A four-channel SPP transmitter and four-channel transmission method

Abstract

The present application relates to the technical field of surface plasmon polaritons, and specifically provides a four-channel SPP emitter and a four-channel emission method, wherein a first groove and a second groove are combined to obtain a coupling groove, the width of the first groove ranges from 0.2 to 0.4 microns, and the width of the second groove ranges from 0.9 to 1.1 microns; the coupling groove is irradiated by incident laser with a polarization angle of ±45°, a femtosecond SPP field is excited on the surface of the coupling groove, and the femtosecond SPP field is transmitted in four different directions by adjusting the polarization angle of the incident laser. In the case of irradiation of incident laser with different polarization angles, the femtosecond plasmon excited by the coupling groove can be transmitted in four different directions, four-channel emission is realized, and the carrying information capacity of a circuit module based on the four-channel SPP emitter is improved.

Description

Technical Field

[0001] This invention relates to the field of surface transport plasmon technology, specifically providing a four-channel SPP transmitter and a four-channel transmission method. Background Technology

[0002] High-end chips are core components of modern manufacturing. As chip technology enters the "post-Moore's Law era," the thermal and signal delay issues associated with electronic device interconnection have become insurmountable technological hurdles, severely limiting the achievement of higher integration and faster information processing capabilities in electronic chips. Compared to electronic chips, photonic chips possess unimaginable data-carrying capacity and can offer new solutions to the insurmountable thermal and signal processing speed improvement problems inherent in electronic devices. However, the interconnection of electronic and photonic devices within a chip faces the obstacle of the significant size difference between the two components. Due to the diffraction limit, the size of photonic devices is often at least one to two orders of magnitude larger than that of nanoscale electronic devices. This significant size mismatch between electronic and photonic components poses a major challenge to achieving interconnection between these technologies.

[0003] Surface-transmitted plasmons (SPPs) possess unique properties, including subwavelength localization and bandwidths approximately three orders of magnitude higher than those typically found in electronic devices. This allows SPP-based functional devices to replace traditional photonic devices, enabling synergy with nanoelectronic chips and bridging the size gap between nanoscale electronics and microscale photonics. SPP devices combine the advantages of both electronics and photonics: the ultra-small size of electronics and the ultra-high operating speed of photonics. Therefore, SPP functional devices offer a solution for building high-end chips in the post-Moore's Law era. In particular, ultrafast plasmons with broadband femtosecond optical excitation, used as information carriers, significantly increase information transmission rates, raising signal transmission rates from MHz to GHz in traditional electronics to THz and even PHz levels. Therefore, ultra-wideband femtosecond SPP device technology is an essential technology for future THz and even PHz ultra-high-speed communication devices, and will be of paramount importance to high-end chips in the post-Moore's Law era, characterized by high integration, high transmission rates, ultrafast computing speeds, and ultra-wideband performance.

[0004] Currently, various functional components based on plasmonic poles (SPPs) have been gradually developed, such as waveguides, nanocavities, switches, beam splitters, multiplexers, and filters based on the plasmonic effect. Among these SPP-based functional devices, achieving active control of the SPP field transmission direction is a crucial step in the design of various plasmonic functional components, and controlling the SPP field transmission direction has significant application value in optical logic circuits and optical communication systems. Therefore, achieving active control of multiple transmission directions of plasmons is of great research significance to the entire field of plasmonic devices.

[0005] In recent years, many researchers have focused on controlling the propagation direction of the SPP field. By adjusting the geometric parameters of the coupling structure, the propagation direction of the SPP field can be passively manipulated. While this passive manipulation method can control the SPP field propagation direction, it is highly dependent on the parameters of the coupling structure, difficult to fabricate, and the large structure size is not conducive to integration in plasmonic circuits. More importantly, this method cannot meet the more varied needs and integration of more functions in practical applications. As a leading candidate for engineering manipulation of the SPP propagation direction in plasmonic nanocircuits, the excitation beam polarization control scheme can achieve asymmetric momentum matching conditions between the incident light and the SPP in various femtosecond SPP coupling structures, thereby achieving the goal of controlling the SPP field propagation direction. Compared to the passive manipulation method that designs the coupling structure parameters, the active dynamic manipulation method that adjusts the polarization state of the incident laser to control the SPP field propagation direction has advantages such as simple operation and high flexibility. However, existing active dynamic control methods can only perform dual-channel control of the SPP field in the left-right or up-down transmission directions, and have not yet achieved active control of the SPP field in more transmission directions. The SPP multi-directional transmitter has immeasurable value for future practical applications. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a four-channel SPP emitter and, in conjunction with it, a specific four-channel emission method. By combining grooves of different sizes to obtain a coupling groove, and by changing the polarization angle of the incident laser illuminating the coupling groove, four-channel emission of femtosecond transmission plasmons excited by the coupling groove is achieved.

