A structure and method for reducing transmission loss based on parallel silver nanowires

Abstract

The application belongs to the technical field of surface plasmon excitation and transmission application, and relates to a structure and method for reducing transmission loss based on parallel silver nanowires. The substrate is provided with at least one pair of parallel silver nanowires, the diameter of the silver nanowires is 400-800 nm, the length of the silver nanowires is 10-20 microns, and the parallel spacing or gap of the silver nanowire pair is 5-50 nm; the method comprises the following steps: step 1, preparing large-size silver nanowires; step 2, using a micro-manipulation method to accurately move a single silver nanowire on the substrate prepared in step 1 to construct a parallel silver nanowire structure; and step 3, using a fiber coupling method to excite the parallel silver nanowires to generate SPPs and measure the transmission loss. The application utilizes the influence of mode coupling between two parallel single silver nanowires in the parallel silver nanowire structure on the electric field distribution, suppresses the radiation leakage of energy to the substrate, and significantly reduces the transmission loss of SPPs.

Description

Technical Field

[0001] This invention belongs to the technical field of surface plasmon excitation and transmission applications, and relates to a structure and method for reducing transmission loss based on parallel silver nanowires. Background Technology

[0002] When light waves (electromagnetic waves) are incident on the interface between a metal and a dielectric, they can couple and excite collective oscillations of free electrons on the metal surface. In metal nanoparticles, these collective oscillations are limited by the particle size; these are called localized surface plasmons (LSPs). Surface plasmons excited at the interface between metal nanowires (thin films) and the dielectric can propagate long distances along the interface; these are called propagating surface plasmon polaritons (SPPs). This is a non-radiative electromagnetic mode with unique properties that break the optical diffraction limit, making it crucial for the development of on-chip optoelectronic integrated devices and possessing great application potential in ultra-sensitive detection, optical sensing, and information processing.

[0003] Silver nanowires (Ag NWs) are quasi-one-dimensional surface plasmon waveguide structures, commonly used as fundamental components in nanophotonic devices. Typically, silver nanowires have diameters ranging from tens to hundreds of nanometers, and lengths from hundreds of nanometers to hundreds of micrometers. Due to their unique physical and chemical properties, silver nanowires have shown potential applications in multiple fields. Various methods exist for preparing silver nanowires, including chemical synthesis and physical vapor deposition (PVD). Compared to physically prepared silver nanowires, chemically prepared silver nanowires exhibit a five-fold twinned structure with a regular morphology and smooth surface, thus significantly reducing energy loss caused by surface defect scattering, making them ideal materials for SPP waveguides. By modulating the SPPs propagating on silver nanowires, nanophotonic devices with different functions can be realized, including SPP routers, logic gates, nanolasers, and beam splitters. These photonic devices are compatible with dielectric waveguides, enabling their widespread application in nano-integrated photonic devices and circuits.

[0004] However, due to the strong field confinement properties of SPPs, the ohmic loss of the metal nanowires themselves is relatively large. Combined with radiation losses from SPPs into the surrounding medium, the energy loss during nanowire transmission remains significant. Previous research has mainly focused on reducing energy loss during transmission by introducing dielectric layers, two-dimensional materials, or gain materials between the silver nanowires and the substrate. These methods require additional dielectric layer structures, which complicates the fabrication process of nanophotonic devices and hinders the manipulation of the optical field.

[0005] Therefore, how to construct a simple waveguide structure to reduce the energy loss of SPPs during transmission on silver nanowires has become an urgent problem to be solved in the development of integrated photonic circuits and devices. Summary of the Invention

[0006] The technical solution adopted by this invention to solve the technical problem is: a structure based on parallel silver nanowires to reduce surface plasmon transmission loss. The structure consists of at least one pair of parallel silver nanowires on a substrate. The substrate generally has multiple nanowires, and the density of the nanowire distribution can be artificially controlled. The diameter of the silver nanowires is 400–800 nm, the length of the silver nanowires is 10–20 μm, and the parallel spacing or gap between the pairs of silver nanowires is 5–50 nm. The number of silver nanowires can be adjusted according to the concentration of the preparation solution. The parallel nanowire structure constructed by two silver nanowires reduces the surface plasmon transmission loss compared to a single silver nanowire.

