Hollow-core antiresonant fiber tunable filter

Abstract

The present invention discloses a hollow-core antiresonant fiber tunable filter, comprising an antiresonant fiber and a metasurface, wherein the metasurface is located on the end face of the antiresonant fiber; the antiresonant fiber comprises a quartz cladding, a glass wall, and an air core; the metasurface is a flexible substrate and a periodically arranged array of metal holes, periodically distributed in the x and y directions; light emitted by the antiresonant fiber is incident on the metasurface, whereupon plasma waves are generated on the metal surface, generating plasma resonance at specific wavelengths to achieve filtering; pressure is applied to the side of the antiresonant fiber to produce a certain deformation, thereby adjusting the period of the metasurface in the x and y directions and achieving dynamic modulation of the plasma coupled resonance. The present invention utilizes the metasurface to regulate the output light field of the antiresonant fiber, achieving efficient optical transmission and modulation in the mid-infrared band. By adjusting the applied pressure, the plasma coupled resonance can be dynamically adjusted to select different operating wavelengths.

Description

Technical Field

[0001] The present invention belongs to the field of optical technology, and in particular relates to an integrated hollow-core antiresonant optical fiber tunable filter based on a flexible substrate metasurface. Background Art

[0002] In recent years, a hollow-core antiresonant fiber has been proposed. It uses antiresonance to confine light in a large-diameter air-hole core for transmission. This can largely avoid the various problems caused by the intrinsic defects of the quartz material, greatly reducing the absorption loss of the quartz material in the mid-infrared band. This fiber has the advantages of a large core diameter, a wide transmission bandwidth, low loss, and a high laser damage threshold.

[0003] Hollow-core antiresonant fibers transmit light through large-diameter air holes. Unlike traditional solid-core fibers, they cannot directly modulate parameters such as the refractive index of the core material to create various optical modulation devices. Instead, they must be used in conjunction with independent components. Optical modulation devices based on hollow-core fibers suffer from issues such as bulkiness, high losses, and poor stability. With the development of artificial micro- and nanostructures, plasmon resonances generated on metal surfaces, formed by the periodic arrangement of subwavelength-sized structural units, modulate the amplitude, phase, and resonant wavelength of the incident wave, achieving functions such as filtering and focusing. By adjusting the structural size and periodic arrangement of the structural units, their plasmon-coupled resonances can be dynamically controlled. Using these artificial micro- and nanostructures, optical devices with compact size, high controllability, and stable performance can be fabricated.

[0004] Combining hollow-core antiresonant optical fibers with surface micro-nanostructure optical functional devices is expected to achieve efficient optical transmission and dynamic modulation. Summary of the Invention

[0005] To address the problem of antiresonant hollow-core fibers being unable to directly modulate the refractive index of their air cores to form intra-fiber modulation devices, the present invention provides an integrated hollow-core antiresonant fiber tunable filter based on a flexible substrate metasurface. This design aims to leverage the significant pressure-dependent characteristics of the hollow-core fiber's cross-section and the flexible substrate. By applying pressure to the fiber's sides, a metasurface in which array parameters are modulated by pressure can be created, enabling efficient transmission and dynamic modulation using antiresonant fibers.

[0006] The technical solutions adopted in the present invention are as follows:

[0007] An integrated hollow-core antiresonant fiber tunable filter based on a flexible substrate metasurface comprises an antiresonant fiber and a flexible metasurface, with the metasurface positioned on the end face of the antiresonant fiber. The antiresonant fiber comprises a quartz cladding, glass walls, and an air core, while the metasurface comprises a flexible substrate and a periodically arranged array of holes, distributed periodically in the x and y directions. Light emitted from the antiresonant fiber is incident on the metasurface, generating plasma waves on the metal surface and plasma resonance at specific wavelengths, thereby achieving filtering and other functions. Applying pressure to the side of the antiresonant fiber, causing a certain degree of deformation, allows the period of the metasurface in the x and y directions to be adjusted, achieving dynamic adjustment of the plasma-coupled resonance.

