A method for preparing a superstructure surface at an end face of an optical fiber core

Abstract

The application discloses a method for preparing a superstructure surface on a fiber core end face, and relates to the technical field of micro-nano photonics. The method for preparing the superstructure surface on the fiber core end face comprises the following steps: S1. coating photoresist on the surface of a copper sacrificial layer, depositing TiO2 after forming a superstructure surface pattern groove through exposure, and then removing TiO2 on the surface of the photoresist to obtain a TiO2 superstructure surface; S2. making the TiO2 superstructure surface obtained in step S1 and a fiber core end face adhere to each other through ultraviolet curing glue to form an integrated structure, wherein the TiO2 superstructure surface completely covers the end face of the fiber core; and S3. soaking the integrated structure obtained in step S2 in a FeCl3 solution to remove the copper sacrificial layer, so that the superstructure surface on the fiber core end face is prepared. The method can realize lossless integration of the TiO2 superstructure surface on the fiber core end face and exclude an additional optical path caused by a substrate.

Description

Technical Field

[0001] This invention relates to the field of micro-nano photonics technology, and more specifically, to a method for fabricating metasurfaces on the end face of an optical fiber core. Background Technology

[0002] Optical fiber, with its excellent light guiding effect, large transmission capacity, low loss, and advantages such as high temperature resistance, corrosion resistance, and electromagnetic interference resistance, has become the core carrier of global optical communication networks and is widely used in various industries. In recent years, with the continuous advancement of informatization, optical fiber communication technology has continued to iterate and evolve. At present, optical fiber communication can achieve high-capacity, ultra-high-speed signal transmission; however, against the backdrop of the rapid development of emerging industries such as big data, cloud computing, industrial internet, Internet of Things, and artificial intelligence, data traffic is increasing dramatically, which also puts forward higher standards and new requirements for the miniaturization, integration, and intelligent development of optical fiber communication systems.

[0003] Metasurfaces are artificially designed two-dimensional electromagnetic materials that can flexibly manipulate the amplitude, phase, and polarization of incident light waves through specifically arranged subwavelength structural units on their surface, thus allowing for the shaping of the wavefront as needed. Integrating emerging metasurfaces with mature fiber optic platforms can break down the separation between electromagnetic signal transmission and modulation, enabling efficient signal manipulation. However, in the current microelectronics industry, most metasurfaces are fabricated on large planar substrates. Such manufacturing platforms are incompatible with fiber core end faces (especially single-mode fiber core end faces), which typically have diameters in the micrometer range. This limits the direct application of traditional nanofabrication techniques to fiber core end faces, posing a unique challenge to the fabrication of metasurfaces for fiber core end faces.

[0004] With advancements in manufacturing technology, researchers have developed numerous processes for integrating metasurfaces on fiber core end faces, such as two-photon laser printing, self-assembly, focused ion beam (FIB), and electron beam lithography (EBL). However, these processes have low compatibility with dielectric metasurfaces (i.e., metasurfaces constructed using inorganic high-refractive-index materials such as silicon nitride, TiO2, and hafnium oxide). Therefore, the current field primarily employs adhesive bonding technology to construct dielectric metasurfaces on fiber core end faces; that is, the adhesive-coated fiber core end face is precisely positioned and pressed onto the metasurface. However, currently, all processes utilizing adhesive bonding to integrate fiber end faces and metasurfaces involve bonding the substrate side of the metasurface to the fiber core end face. The presence of the substrate introduces an unnecessary optical path length, resulting in lower production efficiency and integration density compared to other processes. Therefore, there is an urgent need to provide a fiber core end face metasurface integration process with higher efficiency and integration density. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing metasurfaces on the end face of an optical fiber core.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution: A method for fabricating a metasurface on the end face of an optical fiber core includes the following steps: S1. Coat the surface of the copper sacrificial layer with photoresist, expose it to form a metasurface patterned groove, deposit TiO2, and then remove the TiO2 on the surface of the photoresist to obtain the TiO2 metasurface; S2. The TiO2 metasurface obtained in step S1 is bonded to the end face of the optical fiber core using UV-curable adhesive to form an integrated structure; the TiO2 metasurface completely covers the end face of the optical fiber core. S3. Immerse the integrated structure obtained in step S2 in FeCl3 solution to remove the copper sacrificial layer, thereby preparing a metasurface on the end face of the optical fiber core.

