In-situ preparation method and application of metastructure surface device on D-type optical fiber

Abstract

The invention relates to the field of metamaterial technology and optical fiber integrated devices, and discloses an in-situ preparation method and application of a metastructure surface device on a D-type optical fiber. Carrying out integration and planar integration on the optical fiber and a standard quartz substrate by utilizing a grinding process to obtain a quartz substrate which is embedded with the D-type optical fiber and is compatible with a standard electron beam exposure system; the designed super-structure surface structure is prepared on the D-shaped surface of the optical fiber in situ by using standard electron beam exposure, coating and stripping processes, and the super-structure surface device integrated on the side surface of the optical fiber is obtained. According to the method, the gold nanorod metasurface mode locker is prepared on the D-type optical fiber, and the device is welded in an all-optical-fiber ring cavity laser to realize femtosecond pulse laser output. The invention provides a brand-new optical fiber integration application platform and a preparation method for the metasurface. The D-type optical fiber upper metasurface mode locker prepared by the method is a novel all-optical fiber mode locking device and is expected to become a substitute of a commercial semiconductor saturable absorber mirror mode locking device.

Description

Technical Field

[0001] The present invention relates to the field of metamaterial technology and optical fiber integrated device technology, and in particular to an in-situ preparation method and application of a metasurface device on a D-type optical fiber. Background Art

[0002] Optical metasurfaces are artificially designed optical functional materials or devices whose basic units are on the subwavelength scale. By manipulating the geometric structure and arrangement of these units, parameters such as the phase, amplitude, and polarization of light can be precisely controlled. The emergence of metasurfaces has overcome the limitations of traditional optical materials and opened up a new paradigm in the research and application of photonic devices. With the continuous improvement of design theory and micro-nanofabrication technology, metasurfaces are expected to achieve wider application in new optoelectronic devices, quantum optics, photonic integrated circuits, and other fields, promoting innovation and development in optical imaging and control technologies.

[0003] Optical metasurfaces typically have geometric dimensions ranging from micrometers to millimeters and are micro-nanophotonic devices. However, the optoelectronic systems currently in widespread use are based on traditional bulk optoelectronic components. Therefore, efficient integration of metasurfaces with traditional optoelectronic components and systems is essential for their practical application. Currently, by integrating metasurfaces with imaging components, metasurface imaging cameras and metamicroscopes have been developed; by integrating metasurfaces with photodetectors, high-sensitivity and wide-band photodetectors have been developed; and by integrating metasurfaces with lasers, structured light field lasers have been developed. The integrated application of metasurfaces with traditional optoelectronic devices or systems, such as imaging components, photodetectors, and lasers, has brought disruptive technological breakthroughs to related fields.

[0004] Optical fiber, as a common optical transmission medium and waveguide in integrated optical devices, plays a key role in applications such as fiber-optic communications, sensing, and lasers. Continuous advances in fiber-optic integrated optical devices have made fiber-optic communications, sensing, and laser systems more efficient, reliable, and diverse. Due to the incompatibility of optical fibers with existing standard micro-nanofabrication systems, the in-situ fabrication of metasurfaces directly on optical fibers faces challenges. In-situ fabrication refers to the direct generation of materials or structures at the target location and is an advanced fabrication method and concept that eliminates the handling, transfer, and assembly steps required in traditional processes. Currently, the application of metasurfaces in optical fiber systems often requires coupling and assembling a planar substrate metasurface with the optical fiber via a spatial optical system, resulting in low integration, efficiency, and stability. To address this issue, researchers in Chinese patent CN116413928A and prior art have proposed a focused ion beam-based direct fabrication process for optical fiber end faces. The large sample stage working distance of a focused ion beam system allows for in-situ fabrication of metasurface microstructures on upright optical fiber end faces. However, precise control of machining accuracy and depth is difficult, and generally only shallow nanopore structures can be fabricated, not deep nanorod / pillar structures. Since then, researchers have developed a nanoimprint-based in-situ fabrication process for metasurfaces on optical fiber end faces. This technology supports metasurfaces with basic units at the micron level, which cannot meet the requirements for preparing metasurfaces with smaller basic units and cannot be applied to shorter wavelengths. The two aforementioned technical methods provide feasible approaches for the in-situ fabrication of metasurfaces on optical fiber end faces. However, the in-situ fabrication of metasurfaces on the sides of optical fibers remains unresolved. The core difficulty lies in the incompatibility of optical fibers with existing standard micro-nanofabrication systems (such as electron beam lithography and photolithography).