[0007] The four-channel SPP transmitter provided by the present invention includes: a metal film and a coupling groove disposed on the metal film;

[0008] The coupling groove includes a first groove and a second groove connected along the length direction. The width of the first groove ranges from 0.2 to 0.4 micrometers, and the width of the second groove ranges from 0.9 to 1.1 micrometers.

[0009] Preferably, the length of both the first groove and the second groove is 20 micrometers.

[0010] Preferably, the metal film is a silver nanofilm with a thickness of 100 nanometers.

[0011] Preferably, the substrate and the Ti adhesion layer are disposed below the metal film and between the substrate and the metal film.

[0012] A four-channel transmission method includes the following steps:

[0013] S1: Prepare a metal film on the substrate;

[0014] S2: Etch coupling grooves on a metal film, wherein the coupling grooves include a first groove and a second groove connected along the length direction, the width of the first groove is in the range of 0.2-0.4 micrometers, and the width of the second groove is in the range of 0.9-1.1 micrometers;

[0015] S3: The coupling groove is irradiated by incident lasers with different polarization angles. The coupling groove excites a femtosecond SPP field. By adjusting the polarization angle of the incident laser, the femtosecond SPP field is controlled to propagate in four different directions.

[0016] Preferably, the coupling groove is irradiated with an incident laser with a polarization angle of 45°, and the femtosecond SPP field excited by the first groove propagates along the lower side of the first groove, while the femtosecond SPP field excited by the second groove propagates along the upper side of the second groove; or the coupling groove is irradiated with an incident laser with a polarization angle of -45°, and the femtosecond SPP field excited by the first groove propagates along the upper side of the first groove, while the femtosecond SPP field excited by the second groove propagates along the lower side of the second groove.

[0017] Preferably, in S1: the substrate is a silicon substrate, and the metal film is a silver nanofilm; a silver nanofilm with a thickness of 100 nanometers is prepared on the silicon substrate by magnetron sputtering, and a 3-nanometer Ti adhesion layer is deposited between the silicon substrate and the silver nanofilm.

[0018] Preferably, the root mean square value of the particle size on the silver nanofilm is less than 5 nanometers.

[0019] Preferably, the incident laser is a femtosecond laser.

[0020] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0021] This invention solves the problem of dual-channel control of femtosecond SPP fields, which can only propagate in the left-right or up-down directions. By coupling first and second grooves of different sizes, a coupling groove is obtained. Under incident laser irradiation at different polarization angles, the femtosecond plasmons excited by the coupling groove can propagate in four different directions, realizing four-channel emission. This improves the information carrying capacity of the circuit module based on the four-channel SPP transmitter and has excellent application prospects. Attached Figure Description

[0022] Figure 1 This is a diagram of an experimental setup for a four-channel SPP transmitter according to an embodiment of the present invention;

[0023] Figure 2 This is a flowchart of a four-channel transmission method provided according to an embodiment of the present invention;

[0024] Figure 3 The image is a photoemission electron micrograph obtained when an incident laser with a polarization angle of ±45° irradiates an independent first groove, according to an embodiment of the present invention.

[0025] Figure 4 The image is a photoemission electron micrograph obtained when an incident laser with a polarization angle of ±45° irradiates an independent second groove, according to an embodiment of the present invention.

[0026] Figure 5 The image is a near-field distribution image obtained when an incident laser with a polarization angle of ±45° is irradiated by an independent first groove using FDTD simulation according to an embodiment of the present invention.

[0027] Figure 6 The image is a near-field distribution image obtained when an incident laser with a polarization angle of ±45° is irradiated by an independent second groove using FDTD simulation, according to an embodiment of the present invention.

[0028] Figure 7 These are images showing the results of a four-channel emission verification experiment using a coupling groove provided in an embodiment of the present invention.