[0007] Preferably, the parallel spacing or gap between the silver nanowire pairs is 10–20 nm.

[0008] Preferably, the length and diameter of the two silver nanowires in the silver nanowire pair are similar.

[0009] Preferably, the substrate includes: a SiO2 / Si substrate, a conventional silicon substrate, or a glass substrate.

[0010] This invention also discloses a method for reducing transmission loss based on parallel silver nanowires. The method is used to prepare the aforementioned structure for reducing transmission loss based on parallel silver nanowires, and includes the following steps:

[0011] Step 1: Prepare large-size silver nanowires;

[0012] Step 2: Using micromanipulation methods, the single silver nanowires on the substrate prepared in Step 1 are precisely moved to construct a parallel silver nanowire structure.

[0013] Step 3: Excite parallel silver nanowires to generate SPPs using fiber coupling and measure the transmission loss.

[0014] Preferably, in step 1, the preparation of large-size silver nanowires includes the following steps:

[0015] Step 1-1: Dissolve silver nitrate and PVP separately in ethylene glycol and stir until the reaction is complete and a clear, transparent liquid is obtained;

[0016] Step 1-2: Pour ethylene glycol solution into a three-necked flask and heat it. Use a syringe to draw up the two precursor solutions prepared in step 1-1 and inject them into the three-necked flask at a uniform rate. Stop the reaction when the solution turns milky white. Take a small amount of the solution and inject it into the three-necked flask. Repeat the above reaction process twice to prepare large-size nanowires.

[0017] Steps 1-3: After the reaction solution from Step 1-2 has cooled, wash the solution twice with acetone and anhydrous ethanol respectively to obtain large-sized silver nanowires.

[0018] More preferably, in step 1-1, each 10 ml of ethylene glycol corresponds to 0.25 g of AgNO3 and 0.20 g of PVP, and the stirring time is 50-80 minutes;

[0019] In steps 1-2: the heating temperature is 150-180℃, the optimal temperature is 165℃, and the reaction time is 40-60 minutes.

[0020] Preferably, in step 2, the micro-manipulation method includes the following steps:

[0021] Step 2-1: Fabrication of the fiber taper structure;

[0022] Step 2-2: Fix the fiber optic cone structure obtained in Step 2-1 using a three-dimensional adjustment frame and form a certain tilt angle with the SiO2 / Si substrate or ordinary silicon substrate. Disperse the silver nanowire solution on the SiO2 / Si substrate and place it on a rotating displacement stage. Under a microscope, select two suitable adjacent single silver nanowires with appropriate size and orientation (size can be determined by color). Adjust the position of the fiber optic cone and slowly push the two single silver nanowires to form a parallel silver nanowire structure. The angle adjustment of the silver nanowires and the fiber optic cone can be completed using the rotating displacement stage at the bottom. The optimal gap between the two silver nanowires is 10–20 nm.

[0023] More preferably, in step 2-1, the tip diameter of the fiber taper is 0.5 to 3 μm.

[0024] More preferably, the three-dimensional adjustment frame is a support frame that is adjustable in the X, Y, and Z directions to fix the rear of the fiber optic cone. The three-dimensional adjustment frame is provided with three studs with rotation axes parallel to the X, Y, and Z directions respectively. The rotation of the studs drives the three-dimensional adjustment frame to generate corresponding micro-displacements in the X, Y, and Z directions.

[0025] The rotary displacement stage is a rotatable support platform in the X and Y directions and in the horizontal plane for supporting and placing silver nanowires. The rotary displacement stage is equipped with two screws with rotation axes parallel to the X and Y directions respectively, and an angle adjustment screw with a rotation axis located in the horizontal plane. The rotation of the screws drives the rotary displacement stage to generate corresponding micro-displacements in the X and Y directions, and the rotation of the angle adjustment screw drives the rotary displacement stage to rotate in the horizontal plane.

[0026] The base of the three-dimensional adjustment frame, the base of the rotary displacement stage, and the base of the optical microscope are fixedly connected.