[0005] Based on this, the present invention proposes an in-situ preparation method for metasurface devices on D-type optical fibers, and verifies its application in optical fiber lasers. Summary of the Invention

[0006] The present invention discloses an in-situ preparation method and application of a metasurface device on a D-type optical fiber, aiming to solve the following technical problems involved in the in-situ preparation of a metasurface device on the side of an optical fiber:

[0007] (1) Compatibility issues between optical fiber and electron beam lithography system: The electron beam lithography system is only compatible with planar substrate samples during positioning and focusing. If the substrate to be processed is non-planar, it will lead to inaccurate positioning and focusing, resulting in distortion of the etched pattern. The optical fiber is a cylindrical structure with a large aspect ratio, and its side is a cylindrical surface, which is a non-planar substrate.

[0008] (2) Non-uniformity problem of electron beam photoresist: If the upper and lower surfaces of the planar substrate are not flat, the thickness of the photoresist applied to the substrate surface will be inconsistent during the photoresist spreading process, affecting the etching depth and accuracy;

[0009] (3) The problem of optical fiber falling off from the quartz substrate during the stripping process: If the optical fiber curing glue is miscible with the solution selected in the stripping step, the optical fiber will detach from the quartz substrate or even break during the stripping process.

[0010] This application prepares the metasurface in situ on the side of an optical fiber (such as a D-type optical fiber) to obtain an all-fiber integrated metasurface device, which will provide a new platform for the interaction between light and matter for linear and nonlinear light field control, thereby bringing new opportunities for fiber optic sensing, fiber lasers, nonlinear optics, etc., and also provide new ideas for the integrated application of metasurfaces.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present application provides an in-situ preparation method for a metasurface device on a D-type optical fiber, the method comprising the following steps:

[0013] Step S1: preparing a D-type optical fiber on a quartz substrate;

[0014] Step S2: performing a first pretreatment on the D-type optical fiber quartz substrate;

[0015] Step S3: performing electron beam exposure on the first pre-treated D-type optical fiber quartz substrate using a predefined metasurface structure pattern;

[0016] Step S4: performing developing and fixing operations;

[0017] Step S5: After performing a second pretreatment on the D-type optical fiber quartz substrate, a metasurface device integrated on the D-type optical fiber is obtained.

[0018] Furthermore, in step S1, the process of preparing the D-type optical fiber is as follows:

[0019] Step S11: placing a single-mode optical fiber in a quartz V-groove, and curing the optical fiber and the quartz V-groove substrate with epoxy resin glue;

[0020] Step S12: grinding and polishing the fixed area of ​​the single-mode optical fiber to obtain a D-type optical plane of the optical fiber to make a D-type optical fiber; the D-type optical fiber quartz substrate is used as the substrate to be processed, and the D-type optical plane of the optical fiber is used as the pattern etching area.

[0021] Furthermore, in step S2, the first preprocessing process includes:

[0022] Step S21: Cleaning the D-type optical fiber quartz substrate;

[0023] Step S22: Spin-coating photoresist and conductive adhesive on the cleaned D-type optical fiber quartz substrate.

[0024] Furthermore, in step S21, the cleaning solution is selected from a paraffin removal solution and an isopropyl alcohol solution; after the solution is cleaned and before the photoresist and the conductive adhesive are spin-coated, the steps of drying the solution and heating the solution on a heating platform are also included.

[0025] Furthermore, in step S22, an electron beam photoresist is spin-coated on the upper surface of a D-type optical fiber quartz substrate using a coating machine. After spin coating to form a film, it is annealed on a heating table. The specific annealing operation is heating on a heating table at 180°±2° for 10 to 15 minutes; then, a conductive glue is spin-coated on the upper layer, and a secondary annealing is performed on the heating table, and heating is continued on the heating table at 180°±2° for 10 to 15 minutes; the thickness of the photoresist is 400~500 nm, and the thickness of the conductive glue is 400~500 nm.