[0029] Figure 8 The image shows the results of an experiment verifying the physical mechanism of plasmonic four-channel emission through a coupling groove according to an embodiment of the present invention.

[0030] The reference numerals in the figures include:

[0031] 1. Silicon substrate; 2. Silver nanofilm; 3. First groove; 4. Second groove. Detailed Implementation

[0032] In the following description, embodiments of the invention will be described with reference to the accompanying drawings. In the description below, the same modules are denoted by the same reference numerals. Where the same reference numerals are used, their names and functions are also the same. Therefore, their detailed description will not be repeated.

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0034] like Figure 1 The four-channel SPP emitter provided in this embodiment of the invention mainly includes a substrate, a metal film, and a coupling groove disposed on the metal film. The substrate is made of silicon and is described as silicon substrate 1 below. The metal film is made of silver and is described as silver nanofilm 2 below. The thickness of silver nanofilm 2 is 100 nanometers. Silicon substrate 1 is disposed below silver nanofilm 2, and a Ti adhesion layer is disposed between silicon substrate 1 and silver nanofilm 2. The thickness of Ti adhesion layer is 3 nanometers.

[0035] The coupling groove is composed of a first groove 3 and a second groove 4. The length of both the first groove 3 and the second groove 4 is 20 micrometers. The width of the first groove 3 ranges from 0.2 to 0.4 micrometers, and the width of the second groove ranges from 0.9 to 1.1 micrometers. The first groove 3 and the second groove 4 are connected along the length direction.

[0036] like Figure 2 As shown, based on the aforementioned four-channel SPP transmitter, this embodiment of the invention also provides a four-channel transmission method, and verifies the four-channel transmission of the four-channel SPP transmitter through PEEM experimental imaging and FDTD simulation. The specific steps are as follows:

[0037] S1: A silicon substrate 1 is provided, and a silver nanofilm 2 with a thickness of approximately 100 nanometers is prepared on the silicon substrate 1 by magnetron sputtering. During the preparation of the silver nanofilm 2 by magnetron sputtering, the presence of surface stress leads to the formation of irregularly sized and shaped silver nanoparticles on the surface of the silver nanofilm 2. These silver nanoparticles form femtosecond localized surface plasmon polariton (SPP) hotspots under near-infrared to near-ultraviolet femtosecond laser irradiation. These hotspots cause PEEM detector saturation, preventing the display of relatively weak femtosecond SPP signals, thus severely affecting PEEM's near-field characterization capability for transported surface plasmons. To avoid the formation of localized hotspots in the excitation field, it is necessary to control the particle size on the silver nanofilm 2, ensuring that the root mean square (RMS) value of the particle size is less than 5 nanometers. Therefore, it is necessary to constrain the environmental conditions during the preparation of the silver nanofilm 2. Specifically, during the preparation of the silver nanofilm 2, a good gas pressure needs to be maintained in the vacuum chamber, with a pressure better than 10. -6 Pa, and appropriately reduce the sputtering rate.

[0038] To ensure the accuracy of subsequent verification experiments, the silver nanofilm 2 finally prepared and used in the subsequent verification experiments in this embodiment of the invention has high flatness, the root mean square value of its surface particle size is between 2 and 3 nanometers, and a 3-nanometer Ti adhesion layer is deposited between the silicon substrate 1 and the silver nanofilm 2.

[0039] S2: Coupling grooves are etched on the silver nanofilm 2 prepared in S1 using focused ion beam lithography. The coupling grooves are composed of a first groove 3 and a second groove 4. The size of the first groove 3 is 0.2 μm × 20 μm, and the size of the second groove 4 is 1 μm × 20 μm.

[0040] S3: By irradiating the coupling groove with incident lasers at different polarization angles, a femtosecond SPP field is excited in the coupling groove. By adjusting the polarization angle of the incident laser, the propagation of the femtosecond SPP field in four different directions is controlled. Combined with... Figure 1 The experimental setup shown was used to conduct experiments and simulations for the specific dimensions of the coupling groove and the polarization angle of the incident laser, and the analysis is as follows:

[0041] First, it should be clarified that in the experiments and simulations below, femtosecond lasers are used as the incident lasers, with an incident angle of 65°. The projection of the incident laser onto the silver nanofilm 2 is perpendicular to the major axis of the first groove 3 and / or the second groove 4, and excites a femtosecond SPP field. The k in the experimental and simulation images below... S k represents the wave vector of the femtosecond SPP field. L This represents the wave vector projected onto the surface of the silver nanofilm 2 by the incident laser.