[0007] To address the challenge of directly integrating all-dielectric metasurfaces with fiber optic end faces, this invention utilizes an indirect transfer method. A copper layer serves as a sacrificial layer, providing a substrate for the metasurface to adhere to. This ensures the metasurface structure remains stable and does not collapse during fabrication and transfer. Furthermore, the copper sacrificial layer can be removed by immersion in a FeCl3 solution, preventing it from affecting the optical path of the fiber optic end face metasurface. Thus, this invention allows the front side of the TiO2 metasurface (the side furthest from the substrate and copper sacrificial layer) to adhere to the fiber optic end face. This process improves the efficiency and integration of indirect transfer while reducing the processing difficulties of direct manufacturing.

[0008] Preferably, the thickness of the copper sacrificial layer in step S1 is 200-400 nm.

[0009] Preferably, the photoresist in step S1 comprises chloromethacrylate-methylstyrene copolymer.

[0010] Preferably, the coating in step S1 is performed by spin coating, with a spin coating speed of 2000-4000 rpm and a time of 30-90 s.

[0011] More preferably, step S1 further includes a heat treatment step after coating, wherein the heat treatment temperature is 150-200℃ and the time is 3-5 min.

[0012] Preferably, the thickness of the photoresist coating in step S1 is 200-500 nm.

[0013] In a specific embodiment of this application, the depth of the metasurface pattern groove is consistent with the thickness of the photoresist.

[0014] Preferably, the exposure energy in step S1 is 80-120 keV, and the electron beam dose is 300-700 μC / cm. 2 .

[0015] Preferably, step S1 further includes a development step after exposure, wherein the development includes: immersion in ethyl acetate for 50-150 s, followed by immersion in a mixed solvent of methyl isobutyl ketone / isopropanol for 5-15 s.

[0016] More preferably, the volume ratio of methyl isobutyl ketone to isopropanol in the methyl isobutyl ketone / isopropanol mixed solvent is (8-10):1.

[0017] Preferably, the opening area of ​​the metasurface patterned groove in step S1 is 1000-2000 nm. 2 The distance between any two adjacent grooves is 400-1000 nm.

[0018] Preferably, TiO2 is deposited using atomic layer deposition in step S1.

[0019] More preferably, the atomic layer deposition process uses tetrakis(dimethylamino)titanium as the reaction precursor, H2O as the oxidant, and N2 as the purge gas.

[0020] More preferably, the flow rate of the purging gas is 5-15 sccm.

[0021] Preferably, step S1 uses reactive plasma etching to remove TiO2 from the photoresist surface. The reactive plasma etching is performed in an SF6 / Ar mixed atmosphere, wherein the flow rate of SF6 is 10-20 sccm and the flow rate of Ar is 15-25 sccm.

[0022] The inventors of this application have discovered that specific operations of atomic layer deposition and reactive plasma etching are more compatible with the process of this application, which can further facilitate the preparation and transfer integration of metasurfaces in this application.

[0023] Preferably, the UV-curing adhesive in step S2 is an acrylate-based curing adhesive.

[0024] More preferably, in step S2, the UV-curable adhesive is cured by irradiation with 350-450 nm UV light for 5-15 s.

[0025] Preferably, the concentration of the FeCl3 solution in step S3 is 3.5-4.5 mol / L.

[0026] Preferably, the soaking time in step S3 is 10-20 h.