[0026] Furthermore, in step S3, the metasurface structure pattern is a microstructure array, and an electron beam exposure system is used to transfer the pattern into the photoresist.

[0027] Furthermore, in step S4, before performing the developing and fixing operation, the D-type optical fiber quartz substrate is first immersed in deionized water to remove the upper conductive glue; it is developed in a developer to remove the photoresist in the metasurface structure pattern part, and then fixed.

[0028] Furthermore, in step S5, the second preprocessing process includes:

[0029] Step S51: performing metal film evaporation on the upper surface of the D-type optical fiber quartz substrate;

[0030] Step S52: After the metal film is evaporated, it is immersed in a solvent to perform degumming and stripping operations.

[0031] In a second aspect, the present application provides a metasurface device integrated on a D-type optical fiber, which is prepared using the in-situ preparation method provided in the first aspect above.

[0032] In a third aspect, the present application provides the application of the above-mentioned metasurface device integrated on a D-type optical fiber as a mode-locked device in a fiber laser for generating femtosecond pulse lasers.

[0033] Technical effects:

[0034] Compared to existing technologies, the present invention provides a metasurface device integrated on a D-type optical fiber, a preparation method, and its application. The optical fiber and a standard quartz substrate are integrated and planarized using a grinding process to obtain a quartz substrate with an embedded D-type optical fiber that is compatible with a standard electron beam lithography system. The designed metasurface pattern is then in situ fabricated on the D-shaped surface of the optical fiber using standard electron beam lithography, coating, and stripping processes, resulting in a fully fiber-integrated metasurface device. This technology has the following technical effects:

[0035] 1. This application combines metasurfaces with optical fibers and uses standard electron beam lithography, coating, and stripping processes to in situ fabricate a fully fiber-integrated metasurface device on a D-type optical fiber. This solves the compatibility issue of directly fabricating metasurfaces on the side of an optical fiber using electron beam lithography, and provides a new platform for the integrated fabrication and application of metasurfaces.

[0036] 2. This application fixes an ordinary single-mode optical fiber in a quartz V-groove substrate and grinds out a D-shaped polishing area, making the entire optical fiber sample planar and compatible with a standard electron beam exposure system, greatly reducing the focusing and positioning problems in electron beam etching processing.

[0037] 3. To address the problem of non-uniformity of electron beam photoresist, this application uses a deparaffinized solution and an isopropyl alcohol solution to clean the polished quartz substrate with the embedded D-type optical fiber, ensuring that the upper and lower surfaces of the substrate are flat and clean. In addition, to address the problem of the optical fiber falling off the quartz V-groove substrate during the stripping process, epoxy resin glue is used as the optical fiber curing glue. The epoxy resin glue is strictly proportioned and cured at elevated temperature, so that the optical fiber will not detach or break from the quartz V-groove substrate during the stripping process.

[0038] 4. This application also provides a metasurface device integrated on a D-type optical fiber as a mode-locking device in an optical fiber laser to generate femtosecond pulse lasers. Figure 7-10 The application verification shows that the modulation depth of the fiber-integrated metasurface mode locker is 26.3%, and the femtosecond pulse laser it generates has good stability, a pulse interval of 74 ns, and a pulse width of 439 fs. The metasurface device on the D-type fiber is fused into the fiber laser as a mode locker to form an all-fiber structure mode-locked laser, which has the characteristics of high integration and good stability and can generate high-quality femtosecond pulse lasers. In addition, the metasurface mode locker on the D-type fiber has the advantages of lower insertion loss and higher fiber integration, providing a new way for all-fiber integration of high-performance metasurface mode-locked devices. This device is a new type of all-fiber mode locker and is expected to become a substitute for commercial semiconductor saturable absorber mirror mode-locked devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Flowchart of the in-situ fabrication method for a metasurface device on a D-type optical fiber provided by an embodiment of the present invention.

[0040] Figure 2 This is a structural model diagram of the D-type optical fiber metasurface device provided in an embodiment of the present invention.

[0041] Figure 3 This is a flow chart for preparing a D-type optical fiber on a quartz substrate provided by an embodiment of the present invention.

[0042] Figure 4Flow chart for preparing a metasurface on a D-type optical fiber according to an embodiment of the present invention.

