at the annular slit is etched through, ensuring that when the light field transmitted in the optical fiber irradiates the annular groove plasma antenna array, surface plasmon polaritons (SPPs) are excited only at the annular slit. The excited SPPs are... Figure 3 The light field, indicated by the middle arrow, propagates along the surface of the gold film and is decoupled into free space by the annular grooved plasma antenna array during propagation. Let θ be the angle between the propagation direction of the decoupled free space light field and the z-axis, and let N be the number of annular grooves. n It is the distance between the nth annular groove and the center of the optical fiber. The distance between the (n-1)th and nth annular grooves from the inside out is b. n =r n -r n-1 The phase difference between the light fields decoupled from adjacent annular grooves to free space follows the following relationship:

[0011] k0b n sin θ=k spp b n +2π (1)

[0012] k0 is the free space wave vector 2π / λ. It is the wave vector of SPPs on the gold film surface, ε d and ε gIt is the relative permittivity of air and gold film. It establishes the relationship between the phase change of the light field decoupled from adjacent annular grooves to free space and the distance between adjacent annular grooves when the diffraction angle is the same. From formula (1), it can be seen that when the diffraction angle is the same, the phase change of the light field decoupled from adjacent annular grooves to free space is related not only to the distance between the annular grooves, but also to an additional phase difference of 2π. Then the phase evolution of the light field decoupled from the nth annular groove to free space can be derived as follows:

[0013] φ n (r n )=φ0+k spp (r n -r0)+2nπ (2)

[0014] Where φ0 is the initial phase at the annular slit, and r0 is the distance from the annular slit to the center of the fiber, we obtain the relationship between the phase of the optical field decoupled from the annular groove to free space and the position of the annular groove.

[0015] To achieve a circular Airy beam output, the expression for the optical field at the fiber end face, i.e., the z=0 plane, needs to be designed to resemble that of a finite-energy circular Airy beam, namely:

[0016]

[0017] 'a' is the exponential cutoff factor, x0 determines the transverse acceleration of the Airy beam and is related to the beam focusing position. The phase distribution of a circular Airy beam is related to the sine term as follows:

[0018]

[0019] If we approximate the phase distribution of the light field decoupled from the annular groove array to free space as the phase distribution of a circular Airy light, and set the initial phase φ0 = 0, then the position r of the nth annular groove on the gold film surface is... n This can be obtained by solving the equation:

[0020]

[0021] By solving Equation 5, the position of the annular groove array is designed, and the resulting annular groove array decouples the optical field phase distribution in free space to have the phase distribution of a circular Airy beam. Simultaneously, the circular Airy beam has finite energy, and its amplitude gradually weakens as it propagates outwards, satisfying (r). -1 / 4 The amplitude distribution of the optical field is approximately satisfied by the SPP field strength attenuated in the propagation of the annular groove array, so that the output optical field of the fiber end face has the phase and amplitude distribution of the circular Airy optical field, thus obtaining a circular Airy beam.

[0022] In this invention, the thickness H of the metal film on the fiber end face is ≥100nm, and the number of annular grooves in the annular groove plasma antenna array is N≥5, which can be adjusted according to the specific requirements of the required fiber end face size. The depth and width of the annular slits in the annular groove plasma antenna array significantly affect the excitation efficiency of the plasma field. For a specific excitation wavelength (taking 980nm as an example), the maximum excitation efficiency can be obtained by optimizing these parameters. Taking the optimization of the annular slit parameters as an example, we used FDTD software to establish a simulation model of the annular slit. By continuously optimizing the parameters of the annular slit, we finally found that when the annular slit width W is about 130nm and the annular slit depth H is about 200nm, the incident light with a wavelength of 980nm has the highest plasma excitation efficiency.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention proposes an all-fiber circular Airy light generating device, which has all the advantages of fiber optic photonic devices.

[0025] 2. The all-fiber circular Airy light generating device proposed in this invention uses ordinary commercial single-mode fiber and multi-mode fiber, without the need to separately draw special fiber, thus effectively controlling costs.

[0026] 3. The all-fiber circular Airy light generating device proposed in this invention can generate circular Airy light with different parameters by designing annular groove plasma antenna arrays with different parameters, which has extremely high design flexibility. At the same time, the annular groove plasma antenna array can be mass-produced by micro-nano fabrication technology, which is beneficial to meet diverse practical applications. Attached Figure Description

[0027] 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.

[0028] Figure 1 This is a schematic diagram of the structure of the all-fiber circular Airy light generating device provided in an embodiment of the present invention.

[0029] Figure 2 This is a simulation diagram of the XZ plane light field intensity distribution inside a fiber when a 980nm wavelength beam is coupled from a single-mode fiber to a graded-index multimode fiber, as provided in an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of the XZ cross section of slit-excited surface plasma waves (SPPs) provided in an embodiment of the present invention.

[0031] Figure 4 The distance r between the center position of the annular groove and the central axis of the optical fiber when x0 = 0.1µm, as provided in this embodiment of the invention, is... n A schematic diagram.