[0042] Furthermore, it is important to note that due to the strong local surface plasmon resonance, extremely bright hot spots appear at the edges and corners of the groove coupling under femtosecond laser illumination. These hot spots can easily cause saturation of the charge-coupled element, affecting the observation of the relatively weak SPP field. Therefore, to clearly demonstrate the propagation of the SPP field, the groove coupling structure is removed from the field of view of the photoelectron emission microscope. For example, Figure 3 The black dashed box on the right side indicates the location of the groove coupling structure.

[0043] Experimental and simulation analyses were conducted on the width range of the first groove 3 and the second groove 4. Specifically, the polarization angle of the incident laser was selected as -45° / 45°, the length of the groove structure was selected as 20 micrometers, and the width was selected as 0.2 micrometers.

[0044] The groove structure was irradiated with a -45° polarized incident laser, which excited a femtosecond SPP field. Imaging observation was then performed using a plate electron microscope (PEEM) to obtain... Figure 3 In diagram (a), it can be observed that when the polarization angle of the incident laser is -45°, the interaction between the incident laser and its induced femtosecond SPP forms an interference pattern parallel to the long axis of the groove structure, with the interference signal mainly concentrated on the upper side of the groove structure. By irradiating the groove structure with a 45° polarized incident laser, a femtosecond SPP field is excited within the groove structure. Imaging observation using an electron microscope yields the following results: Figure 3 In (b), it can be seen that when the polarization angle of the incident laser is 45°, the interaction between the incident laser and the femtosecond SPP induced by it forms an interference pattern parallel to the long axis of the groove structure 3, and the interference signal is mainly concentrated on the lower side of the groove structure.

[0045] The experimental results above show that by adjusting the polarization angle of the incident laser, the femtosecond SPP field excited in the groove structure can be transmitted along the upper or lower side of the groove structure, thereby realizing spatial manipulation of the transmission direction of the femtosecond SPP field.

[0046] Furthermore, the relationship between the dimensions of the groove structure and the propagation direction of the excited femtosecond SPP field was investigated experimentally. The length of the groove structure remained at 20 micrometers, while its width was modulated to 0.3 micrometers. The groove structure with adjusted width was irradiated with the same -45° / 45° polarized incident laser, and imaging observation was performed using an electron microscope to obtain the following results: Figure 3The images shown in (c) and (d) reveal that when the polarization angle of the incident laser is -45°, the incident laser interacts with its induced femtosecond SPP to form an interference pattern, with the interference signal mainly concentrated on the upper side of the groove structure; while when the polarization angle of the incident laser is 45°, the incident laser interacts with its induced femtosecond SPP to form an interference pattern, with the interference signal mainly concentrated on the lower side of the groove structure.

[0047] The length of the groove structure was kept at 20 micrometers, while its width was modulated to 0.4 micrometers. The adjusted groove structure was then irradiated with the same -45° / 45° polarized incident laser, and observed using an electron microscope to obtain... Figure 3 The images shown in (e) and (f) reveal that when the polarization angle of the incident laser is -45°, the incident laser interacts with its induced femtosecond SPP to form an interference pattern, and the interference signal is still mainly concentrated on the upper side of the groove structure; while when the polarization angle of the incident laser is 45°, the incident laser interacts with its induced femtosecond SPP to form an interference pattern, and the interference signal is still mainly concentrated on the lower side of the groove structure.

[0048] The experimental results show that when the length of the groove structure is 20 μm, the width ranges from 0.2 μm to 0.4 μm, and the polarization angle of the incident laser is -45°, the femtosecond SPP field formed by the incident laser irradiating the groove structure is excited along the upper side of the groove structure, while when the polarization angle of the incident laser is 45°, the femtosecond SPP field formed by the incident laser pulse irradiating the groove structure is excited along the lower side of the groove structure.