[0043] Figure 5 This is a scanning electron microscope image of a metasurface device on a D-type optical fiber provided by an embodiment of the present invention.

[0044] Figure 6 This is a saturable absorption curve of the metasurface device on a D-type optical fiber provided by an embodiment of the present invention.

[0045] Figure 7 A schematic structural diagram of a fiber laser device according to an embodiment of the present invention.

[0046] Figure 8 This is a diagram of the output laser pulse sequence of the fiber laser used in the device provided in an embodiment of the present invention.

[0047] Figure 9 This is a diagram of the output laser spectrum of the fiber laser used in the device provided in an embodiment of the present invention.

[0048] Figure 10 This is a diagram of the autocorrelation trajectory of the output laser of the fiber laser used in the device provided in an embodiment of the present invention.

[0049] Reference numerals:

[0050] 1-metasurface device; 11-single-mode optical fiber; 12-quartz substrate; 13-metasurface; 14-V-groove; 15-D-shaped surface;

[0051] 2-D optical fiber quartz substrate; 21-fiber core; 22-cladding; 23-epoxy resin glue;

[0052] 31-photoresist; 32-conductive adhesive; 33-electron beam exposure area; 34-metal film; 35-gold nanorod array;

[0053] 41-pump source; 42-wavelength division multiplexer; 43-gain fiber; 44-polarization-independent isolator; 45-output coupler; 46-mode locker; 47-polarization controller. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0055] Example 1:

[0056] The present invention discloses an in-situ preparation method of a D-type optical fiber metasurface device, referring to Figure 1 The working principle process of the preparation method is as follows:

[0057] Step S1: preparing a D-type optical fiber on a quartz substrate 12;

[0058] Step S2: performing a first pretreatment on the D-type optical fiber quartz substrate 2;

[0059] Step S3: performing electron beam exposure on the first pre-treated D-type optical fiber quartz substrate 2 using a predefined metasurface structure pattern;

[0060] Step S4: performing developing and fixing operations;

[0061] Step S5: After performing a second pretreatment on the D-type optical fiber quartz substrate 2 , a metasurface device 1 integrated on the D-type optical fiber is obtained.

[0062] Specifically, if Figure 1-4 As shown, the process of the above preparation method is specifically as follows:

[0063] Step S1: preparing a D-type optical fiber on a quartz substrate 12;

[0064] In a specific embodiment of the present invention, the size of the quartz substrate 12 is 2×3 cm, and a V-groove 14 is engraved in the middle of the quartz substrate 12 for placing the single-mode optical fiber 11 with the coating stripped off. Figure 3 As shown, a single-mode optical fiber is fixed within a quartz V-groove 14 using optical fiber curing adhesive. The optical fiber curing adhesive can be epoxy resin adhesive 23 or another similar adhesive. The central region is polished to form a D-shaped surface 15 (polished area), resulting in a D-shaped optical fiber quartz substrate 2. The quartz substrate with the embedded D-shaped optical fiber is defined as the substrate to be processed, with the polished area of ​​the D-shaped optical fiber serving as the optical plane for etching the metasurface pattern. In conjunction with the above, a D-shaped optical fiber is defined as an optical fiber with a D-shaped optical plane produced by fixing a conventional single-mode optical fiber within a quartz V-groove 14 and then polishing the fixed area.

[0065] It is worth noting that a grinding device such as a grinder is used to grind the D-type optical fiber fixed area, where the fixed area can be used as the polishing area of ​​the D-type optical fiber. In the process of obtaining the D-shaped surface of the optical fiber, the polished area of ​​the D-type optical fiber fixed on the quartz substrate 12 is used as the substrate to be processed, making the entire system planar. The electron beam exposure system is only compatible with planar substrates during positioning and focusing. If the substrate is non-planar, it will lead to inaccurate positioning and focusing, resulting in distortion of the etched pattern. The D-type optical fiber quartz substrate 2 prepared by this process greatly reduces the focusing and positioning problems of electron beam etching processing in subsequent steps. After testing with a step profiler, its surface flatness can be controlled in the range of 10~15 nm, meeting the requirements of subsequent processing.