[0027] Compared with the prior art, the present invention has the following beneficial effects: The main advantages of this invention are: first, compared with the processing method of directly preparing metasurfaces on the fiber end face, the process is simple and does not require size modification of the processing equipment; second, compared with the existing indirect transfer fiber end face metasurface processing method, it can realize the non-destructive structural transfer of TiO2 metasurfaces, eliminate the extra optical path caused by the substrate, and improve the integration. Attached Figure Description

[0028] Figure 1 This is a schematic flowchart of the method for preparing a metasurface on the end face of an optical fiber core provided by the present invention.

[0029] Figure 2 This is the initial GDS layout of the TiO2 metasurface provided in Embodiment 1 of the present invention.

[0030] Figure 3 (a) Physical image and (b) Optical micrograph of the TiO2 metasurface provided in Embodiment 1 of the present invention.

[0031] Figure 4 This is a SEM image of the TiO2 metasurface provided in Embodiment 1 of the present invention.

[0032] Figure 5 This is a schematic flowchart of the method for preparing a metasurface on the end face of an optical fiber core provided in Comparative Example 3 of the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents. Information on the raw materials used in some embodiments and comparative examples is as follows: ZEP adhesive: α-chloromethacrylate-α-methylstyrene copolymer, purchased from Zeon Chemicals, brand name Zep520A.

[0034] PMMA Glue-1: Purchased from MICRO CHEM, grade PMMA A4.

[0035] PMMA Glue-2: Purchased from MICRO CHEM, grade PMMA A2.

[0036] UV-curable adhesive-1: Acrylic ester adhesive, Kraft K-3181, purchased from Guangdong Kraft New Material Technology Co., Ltd.

[0037] UV-curable adhesive-2: Epoxy resin adhesive, brand name UV8580, purchased from Beijing Lienhe Communication Technology Co., Ltd.

[0038] FeCl3 solution: Dissolve FeCl3 in water to prepare a FeCl3 solution with a concentration of 4.05 mol / L.

[0039] Chromium removal solution: 1.16 g / mL high-purity cerium ammonium nitrate-based chromium etching solvent, Ce(NH4)2(NO3)6, purchased from Sigma-Aldrich.

[0040] Adhesive remover: Remover PG stripper, the main component of which is N-methyl-2-pyrrolidone, purchased from MICRO CHEM.

[0041] Example 1 A method for fabricating a metasurface on the end face of an optical fiber core includes the following steps: S1. A copper sacrificial layer was thermally deposited onto a cleaned ITO glass substrate using a thermal evaporation deposition machine with a deposition rate of 1.5 Å / s and a substrate film thickness of 300 nm. ZEP adhesive was then uniformly coated using a spin coater at 3000 rpm for 60 s, resulting in an adhesive thickness of 360 nm. After spin coating, the substrate was heated at 180°C for 4 minutes to allow excess solvent in the adhesive to evaporate. Electron beam lithography was then performed at 100 keV energy with a deposition rate of 500 μC / cm². 2 Electron beam exposure was used to form the desired metasurface pattern grooves. This was followed by development with ethyl acetate for 90 seconds and fixing with a mixed solvent of methyl isobutyl ketone (MIBK):isopropanol (IPA) = 9:1 (volume ratio) for 10 seconds. Then, TiO2 nanopillars were deposited using atomic layer deposition (ALD) with tetrakis(dimethylamino)titanium as the precursor and H2O as the oxidant, purged with nitrogen at a flow rate of 10 sccm. After deposition, the metasurface pattern grooves of the ZEP resin were filled with TiO2, and a 200 nm thick TiO2 layer covered the ZEP resin surface. Reactive plasma etching was used to etch the 200 nm thick TiO2 layer covering the ZEP resin surface, thus obtaining the TiO2 metasurface. The reactive plasma etching used an SF6 flux of 15 sccm and an Ar flux of 20 sccm. The openings of the metasurface pattern grooves were squares with dimensions of 400 nm * 400 nm, and the distance between any two adjacent squares was 600 nm. nm (this distance is the distance between the two nearest parallel sides of adjacent squares), and the depth of the grooves in the metasurface pattern is 360 nm; S2. Apply UV-curable adhesive-1 to the end face of the optical fiber core, then bring the side of the TiO2 metasurface without substrate perpendicular to the end face of the optical fiber core and irradiate it with 395 nm UV light for 10 seconds to cure the adhesive layer and form an integrated structure; the TiO2 metasurface completely covers the end face of the optical fiber core. S3. After immersing the integrated structure obtained in step S2 in a 4.05 mol / L FeCl3 aqueous solution for 12 h, the copper sacrificial layer is fully dissolved, and a metasurface can be prepared on the end face of the optical fiber core.