[0049] Furthermore, the dimensions of the groove structure were further adjusted to investigate the relationship between the groove structure's dimensions and the propagation direction of the excited femtosecond SPP field when irradiated by incident laser. The length of the groove structure remained at 20 micrometers, while its width was increased to 0.9 micrometers. At this point, the groove structure was irradiated with the same -45° polarized incident laser, and imaging observation was performed using an electron microscope to obtain the following results: Figure 4 Image (a) shows that the propagation direction of the femtosecond SPP excited by the groove structure is mainly along the lower side of the groove; while when the groove structure is irradiated with an incident laser with 45° polarization, the propagation direction of the femtosecond SPP excited by the groove structure is mainly along the upper side of the groove. This experimental result is completely opposite to the experimental results for smaller grooves with widths of 0.2-0.4 micrometers. To further verify the above experimental results, the length of the groove structure was kept at 20 micrometers, and the width was increased to 1.0 and 1.1 micrometers, and the same experiment was performed twice more. The experimental results are as follows: Figure 4As shown in Figure (cf). From the figure, it can be seen that, firstly, the experimental results were repeatedly verified through multiple sets of experiments, proving that the experimental results for the larger groove structure are indeed completely opposite to those for the smaller groove with a width of 0.2-0.4 micrometers; secondly, even when the size of the groove structure is further increased, the experimental results obtained are still the same as those when the groove width is 0.9 micrometers, that is: when the incident laser is polarized at -45°, the femtosecond SPP signal excited by the large groove structure is mainly concentrated on the lower side, and when the incident laser is polarized at 45°, the femtosecond SPP signal excited by the large groove structure is mainly concentrated on the upper side.

[0050] The experimental results above show that adjusting the polarization of the incident laser and the size of the groove structure can change the propagation direction of the SPP field excited by the groove structure.

[0051] Furthermore, to solidify the above experimental conclusions, the same parameters as in the experiment were selected, and the experiment was simulated and reproduced using FDTD, and the experimental results were verified.

[0052] like Figure 5 As shown, FDTD simulations used incident laser pulses with -45° / 45° polarization to irradiate small grooves (uniform length 20 μm, widths of 0.2 μm, 0.3 μm, and 0.4 μm, respectively), resulting in... Figure 5 The near-field distribution |E is shown in (af). Z | 2 .

[0053] Existing photoelectron emission experiments show that, under oblique incidence excitation conditions, the measured multiphoton signal is mainly generated by the E photon emission near the electric field. Z Dominated by weight. From Figure 5 As can be seen from (af), when the width of the groove structure is 0.2μm-0.4μm and the length remains constant at 20μm, the femtosecond SPP field excited by the -45° polarized incident laser is mainly concentrated on the upper side of the groove. When the incident laser polarization is adjusted to 45° to irradiate the groove coupling structure, the femtosecond SPP field excited by the groove structure is mainly concentrated on the lower side of the groove. This simulation result is consistent with the propagation direction of the SPP field excited when imaging a smaller groove structure using PEEM, showing good agreement between the FDTD simulation and the PEEM experiment.

[0054] Building upon this, further simulations using FDTD were conducted to determine when a large groove (uniform length 20 μm, widths of 0.9 μm, 1.0 μm, and 1.1 μm, respectively) was irradiated by an incident laser with -45° / 45° polarization. Figure 6 The near-field distribution |E is shown in (af). Z | 2 The simulated parameters are consistent with the experimental parameters.

[0055] according to Figure 6 The FDTD simulation results shown in (af) reveal that increasing the width of the groove structure alters the propagation direction of the femtosecond SPP field excited by incident lasers of different polarizations compared to smaller grooves. Specifically, when the groove structure is irradiated with a -45° polarized incident laser, the excited femtosecond SPP field is mainly concentrated on the lower side of the groove. Adjusting the incident laser pulse polarization to 45° to irradiate the groove structure, the excited femtosecond SPP field is mainly concentrated on the upper side. This simulation result is consistent with the propagation direction of the SPP field excited when imaging a larger groove structure using PEEM. The FDTD simulation and PEEM experiment show good consistency, fully confirming the accuracy of the experimental results.