[0066] Steps S2-S5 are the process of in-situ preparation of metasurface on D-type optical fiber. Figure 4As shown: a metasurface 13 is prepared in situ on a D-shaped surface using standard electron beam exposure, development / fixing, coating, and stripping processes. This step includes: film washing and coating (photoresist 31, conductive adhesive 32), electron beam exposure, development and fixing, thermal evaporation coating (metal film 34), and stripping.

[0067] Specifically, step S2: performing a first pretreatment on the D-type optical fiber quartz substrate 2;

[0068] Step S21: Rinse the D-type optical fiber quartz substrate 2 with a deparaffinizing solution and isopropyl alcohol to ensure that the upper and lower surfaces are smooth and clean. Then, air dry the substrate and heat it on a hot plate or other heating surface. This cleaning process further ensures the smoothness of the upper and lower surfaces of the substrate, effectively overcoming the unevenness of the electron beam photoresist 31 and the conductive adhesive 32.

[0069] Step S22: Spin-coat an electron beam photoresist 31 onto the upper surface of the D-type optical fiber quartz substrate 2 to a thickness of 400-500 nm. After spin-coating, anneal the film on a hot plate at a temperature of 180° ± 2° for 10-15 minutes. Then, spin-coat a conductive adhesive 32 on top to a thickness of 400-500 nm. Finally, perform a second annealing on the hot plate, heating at a temperature of 180° ± 2° for 10-15 minutes. This completes the first pretreatment process for the D-type optical fiber quartz substrate 2.

[0070] Step S3: Electron beam exposure is performed on the upper surface of the D-type optical fiber quartz substrate 2 after the first pretreatment using a predefined metasurface structure pattern to form an electron beam exposure area 33, and the pattern is transferred to the photoresist 31. A planar positioning and focusing reference is obtained through step S1, and uniform substrate flatness is obtained through step S2, ensuring accurate writing by the electron beam exposure system. Here, the upper surface of the D-type optical fiber quartz substrate 2 is the polished surface of the quartz substrate with the D-type optical fiber embedded therein, and the metasurface structure pattern is a microstructure array.

[0071] Step S4: performing developing and fixing operations;

[0072] Specifically, the D-type optical fiber quartz substrate 2 is first immersed in deionized water to remove the upper conductive glue 32; developed in a developer to remove the photoresist 31 of the metasurface pattern portion, and then placed in isopropyl alcohol for fixing.

[0073] Step S5: After performing a second pretreatment on the D-type optical fiber quartz substrate 2, a D-type optical fiber metasurface device 1 is obtained.

[0074] Specifically, step S51: evaporating a metal film 34 on the upper surface of the D-type optical fiber quartz substrate 2. The clean D-type optical fiber quartz substrate 2 is placed in a thermal evaporation chamber, and chromium and gold thin films are sequentially evaporated.

[0075] Step S52: Debonding and stripping the metal-deposited D-type optical fiber quartz substrate 2. Specifically, the coated substrate is immersed in a solvent, preferably 1-methyl-2-pyrrolidone, to remove the remaining photoresist 31 on the surface. If necessary, the residual surface liquid is further rinsed with deionized water. This results in a gold nanorod array 35 on the surface of the D-type optical fiber quartz substrate 2, thus obtaining the D-type optical fiber metasurface device 1.

[0076] Example 2:

[0077] The embodiment of the present invention provides a D-type optical fiber metasurface device prepared by the preparation method of Example 1. The scanning electron microscope image of the final D-type optical fiber metasurface device is as follows: Figure 5 shown. Figure 6 Shown is a saturable absorption curve of a metasurface device on a D-type optical fiber provided by an embodiment of the present disclosure.

[0078] Example 3:

[0079] The embodiment of the present invention provides an application of the device as a mode locker 46 to generate femtosecond pulse laser in a fiber laser. Figure 7 Shown is a schematic structural diagram of a device provided by an embodiment of the present disclosure applied to a fiber laser.