[0042] Example 2 A method for fabricating metasurfaces on the end face of an optical fiber core, wherein the only difference from Example 1 is: In step S1, inductively coupled plasma etching (ICP) is used to remove TiO2 with a thickness of 200 nm on the ZEP adhesive surface. In the inductively coupled plasma etching, the ICP source power is 400 W, the RF bias power is 80 W, the gas pressure is 8 mTorr, the SF6 flux is 15 sccm, and the Ar flux is 20 sccm.

[0043] Example 3 A method for fabricating metasurfaces on the end face of an optical fiber core, wherein the only difference from Example 1 is: In step S1, TiO2 is deposited using electron beam evaporation, which includes the following steps: First, the TiO2 target and sample are placed in the electron beam evaporation machine, followed by coarse and fine extraction to a depth of 5×10⁻⁶. -7 Below Torr, the high voltage and electron gun are turned on and the current power is slowly increased until the source material deposition rate is 0.6 Å / s. The sample baffle is turned on to start the evaporation. After the TiO2 layer thickness on the ZEP adhesive surface reaches 200 nm, the sample baffle is turned off, the power is reduced, and the high voltage is turned off to complete the electron beam evaporation.

[0044] Comparative Example 1 A method for fabricating metasurfaces on the end face of an optical fiber core, wherein the only difference from Example 1 is: In step S1, the copper sacrificial layer is replaced with a chromium sacrificial layer of equal thickness. For the chromium sacrificial layer, electron beam evaporation is used instead of thermal evaporation. First, the chromium metal target and sample are placed in the electron beam evaporation machine, and then rough and fine evaporation are performed to a thickness of 5×10⁻⁶. -7 Below Torr, the high voltage is turned on and the electron gun is slowly increased to the source material deposition rate of 0.5 Å / s. The sample baffle is turned on to start the evaporation. After reaching 300 nm, the sample baffle is turned off, the power is reduced, and the high voltage is turned off to complete the electron beam evaporation. In step S3, the chromium sacrificial layer is removed using a chromium removal solution.

[0045] Comparative Example 2 A method for fabricating metasurfaces on the end face of an optical fiber core, wherein the only difference from Example 1 is: In step S1, the copper sacrificial layer is replaced with a PMMA sacrificial layer of equal thickness. The method for preparing the PMMA sacrificial layer includes the following steps: PMMA adhesive-1 was coated on the surface of an ITO substrate and then uniformly coated at 2000 rpm for 60 s in a spin coater to obtain a 300 nm thick PMMA sacrificial layer. The coating was then heated at 180 °C for 30 min.