[0027] Preferably, the specific steps of step 3 are as follows:

[0028] Step 3-1: Fabrication of the fiber taper structure;

[0029] Step 3-2: Fix the optical fiber on the three-dimensional adjustment frame, and adjust the direction of the fiber taper along the axis of the silver nanowire under a microscope. Couple a laser into the optical fiber to excite SPPs on the parallel silver nanowire. Move the relative position of the fiber taper and the parallel silver nanowire structure, and record the intensity of the end-scattered light of the parallel silver nanowire structure at different positions to obtain the transmission loss of SPPs on the parallel silver nanowire. The laser power, excitation fiber taper, and parallel silver nanowire used in the experiment are all the same, and the angle between the excitation fiber taper and the silver nanowire is the same in all cases.

[0030] The beneficial effects of this invention are:

[0031] 1. This invention constructs a parallel metal nanowire structure, which enables the interaction between two metal nanowires to affect the field distribution of surface plasmons, thereby suppressing the radiation leakage of surface plasmons to the substrate during transmission and significantly reducing the transmission loss of surface plasmons.

[0032] 2. This invention first prepares silver nanowires, then constructs parallel silver nanowire composite structures using micromanipulation methods, and finally excites surface plasmons in the composite structure using near-field coupling to measure its transmission loss. This invention, on the one hand, allows for the assembly of parallel silver nanowire structures of arbitrary sizes using fiber-assisted manipulation, offering advantages such as simplicity, accuracy, and flexibility; on the other hand, it effectively maintains the optical field localization of surface plasmons, which is beneficial for constructing subwavelength-scale nanophotonic devices.

[0033] 3. The present invention achieves this by precisely adjusting the relative position and included angle of two single silver nanowires. Therefore, the assembly method of the present invention has the advantages of being simple, accurate and flexible in operation.

[0034] Parallel silver nanowire structures can be fabricated using microfabrication techniques. Silver nanowires prepared by this top-down etching method have a polycrystalline structure with a rough surface and significant transport loss of surface plasmons. Attached Figure Description

[0035] Figure 1 This is an electron microscope image of synthesized silver nanowires based on the structure and method for reducing transmission loss using parallel silver nanowires, as described in this invention.

[0036] Figure 2 This is a schematic diagram of the platform structure for assembling parallel silver nanowire structures using the micromanipulation method of this invention;

[0037] Figure 3 This is a schematic diagram of the process of assembling the tapered optical fiber into a parallel silver nanowire structure according to the present invention;

[0038] Figure 4 These are optical microscope images of the parallel silver nanowires and single nanowires of this invention;

[0039] Figure 5 This is a diagram illustrating the experimental process of exciting SPPs and measuring transmission loss using the fiber optic coupling method of this invention.

[0040] Figure 6 This is a graph showing the variation of surface plasmon scattering intensity at the ends of parallel silver nanowires and single nanowires of the present invention with transmission distance.

[0041] Figure 7 This is a graph showing the variation of transmission loss of parallel silver nanowires and single nanowires of the present invention with transmission distance. Detailed Implementation

[0042] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. 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 embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0043] refer to Figures 1-7 This embodiment utilizes a structure based on parallel silver nanowires to reduce transmission loss. At least one pair of parallel silver nanowires is disposed on a substrate. The diameter of the silver nanowires is 400–800 nm, the length is 10–20 μm, and the parallel spacing or gap between the pairs is 5–50 nm. The number of silver nanowires can be adjusted according to the concentration of the preparation solution. When two silver nanowires are placed parallel together, the transmission loss is reduced compared to a single silver nanowire. The length and diameter of the two silver nanowires in the pair are similar, and their positions are also close. The substrate comprises SiO2 / Si.

[0044] The method for reducing transmission loss based on parallel silver nanowire structures is as follows:

[0045] Step 1: Prepare large-size silver nanowires;

[0046] Step 2: Using micromanipulation methods, the single silver nanowires on the substrate prepared in Step 1 are precisely moved to construct a parallel silver nanowire structure.

[0047] Step 3: Excite parallel silver nanowires to generate SPPs using fiber coupling and measure the transmission loss.