[0008] According to the above technical solution, the core diameter of the antiresonant hollow-core optical fiber is D, the inner diameter of the cladding tube is d, and the glass wall thickness is t; the optical fiber core diameter D is 25-35 μm, the inner diameter of the cladding tube d is 13-20 μm, and the glass wall thickness t is 0.6-1 μm.

[0009] Following the above technical solution, the metasurface substrate layer is made of flexible materials such as PDMS and PMMA.

[0010] Following the above technical solution, the material of the metasurface metal hole array is metal materials such as gold, silver, copper, and aluminum.

[0011] According to the above technical solution, the hole period P of the metasurface is 3-8 μm, the thickness h of the metasurface metal hole array is 0.4-1.2 μm, the side length L of the metasurface metal hole array is 2-4 μm, and the radius r of the metasurface metal hole is 0.8-1.2 μm.

[0012] When a beam of light is incident on the air core, it is approximately grazing incidence on the surface of the glass wall. Part of the light is emitted and returns to the core; the other part of the light is refracted and enters the glass wall, forming a Fabry-Perot-like resonant cavity in the glass wall. The light that meets the resonance conditions is leaked out, while the light that does not meet the resonance conditions returns to the core through anti-resonance and propagates, so the light can be confined to propagate in the air core.

[0013] When light transmitted by the air holes of the hollow-core antiresonant fiber is incident on the periodic metal hole structure of the metasurface, surface plasmon waves are generated on the upper surface of the metal hole array due to the diffraction wave vector compensation effect of the periodic hole structure. The light is then transmitted to the lower surface of the metal hole array through the coupling effect of the metal holes, thereby achieving effective enhancement of the transmitted electromagnetic wave at a specific wavelength.

[0014] By applying pressure to the side of the antiresonant fiber, the cross section of the antiresonant fiber and the flexible metasurface are deformed, and the period of the metasurface in the x and y directions is adjusted to achieve dynamic adjustment of the plasma coupled resonance.

[0015] During simulation calculations, the spatial distribution of the light field of the hollow-core antiresonant fiber is obtained through mode analysis. The three components of the electric field are defined as interpolation functions, and the three functions are set at the ports of the metasurface respectively, so that the metasurface can realize the regulation of the output light field of the antiresonant fiber.

[0016] This filter uses a metasurface to regulate the output light field of the antiresonant fiber, achieving efficient optical transmission and modulation in the mid-infrared band. By adjusting the applied pressure, the dynamic adjustable function of the plasma coupling resonance can be achieved, and different operating wavelengths can be selected.

[0017] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0018] The present invention uses a hollow-core antiresonant fiber as a transmission medium and a flexible metasurface as a modulation device, which can not only effectively transmit light in the mid-infrared band, but also use the flexibility of the substrate to achieve dynamic regulation to meet different filtering requirements. Pressure is applied to the side of the antiresonant fiber to produce a certain deformation, thereby adjusting the period of the metasurface in the x and y directions, realizing dynamic adjustment of plasma coupled resonance. This has broad application prospects for transmission, modulation and dynamic regulation using antiresonant hollow-core fibers in the mid-infrared band. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the structure of the hollow-core antiresonant fiber tunable filter according to an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the end face structure of a hollow-core antiresonant optical fiber according to an example of the present invention;

[0021] Figure 3 Schematic diagram of the flexible metasurface structure and unit structure diagram of an example of the present invention;

[0022] Figure 4 This is a transmission spectrum diagram of the hollow-core antiresonant fiber tunable filter according to an example of the present invention;

[0023] Figure 5 Schematic diagram of the pressure exerted on the flexible metasurface structure of an example of the present invention in a hollow-core antiresonant optical fiber;

[0024] Figure 6 Schematic diagram of the change in spacing of the metal hole array of the flexible metasurface structure under pressure according to an example of the present invention;

[0025] Figure 7 These are transmission spectra of the flexible metasurface filter of an example of the present invention under pressures of F1, F2, and F3 respectively.