[0080] like Figure 7 As shown, the fiber laser device is an all-fiber ring cavity structure, including a pump source 41, a wavelength division multiplexer 42, a gain fiber 43, a polarization-independent isolator 44, an output coupler 45, a metasurface mode locker 46 on a D-type fiber, and a polarization controller 47. These components are connected sequentially along the laser's transmission direction (clockwise), with the input end of the gain fiber 43 connected to the output ends of the pump source 41 and the polarization controller 47, respectively, via the wavelength division multiplexer 42. The metasurface device on the D-type fiber acts as the mode locker 46, achieving passive mode locking and generating femtosecond pulse laser light.

[0081] The above-mentioned devices are connected by fiber fusion splicing to form an all-fiber laser resonator. At the same time, passive mode locking is achieved by using a metasurface device on a D-type optical fiber as a mode locker 46. The basic principle of passive mode locking is to introduce the mode locker 46 into the optical path. When the signal light noise pulse excited by the pump light passes through the mode locker 46, the strong pulse is retained and continuously amplified by the gain fiber, while the weak pulse is attenuated. At the same time, the loss at the edge of the pulse is greater than that at the center, causing the optical pulse to narrow. Under the dual effects of the mode locker on pulse selection and narrowing, ultrashort pulse lasers, such as femtosecond pulse lasers, are formed. The constructed mode-locked fiber laser device is an all-fiber structure with the advantages of high integration and good stability. It can generate femtosecond ultrashort pulse lasers, which is conducive to more efficient and precise applications in fields such as materials processing and spectroscopy.

[0082] Figure 8 The figure shows the pulse sequence diagram of the D-type optical fiber metasurface mode locker provided by the embodiment of the present disclosure applied to the optical fiber laser, which outputs the laser at a pump power of 26 mW. Figure 8 As shown in Figure 3, the intracavity mode-locked pulse of the fiber laser device operates in a stable state with a pulse interval of 74 ns.

[0083] Figure 9 The figure shows the spectrum of the laser output when the D-type optical fiber metasurface mode locker provided by the embodiment of the present disclosure is applied to the optical fiber laser at a pump power of 26 mW. Figure 9 As shown, the central wavelength of the spectrum is 1565.0 nm.

[0084] Figure 10 The figure shows the autocorrelation trajectory of the laser output when the D-type optical fiber metasurface mode locker provided by the embodiment of the present disclosure is applied to the optical fiber laser at a pump power of 26 mW. Figure 10 As shown, the pulse width is 439 fs.

[0085] from Figures 6 to 10 It can be seen that the D-type fiber metasurface mode locker provided by the embodiments of the present disclosure, when applied to a fiber laser, has a modulation depth of 26.3%, a pulse interval of 74 ns, a pulse width of 439 fs, and good pulse stability. This demonstrates that D-type fiber metasurfaces can be used as mode lockers in the field of fiber lasers. The large modulation depth of the D-type fiber metasurface mode locker enables passive mode locking and produces femtosecond ultrashort pulse lasers.

[0086] Using this method, a gold nanorod metasurface mode locker was fabricated on a D-type optical fiber. This device was then fused to an all-fiber laser to achieve mode-locked femtosecond pulsed laser output. This approach addresses the process compatibility challenges associated with directly fabricating metasurfaces on optical fibers using electron beam lithography, providing a new platform and fabrication method for the integrated application of metasurfaces. The D-type optical fiber metasurface mode locker fabricated using this method represents a novel all-fiber mode-locking device with the potential to replace commercial semiconductor saturable absorber mirror mode-locking devices.

[0087] This application combines metasurfaces with optical fibers, and uses standard electron beam lithography, coating, stripping and other processes to in-situ prepare metasurface devices on D-type optical fibers. This solves the compatibility problem of directly preparing metasurfaces on optical fibers based on electron beam lithography, and provides a new platform for the integrated application of metasurfaces.

[0088] The present invention proposes an in-situ preparation method and application of metasurface devices on D-type optical fibers. An ordinary single-mode optical fiber is fixed in a quartz V-groove substrate, and a D-shaped polished area is ground out to make the optical fiber sample and the quartz substrate planar, which is compatible with standard electron beam exposure systems.

[0089] The present invention proposes an in-situ preparation method and application of a metasurface device on a D-type optical fiber, combining the metasurface with the optical fiber to prepare a fully optical fiber integrated metasurface device.