[0032] Figure 5 These are FDTD simulation results of the light intensity distribution of the output circular Airy light from the all-fiber circular Airy light generator provided in this embodiment of the invention. Figure 5 (A) is the optical field intensity distribution diagram of the XZ plane. a1, a2, a3, a4, a5, a6, a7, a8, and a9 are the optical field intensity distribution diagrams in the XY plane at distances of 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm, 24 μm, and 27 μm from the fiber end face, respectively.

[0033] Figure 6 The light intensity distribution of the circular Airy light output by the all-fiber circular Airy light generating device provided in this embodiment of the invention is the FDTD simulation result when designing annular groove plasma antenna arrays with different parameters. Detailed Implementation

[0034] 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.

[0035] A schematic diagram of the all-fiber circular Airy light generator proposed in this invention is shown below. Figure 1 The system comprises a single-mode fiber 1, a multimode fiber 2, a metal thin film 3, and a ring-groove plasma antenna array 4. In this embodiment, a commercially available 980nm single-mode fiber is selected as the single-mode fiber, a graded-index multimode fiber is selected as the multimode fiber, and a 200nm thick gold film is selected as the metal thin film. The simulation results of the XZ plane optical field intensity distribution inside the fiber when a 980nm wavelength beam is coupled from the single-mode fiber to the graded-index multimode fiber are as follows: Figure 2 As shown, splicing a 250µm long graded-index fiber onto a single-mode fiber can maximize beam expansion. The function of the annular groove plasma antenna array is to excite surface plasmon waves (SPPs) when irradiated by the light field after beam expansion by the multimode fiber. Subsequently, the SPPs are decoupled into free space by the annular groove plasma antenna array, generating an output light field, such as... Figure 3 As shown. By rigorously designing the annular groove plasma antenna array structure, the output light field can be made to be circular Airy light. In this embodiment,

[0036] In this embodiment, circularly polarized light with a wavelength of λ = 980 nm and a 250 μm long multimode fiber are selected. An annular slit with a radius of r0 = 3.5 μm, a depth of 200 nm, and a width of 130 nm is etched onto a 200 nm thick gold film. Eight annular grooves, each with a depth of 75 nm and a width of 260 nm, are concentric with the annular slits. The positions of each annular groove are calculated according to formula (5), resulting in structures with distances from the annular grooves to the annular slits of 4.268 μm, 5.08 μm, 5.87 μm, 6.64 μm, 7.38 μm, 8.11 μm, 8.83 μm, and 9.53 μm, respectively. Figure 4 The figure shows the distance r between the center of the annular groove and the central axis of the optical fiber. n The schematic diagram shows the light field intensity distribution in the XZ plane above the end face. The results are as follows: Figure 5 Figure (A) shows the optical field intensity distribution in the XZ plane. a1, a2, a3, a4, a5, a6, a7, a8, and a9 represent the XY plane optical field intensity distributions at locations of 3 μm, 6 μm, 9 μm, 12 μm, 15 μm, 18 μm, 21 μm, 24 μm, and 27 μm above the fiber end face, respectively. By changing the value of x0, the circular Airy beam can be focused at different positions, such as... Figure 6 As shown, Figure 6 (A) is the XZ plane light intensity distribution map obtained when x0 = 1um, and (B) is the XZ plane light intensity distribution map obtained when x0 = 1.25um.

[0037] 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 circular Airy light generating device, comprising a single-mode fiber (1), a multimode fiber (2), and a metal thin film (3), characterized in that, It also includes an annular groove plasma antenna array (4) etched on the metal thin film (3); the multimode fiber (2) is fused to the single-mode fiber (1) to expand the transmission optical field in the core of the single-mode fiber (1); the metal thin film (3) is deposited on the end face of the multimode fiber (2); the annular groove plasma antenna array (4) is etched on the metal thin film (3); the transmission optical field expanded by the multimode fiber (2) can excite plasma waves when it shines on the annular groove plasma antenna array (4), and the plasma waves are then radiated out through the annular groove plasma antenna array (4) to form the output optical field at the fiber end; the position of the concentric annular groove in the annular groove plasma antenna array (4) is designed according to the desired fiber end phase distribution of the non-diffraction circular Airy light, and the position r of the concentric annular groove is determined by solving the following formula. n : Where φ0 is the initial phase, k spp is the wave vector of SPPs on the gold film surface, r0 is the distance from the annular slit to the center of the optical fiber, n represents the nth concentric annular groove, and x0 is a parameter in the phase of the circular Airy light. The width and depth of the concentric annular groove are designed according to the desired fiber-end amplitude distribution of the non-diffractive circular Airy light, so that the generated optical fiber-end output light field is circular Airy light.

2. The all-fiber circular Airy light generating device according to claim 1, characterized in that: The number of concentric annular grooves in the annular groove plasma antenna array (4) is N, and N≥5 can be adjusted according to the specific requirements of the required fiber end face size.

3. The all-fiber circular Airy light generating device according to claim 1, characterized in that: The metal thin film (3) may be gold or silver or a material capable of exciting surface plasma waves, and its thickness is H, where H ≥ 100 nanometers.

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