[0048] Example

[0049] This embodiment describes a method for reducing transmission loss based on parallel silver nanowire structures. The method includes first preparing silver nanowires, then assembling the parallel silver nanowire structure using micromanipulation, and finally using fiber coupling to excite the parallel silver nanowires to generate SPPs and measuring the transmission loss.

[0050] In this embodiment, the diameter of the silver nanowire is 400-800 nm and the length is 10-20 μm. The size of the two silver nanowires can be arbitrarily selected.

[0051] In this embodiment, the method for preparing large-size silver nanowires includes the following steps:

[0052] Step A1: Dissolve silver nitrate and PVP separately in ethylene glycol and stir until the reaction is complete and a clear, transparent liquid is obtained;

[0053] Step A2: Pour ethylene glycol solution into a three-necked flask and heat it. Use a syringe to draw up the two precursor solutions from step A1 and inject the solutions into the three-necked flask at a uniform rate. Stop the reaction when a milky yellow flocculent substance appears in the solution.

[0054] Step A3: After the reaction solution cools, wash the solution multiple times with acetone and anhydrous ethanol to obtain large-sized silver nanowires.

[0055] In step A1, each 10 ml of ethylene glycol corresponds to 0.25 g of AgNO3 and 0.2 g of PVP, and the stirring time is 40 minutes.

[0056] In step A2, the heating temperature is 170℃ and the reaction time is 60 minutes.

[0057] In this embodiment, the method for assembling parallel silver nanowire structures using fiber-optic assisted manipulation includes the following steps:

[0058] Step B1: Fabricate the fiber taper structure;

[0059] Step B2: Fix the fiber cone structure from Step B1 with a three-dimensional adjustment frame and form a certain tilt angle with the SiO2 / Si substrate. Disperse the silver nanowire solution on the SiO2 / Si substrate and select two suitable adjacent single silver nanowires under a microscope. Adjust the position of the fiber cone and slowly push the two single silver nanowires to form a parallel silver nanowire structure.

[0060] In step B1, the tip diameter of the fiber taper is 2 μm.

[0061] In step B2, the position adjustment of the two silver nanowires can be accomplished using the rotary displacement stage at the bottom.

[0062] When mass production of photonic devices based on parallel nanowire structures is required, two silver nanowires can be placed parallel to each other in a groove using nanogrooving to achieve rapid batch fabrication of multiple pairs of silver nanowires. This enables low-loss light transmission in nanodevices and confines the light field to a relatively small lateral region.

[0063] In this embodiment, the fiber coupling method is used to excite parallel silver nanowires to generate SPPs and measure the transmission loss, including the following steps:

[0064] Step C1: Fabricate the fiber taper structure;

[0065] Step C2: Fix the optical fiber on the three-dimensional adjustment frame. Under the microscope, keep the direction of the fiber taper parallel to the silver nanowire. Couple a 633nm laser into the optical fiber to excite the SPPs on the parallel silver nanowire. Move the relative position of the fiber taper and the parallel silver nanowire structure, record the intensity of the scattered light at the end of the parallel silver nanowire structure, and calculate the transmission loss of the SPPs on the parallel silver nanowire.

[0066] In step C1, the tip diameter of the fiber taper is 1.5 μm.

[0067] In step C2, the laser power, excitation fiber taper, and parallel silver nanowires used in the experiment are all the same, and the contact method and angle between the excitation fiber taper and the silver nanowires are also the same.

[0068] Comparative Example

[0069] This comparative example utilizes a method of exciting single silver nanowires to generate SPPs using fiber coupling and measuring transmission loss, for comparing the transmission loss of different structures.

[0070] In this comparative example, the silver nanowires have a diameter of 600 nm and a length of 16 μm.

[0071] A method for generating SPPs by exciting a single silver nanowire using fiber coupling and measuring transmission loss includes the following steps:

[0072] Step D1: Fabricate the fiber taper structure;

[0073] Step D2: Fix the optical fiber on the three-dimensional adjustment frame. Keep the direction of the fiber taper parallel to the silver nanowire in the microscope. Couple a 633nm laser into the optical fiber to excite SPPs on a single silver nanowire. Move the relative position of the fiber taper and the single silver nanowire, record the intensity of scattered light at the end of the silver nanowire, and calculate the transmission loss of SPPs on the single silver nanowire.