[0090] The present invention proposes an in-situ preparation method and application of metasurface devices on D-type optical fibers, demonstrates the design model and specific method for directly preparing metasurfaces on the side of optical fibers, solves the compatibility problem of directly preparing metasurfaces on the side of optical fibers based on electron beam lithography, and provides a new platform for the integrated application of metasurfaces.

[0091] Based on the above advantages, the present invention also provides an application of this device, in which the D-type fiber metasurface device is fused into a fiber laser as a mode locker, creating an all-fiber mode-locked fiber laser with high integration and excellent stability, capable of generating femtosecond pulses. Furthermore, the D-type fiber metasurface mode locker offers the advantages of lower insertion loss and higher fiber integration, providing a new approach to all-fiber integration for high-performance metasurface mode-locked devices, facilitating more efficient and precise applications in fields such as materials processing and spectroscopy.

[0092] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. The replacement may be a replacement of a portion of a structure, device, or method step, or it may be a complete technical solution. Any equivalent replacement or modification based on the technical solution and inventive concept of the present invention shall be covered by the scope of protection of the present invention.

Claims

1. An in-situ preparation method for a metasurface device on a D-type optical fiber, characterized in that: The method comprises the following steps: Step S1: preparing a D-type optical fiber on a quartz substrate; Step S2: performing a first pretreatment on the D-type optical fiber quartz substrate; Step S3: performing electron beam exposure on the first pre-treated D-type optical fiber quartz substrate using a predefined metasurface structure pattern; Step S4: performing developing and fixing operations; Step S5: After performing a second pretreatment on the D-type optical fiber quartz substrate, a metasurface device integrated on the D-type optical fiber is obtained.

2. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 1, characterized in that: In step S1, the process of preparing the D-type optical fiber is as follows: Step S11: placing a single-mode optical fiber in a quartz V-groove, and curing the optical fiber and the quartz V-groove substrate with epoxy resin glue; Step S12: grinding and polishing the fixed area of ​​the single-mode optical fiber to obtain a D-type optical plane of the optical fiber to make a D-type optical fiber; the D-type optical fiber quartz substrate is used as the substrate to be processed, and the D-type optical plane of the optical fiber is used as the pattern etching area.

3. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 2, characterized in that: In step S2, the first pre-processing process includes: Step S21: Cleaning the D-type optical fiber quartz substrate; Step S22: Spin-coating photoresist and conductive adhesive on the cleaned D-type optical fiber quartz substrate.

4. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 3, characterized in that: In the step S21, the cleaning solution is a paraffin removal solution and an isopropyl alcohol solution; after the solution is cleaned and before the photoresist and the conductive adhesive are spin-coated, the steps of drying the solution and heating the heating platform are also included.

5. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 3, characterized in that: In step S22, an electron beam photoresist is spin-coated on the upper surface of a D-type optical fiber quartz substrate using a coating machine. After the spin coating forms a film, it is annealed on a heating table. The specific annealing operation is heating on a heating table at 180°±2° for 10 to 15 minutes; then, a conductive adhesive is spin-coated on the upper layer, a secondary annealing is performed on the heating table, and heating is continued on the heating table at 180°±2° for 10 to 15 minutes. The thickness of the photoresist is 400~500 nm, and the thickness of the conductive adhesive is 400~500 nm.

6. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 3, characterized in that: In step S3, the metasurface structure pattern is a microstructure array, and an electron beam exposure system is used to transfer the pattern into the photoresist.

7. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 3, characterized in that: In step S4, before developing and fixing, the D-type optical fiber quartz substrate is immersed in deionized water to remove the upper conductive adhesive; it is developed in a developer to remove the photoresist of the metasurface structure pattern, and then fixed.

8. The in-situ preparation method of a D-type optical fiber metasurface device according to claim 1, characterized in that: In step S5, the second pre-processing process includes: Step S51: performing metal film evaporation on the upper surface of the D-type optical fiber quartz substrate; Step S52: After the metal film is evaporated, it is immersed in a solvent to perform degumming and stripping operations.

9. A metasurface device integrated on a D-type optical fiber, characterized in that: It is prepared by the in-situ preparation method according to any one of claims 1 to 8.

10. Use of the metasurface device integrated on a D-type optical fiber according to claim 9 as a mode-locked device in a fiber laser for generating femtosecond pulse lasers.

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