[0046] Comparative Example 3 A method for fabricating metasurfaces on the end face of an optical fiber core, wherein the only difference from Example 1 is: In step S1, an etching process is used to prepare a TiO2 metasurface to complete the preparation of the metasurface, specifically including the following steps: A 300 nm thick copper sacrificial layer was thermally deposited on a cleaned ITO glass substrate. Following this, an 850 nm thick TiO2 dielectric film was deposited on the copper sacrificial layer using electron beam evaporation (EB / LD) with a deposition rate of 0.6 Å / s. PMMA-2 was then spin-coated at 2000 rpm for 60 s, followed by pre-baking at 180 °C for 30 min. Electron beam lithography was then employed using an electron beam energy of 30 keV and a temperature of 900 μC / cm². 2 The PMMA resin-2 was patterned using an electron beam dose, followed by development for 60 s using a mixed solvent of methyl isobutyl ketone (MIBK) and isopropanol (IPA) at a ratio of 1:3 (volume ratio), then fixed with IPA solution for 10 s. After drying with nitrogen, a 30 nm thick layer of metallic chromium was deposited by electron beam evaporation as a hard mask. The chromium was then patterned by stripping at 80°C for 24 h using a resist stripper. The TiO2 film was then etched using a mixed gas containing SF6, CHF3, and O2 via reactive plasma etching. During etching, the RF power was set to 100 W and the pressure to 9 mTorr. The CHF3 / SF6 ratio was 5.5. Finally, the chromium hard mask was removed using a chromium stripper to obtain a TiO2 nanopillar array.

[0047] The process of step S1 in the method provided in this comparative example is as follows: Figure 5 As shown.

[0048] Comparative Example 4 A method for fabricating metasurfaces on the end face of an optical fiber core, wherein the only difference from Example 1 is: In step S1, a copper sacrificial layer is not thermally deposited on the ITO glass substrate as a sacrificial layer, and subsequent steps are carried out directly.

[0049] In step S2, the side of the TiO2 metasurface containing the substrate is brought close to the fiber core end face perpendicularly.

[0050] Process Feasibility Test and Analysis The feasibility test and analysis results of the processes provided in the above embodiments and comparative examples are shown in Table 1 below: Table 1.

[0051] As can be seen from the results in Table 1 above, the process provided by the present invention can integrate metasurfaces on the end face of optical fiber core in a simple way, and can realize the non-destructive structural transfer of TiO2 metasurfaces, eliminating the additional optical path caused by the substrate.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for fabricating a metasurface on the end face of an optical fiber core, characterized in that, Includes the following steps: S1. Coat the surface of the copper sacrificial layer with photoresist, expose it to form a metasurface patterned groove, deposit TiO2, and then remove the TiO2 on the surface of the photoresist to obtain the TiO2 metasurface; S2. The TiO2 metasurface obtained in step S1 is bonded to the end face of the optical fiber core using UV-curable adhesive to form an integrated structure; the TiO2 metasurface completely covers the end face of the optical fiber core. S3. Immerse the integrated structure obtained in step S2 in FeCl3 solution to remove the copper sacrificial layer, and a metasurface can be prepared on the end face of the optical fiber core.

2. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, The photoresist in step S1 includes chloromethacrylate-methylstyrene copolymer.

3. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, The thickness of the photoresist coating in step S1 is 200-500 nm.

4. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, The exposure step S1 further includes a development step, which includes: immersing in ethyl acetate for 50-150 s, followed by immersing in a mixed solvent of methyl isobutyl ketone / isopropanol for 5-15 s.

5. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, The opening area of ​​the metasurface patterned groove in step S1 is 1000-2000 nm. 2 The distance between any two adjacent grooves is 400-1000nm.

6. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, In step S1, TiO2 is deposited using atomic layer deposition (ALD). Preferably, the precursor used in ALD is tetrakis(dimethylamino)titanium, the oxidant is H2O, and the purging gas is N2.

7. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, Step S1 uses reactive plasma etching to remove TiO2 from the photoresist surface. The reactive plasma etching is performed in an SF6 / Ar mixed atmosphere, wherein the flow rate of SF6 is 10-20 sccm and the flow rate of Ar is 15-25 sccm.

8. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, The UV-curable adhesive mentioned in step S2 is an acrylate-based curable adhesive.

9. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1, characterized in that, The concentration of the FeCl3 solution in step S3 is 3.5-4.5 mol / L.

10. The method for preparing a metasurface on the end face of an optical fiber core as described in claim 1 or 9, characterized in that, The soaking time in step S3 is 10-20 hours.

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