[0074] In step D1, the tip diameter of the fiber taper is 1.5 μm.

[0075] In step D2, the laser power, excitation fiber taper, and single silver nanowire used in the experiment are all the same, and the angle between the excitation fiber taper and the silver nanowire is also the same.

[0076] The embodiments and comparative examples are described in detail below with reference to the accompanying drawings:

[0077] Figure 1 This is a scanning electron microscope image of synthesized silver nanowires, with a scale bar of 2 micrometers. The white areas represent the nanowires. The image shows that the nanowires prepared in the laboratory have a very smooth surface.

[0078] Figure 2 This is a schematic diagram of an apparatus for assembling parallel silver nanowire structures using optical fibers. The optical fiber is fixed on a three-dimensional adjustment frame to move the nanowires, and a rotary displacement stage is used to adjust the angle between the fiber taper and the two silver nanowires.

[0079] Figure 3 This is a schematic diagram illustrating the process of assembling parallel silver nanowire structures using tapered optical fibers. The individual nanowires are brought closer together by controlling the position of the tapered optical fibers. The dimensions of the two individual silver nanowires can be freely selected, offering excellent flexibility and operability.

[0080] Figure 4 These are optical microscope images of two structures, with a scale bar of 2 micrometers. The two nanowire branches of the parallel silver nanowire structure are approximately 500 nm in diameter and 13 μm in length, with similar dimensions and parallel orientation. The single silver nanowire used for comparison is approximately 600 nm in diameter and 16 μm in length.

[0081] Figure 5 This is an experimental procedure that uses fiber coupling to excite SPPs and measure transmission loss. A laser (633 nm) excites SPPs at different locations on a nanowire through a tapered optical fiber. The SPPs propagate along the nanowire and are eventually scattered as photons at the nanowire tip.

[0082] Figure 6The results are from transmission loss measurements of parallel silver nanowire structures using fiber coupling. As the transmission distance of SPPs increases, the intensity of scattered light at the silver nanowire ends decreases exponentially. The measured transmission length of the parallel silver nanowires is ~6.7 μm, while the transmission length of a single silver nanowire of similar diameter is...

[0083] ~6.0 μm. The transmission length of SPPs on the parallel silver nanowire structure is extended. Generally, the thicker the diameter of a single nanowire, the lower the corresponding loss. Although the parallel nanowires in this embodiment have a thinner diameter, the loss is still lower than that of a single thick nanowire. This illustrates the superiority of the parallel nanowire structure of the present invention.

[0084] Figure 7 This represents the variation of surface plasmon transmission loss with transmission distance for the two structures.

[0085] The transmission loss of parallel silver nanowires is 0.58 dB / μm, while that of a single silver nanowire of similar diameter reaches 0.77 dB / μm. Experimental results further demonstrate that the transmission loss of SPPs with parallel silver nanowire structures is significantly reduced.

[0086] In summary, this invention, by placing two parallel metal nanowires, fully utilizes the influence of the interaction between the metal nanowires on the surface plasmon field distribution, thereby suppressing radiation leakage of surface plasmons to the substrate during transmission, and significantly reducing the transmission loss of surface plasmons. Therefore, this invention has broad application prospects in constructing simple metal waveguide structures to reduce the transmission loss of surface plasmon photonic devices and improving their practical applications.

[0087] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications made to the above embodiments based on the technical essence of the present invention, including the use of other methods to prepare parallel metal nanowire structures or changes in the size of the nanowires, even if they differ from the size of the parallel nanowires in the present invention, shall fall within the protection scope of the present invention. Other equivalent changes and modifications shall still fall within the scope of the technical solution of the present invention.

Claims

1. A structure for reducing transmission loss based on parallel silver nanowires, characterized in that, The structure comprises at least one pair of parallel silver nanowires on a substrate, wherein the diameter of the silver nanowires is 400-800 nm, the length of the silver nanowires is 10-20 μm, and the parallel spacing or gap between the pairs of silver nanowires is 5-50 nm. The surface of the silver nanowires is smooth; The length and diameter of the two silver nanowires in the silver nanowire pair are similar. The substrate includes: SiO2 / Si substrate, ordinary silicon substrate or glass substrate.