[0026] In the figure: 1-quartz cladding, 2-glass wall, 3-air core, 4-metal hole film, 5-flexible substrate. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0028] The flexible metasurface filter of the present invention can transmit and regulate light in the mid-infrared band. By applying pressure to the optical fiber, a certain deformation can be generated, thereby adjusting the period of the metasurface in the x and y directions, changing the coupled resonance effect of the plasma, and thus causing the resonant wavelength to drift, thereby obtaining a flexible tunable filter in the mid-infrared band.

[0029] The integrated hollow-core antiresonant fiber tunable filter based on a flexible substrate metasurface according to an embodiment of the present invention comprises an antiresonant fiber and a flexible metasurface. The metasurface is located on the end face of the antiresonant fiber. The antiresonant fiber comprises a quartz cladding, a glass wall and an air core, the metasurface is a flexible substrate and a periodically arranged hole array, the substrate material is a flexible material such as PDMS, PMMA, and the hole-shaped metal film material is a metal material such as gold, silver, copper, and aluminum. Figure 2 and Figure 3 As shown, the required structural parameters are: the core diameter of the antiresonant hollow-core optical fiber is D, the inner diameter of the cladding tube is d, the thickness of the glass wall is t, the hole period of the metasurface is P, the thickness of the metasurface metal hole array is h, the side length of the metasurface metal hole array is L, and the radius of the metasurface metal hole is r; wherein the structural parameters are preferably optical fiber D = 25-35 μm, d = 13-20 μm, t = 0.6-1 μm, P = 3-8 μm, h = 0.4-1.2 μm, L = 2-4 μm, and r = 0.8-6 μm.

[0030] like Figure 1 and Figure 2 As shown, the integrated hollow-core antiresonant fiber tunable filter based on a flexible substrate metasurface of an example of the present invention includes an antiresonant fiber and a flexible metasurface, wherein the antiresonant fiber includes a quartz cladding 1, a glass wall 2, and an air core 3, and the metasurface structure includes a metal hole film 4 and a flexible substrate 5. Furthermore, the periodic metal hole film is processed to the size of the air core and placed into the air core hole at the end face of the hollow-core antiresonant fiber. By bonding the substrate and the quartz cladding, the metasurface is processed to the end face of the antiresonant fiber, thereby enabling the metasurface to control the output light field of the antiresonant fiber.

[0031] In the present invention, the light guiding mechanism of the hollow core antiresonant optical fiber is based on the antiresonant reflecting optical waveguide (ARROW) model, which is a planar waveguide theory. The principle of antiresonant light guiding is similar to that when a beam of light is incident on the air core, it is approximately grazing incidence on the surface of the glass wall. Part of the light is emitted and returns to the core; the other part of the light is refracted and enters the glass wall, forming a Fabry-Perot-like resonant cavity in the glass wall. The wavelength of the incident light and the thickness of the glass wall determine the resonance condition and antiresonance condition of the resonant cavity. The light that meets the resonance condition is leaked out, and the light that does not meet the resonance condition returns to the core through the antiresonance effect and propagates. Through this principle, the light can be confined to propagate in the air core. From Snell's law and the principle of the Fabry-Perot cavity, the antiresonance condition can be deduced as follows:

[0032]

[0033] Where λ is the incident wavelength, t is the glass wall thickness, n1 is the glass wall refractive index, n0 is the air refractive index, and m is the resonance order. When the antiresonance condition is met, the glass wall reflects the maximum amount of light and transmits the minimum amount of light. Most of the light is reflected back into the fiber core, thereby transmitting light through the air holes.

[0034] In the present invention, when light transmitted through the air holes of a hollow-core antiresonant fiber is incident on the periodic metal hole structure of the metasurface, surface plasmon waves are generated on the upper surface of the metal hole array due to the diffraction wave vector compensation effect of the periodic hole structure. These waves are then transmitted to the lower surface of the metal hole array through coupling with the metal holes, thereby effectively enhancing the transmitted electromagnetic wave at a specific wavelength. The surface plasmon wavelength is calculated as follows:

[0035]

[0036] Among them, λ spp is the wavelength of the surface plasmon wave, P is the period of the metal hole, i and j are the orders of the electromagnetic wave mode, ε1 and ε2 are the dielectric constants of the metal hole array and the substrate, respectively.