2. A method for reducing transmission loss based on parallel silver nanowires, characterized in that, The method for reducing transmission loss using the structure described in claim 1 includes the following steps: Step 1: Prepare large-size silver nanowires; Step 2: Using micromanipulation methods, the single silver nanowires on the substrate prepared in Step 1 are precisely moved to construct a parallel silver nanowire structure. Step 3: Excite parallel silver nanowires to generate SPPs using fiber coupling and measure the transmission loss. In step 2, the micro-manipulation method includes the following steps: Step 2-1: Fabrication of the fiber taper structure; Step 2-2: Fix the fiber cone structure obtained in step 2-1 with a three-dimensional adjustment frame and form an angle with the substrate. Disperse the silver nanowire solution on the SiO2 / Si substrate or ordinary silicon substrate and place it on a rotating displacement stage. Under a microscope, select two adjacent single silver nanowires, adjust the position of the fiber cone and slowly push the two single silver nanowires to form a parallel silver nanowire structure.

3. The method for reducing transmission loss based on parallel silver nanowires according to claim 2, characterized in that, Step 1, the preparation of large-size silver nanowires, includes the following steps: Step 1-1: Dissolve silver nitrate and PVP separately in ethylene glycol and stir until the reaction is complete and a clear, transparent liquid is obtained; Step 1-2: Heat the ethylene glycol solution, take the solution prepared in step 1-1, and inject the solution into the ethylene glycol solution at a uniform rate. Stop the reaction when the solution shows milky yellow flocculent matter. Steps 1-3: After the reaction solution from Step 1-2 has cooled, wash the solution twice with acetone and anhydrous ethanol respectively to obtain large-sized silver nanowires.

4. The method for reducing transmission loss based on parallel silver nanowires according to claim 3, characterized in that, In step 1-1, each 10 ml of ethylene glycol corresponds to 0.25 g of AgNO3 and 0.20 g of PVP, and the stirring time is 50-80 minutes.

5. The method for reducing transmission loss based on parallel silver nanowires according to claim 2, characterized in that, In step 2-1, the tip diameter of the fiber taper is 0.5 to 3 μm.

6. The method for reducing transmission loss based on parallel silver nanowires according to claim 2, characterized in that, The three-dimensional adjustment frame is a support frame that can be adjusted in the X, Y, and Z directions to fix the rear of the fiber optic cone. The three-dimensional adjustment frame is equipped with three studs with rotation axes parallel to the X, Y, and Z directions respectively. The rotation of the studs drives the three-dimensional adjustment frame to generate corresponding micro-displacements in the X, Y, and Z directions. The rotary displacement stage is a rotatable support platform in the X and Y directions and in the horizontal plane for supporting and placing silver nanowires. The rotary displacement stage is equipped with two screws with rotation axes parallel to the X and Y directions respectively, and an angle adjustment screw with a rotation axis located in the horizontal plane. The rotation of the screws drives the rotary displacement stage to generate corresponding micro-displacements in the X and Y directions, and the rotation of the angle adjustment screw drives the rotary displacement stage to rotate in the horizontal plane. The base of the three-dimensional adjustment frame, the base of the rotary displacement stage, and the base of the optical microscope are fixedly connected.

7. The method for reducing transmission loss based on parallel silver nanowires according to claim 2, characterized in that, The specific steps of step 3 are as follows: Step 3-1: Fabrication of the fiber taper structure; Step 3-2: Couple the laser into the optical fiber to excite SPPs on the parallel silver nanowires. Keep the direction of the fiber taper close to parallel with the silver nanowire structure. Move the optical fiber precisely and adjust the relative position of the fiber taper and the parallel silver nanowire structure. Collect the scattered light from the end of the parallel silver nanowire structure. By comparing the intensity of the scattered light at different positions, calculate the transmission loss of SPPs on the parallel silver nanowires.

Images