[0037] In the present invention, the thickness of the metal hole array and the radius of the metal holes have a direct impact on the Fabry-Perot resonant cavity, that is, they affect the coupling of the surface plasmon wave, and thus affect the electromagnetic wave transmittance. Therefore, the thickness of the metal hole array and the radius of the metal holes can be adjusted. In different situations, by selecting appropriate parameters, the filter can achieve the desired effect.

[0038] The hole period P of the metasurface structure directly affects the resonant wavelength of the plasma wave, such as Figure 5 and Figure 6 As shown, applying pressure on the side of the optical fiber will cause the flexible substrate to deform in the x and y directions, resulting in a change in the spacing of the metal hole array, thereby changing the period P x and P y Changes have occurred. Figure 4 and 7 As shown in Figure 2, the wavelength of the electromagnetic wave transmitted by the metasurface is enhanced at different times under different hole periods. Therefore, the position of the resonant wavelength can be adjusted by adjusting the pressure. This has a wide range of applications in the mid-infrared band.

[0039] In summary, the present invention combines antiresonant fiber as a transmission medium and a flexible metasurface as a modulation device, effectively transmitting light in the mid-infrared band. Furthermore, the substrate's flexibility allows for dynamic regulation to meet diverse filtering requirements. This holds great promise for the use of antiresonant hollow-core fiber for transmission, modulation, and dynamic adjustment in the mid-infrared band.

[0040] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, or two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0041] It will be easily understood by those skilled in the art that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A hollow-core antiresonant fiber tunable filter, characterized in that: The invention comprises an antiresonant optical fiber and a metasurface, wherein the metasurface is located on the end face of the antiresonant optical fiber; wherein the antiresonant optical fiber comprises a quartz cladding, a glass wall and an air core; and the metasurface is a flexible substrate and a periodically arranged metal hole array, which is periodically distributed in the x and y directions; the hole period P of the metasurface is 3-8 μm, the thickness h of the metal hole array of the metasurface is 0.4-1.2 μm, the side length L of the metal hole array of the metasurface is 2-4 μm, and the radius r of the metal hole of the metasurface is 0.8-1.2 μm; When light emitted from the antiresonant fiber is incident on the metasurface, plasma waves are generated on the metal surface, which then produces plasma resonance at a specific wavelength to achieve filtering. Applying pressure to the side of the antiresonant fiber creates a certain deformation, which adjusts the periodicity of the metal hole arrays arranged periodically on the metasurface in the x and y directions, thus achieving dynamic modulation of the plasma coupling resonance. The calculation formula of the surface plasmon wavelength is: in, is the wavelength of the surface plasmon wave, is the period of the metal hole, and is the electromagnetic wave mode order, and are the dielectric constants of the metal hole array and the substrate, respectively.

2. The hollow-core antiresonant fiber tunable filter according to claim 1, wherein: The conditions for anti-resonance are: in, is the incident wavelength, is the glass wall thickness, is the refractive index of the glass wall, is the refractive index of air, is the resonance order.

3. The hollow-core antiresonant fiber tunable filter according to claim 1, wherein: A periodic metal hole film is processed into the size of an air core and placed into the air core hole at the end face of a hollow-core antiresonant optical fiber. The metasurface is processed onto the end face of the antiresonant optical fiber through bonding between the substrate and the quartz cladding.

4. The hollow-core antiresonant fiber tunable filter according to any one of claims 1 to 3, wherein: The air core diameter D is 25-35 μm, the inner diameter d of the quartz cladding tube is 13-20 μm, and the glass wall thickness t is 0.6-1 μm.

5. The hollow-core antiresonant fiber tunable filter according to any one of claims 1 to 3, wherein: The metasurface substrate material is a flexible material, including PDMS or PMMA.

6. The hollow-core antiresonant fiber tunable filter according to any one of claims 1 to 3, wherein: The material of the metasurface metal hole array is metal material, including gold, silver, copper or aluminum.

Images