[0056] Based on the experimental and simulation results above, the following conclusions were obtained and verified: When incident laser pulses with different polarizations (±45°) irradiate groove-coupled structures of different sizes, the propagation direction of the excited SPP field is different. Specifically, when the incident laser pulse is 45° polarized, when it irradiates a smaller groove structure (length: 20 μm, width 0.2 μm-0.4 μm), the excited femtosecond SPP field mainly propagates along the lower side of the groove structure, while when it irradiates a larger groove structure (length: 20 μm, width 0.9 μm-1.1 μm), the excited femtosecond SPP field mainly propagates along the upper side of the groove structure. When the incident laser is -45° polarized, the propagation direction of the femtosecond SPP field excited by the groove structure is completely opposite to that when it is polarized at 45°. That is, when it is irradiated by a smaller groove structure (length: 20 μm, width 0.2 μm-0.4 μm), the femtosecond SPP field excited by it mainly propagates along the upper side of the groove structure, while when it is irradiated by a larger groove structure (length: 20 μm, width 0.9 μm-1.1 μm), the femtosecond SPP field excited by it mainly propagates along the lower side of the groove structure.

[0057] Based on the above experimental conclusions, a groove with a length of 20 micrometers and a width of 0.2 micrometers was selected, denoted as the first groove 3; a groove with a length of 20 micrometers and a width of 1.1 micrometers was selected, denoted as the second groove 4. The first groove 3 and the second groove 4 were combined along the long axis of the grooves, and the resulting new groove structure was denoted as the coupling groove. This coupling groove is the main structure of the four-channel SPP transmitter. Four-channel transmission is achieved through the coupling groove. The four-channel transmission performance of the coupling groove was verified through the following experiments and simulations, obtaining the following results: Figure 7 The image shown is a photoemission electron micrograph, where W1 represents the width of the first groove 3 and W2 represents the width of the second groove 4.

[0058] First, the coupling groove is irradiated with a 45° polarized incident laser to obtain, as shown in the figure. Figure 7 The photoemission electron microscopy image shown in (a) shows that when the polarization of the incident laser is 45°, the propagation direction of the femtosecond SPP field excited by the second groove 4 in the coupling groove is as follows. Figure 7 As shown by the upper dashed line in (a), it is mainly concentrated on the upper side of the second groove 4. Meanwhile, the propagation direction of the femtosecond SPP field excited by the first groove 3 in the coupling groove is as follows... Figure 7 As shown by the dashed line at the bottom in (a), it is mainly concentrated on the lower side of the first groove 3.

[0059] Secondly, the polarization angle of the incident laser was adjusted to -45°, and the above experiment was repeated to obtain the following results. Figure 7 The photoemission electron microscopy image shown in (b) shows that the obtained results are consistent with... Figure 7 The results shown in (a) are the opposite; the propagation directions of the femtosecond SPP fields excited by the first groove 3 and the second groove 4 both change. Specifically, when the polarization of the incident laser is -45°, the propagation direction of the femtosecond SPP field excited by the second groove 4 in the coupling groove is as follows: Figure 7 As shown by the upper dashed line in (b), it is mainly concentrated on the lower side of the second groove 4. Meanwhile, the propagation direction of the femtosecond SPP field excited by the first groove 3 in the coupling groove is as follows... Figure 7 As shown by the lower dashed line in (b), it is mainly concentrated on the upper side of the first groove 3.

[0060] The above experimental results show that by adjusting the polarization angle of the incident laser pulse, the transmission direction of the femtosecond SPP field excited on the coupling groove can be switched in four different directions, thus realizing the functionality of the coupling groove as a four-channel SPP transmitter.

[0061] Furthermore, using the same parameters as the experiment, the above experiment was reconstructed using FDTD simulation, and the experimental results were verified. When the incident laser was -45° / 45° polarized and irradiated the coupling groove using FDTD simulation, the following results were obtained: Figure 7 The near-field distributions |E shown in (c) and (d) Z | 2 The simulation parameters, such as the coupling groove and the incident laser, are consistent with those used in the above experiments. For example... Figure 7 Figure (c) shows the near-field distribution |E| obtained by FDTD simulation of incident laser polarization at 45° irradiation of the coupling groove. Z | 2As can be observed, when the 45° polarized incident laser irradiates the coupling groove, the propagation direction of the femtosecond SPP field excited by the second groove 4 is shown by the upper dashed arrow in the figure, mainly concentrated on the upper side of the second groove 4. Conversely, the propagation direction of the femtosecond SPP field excited by the first groove 3 is shown by the lower dashed arrow in the figure, mainly concentrated on the lower side of the second groove 4. This simulation result is consistent with the experimental phenomena obtained in the PEEM experiment. Adjusting the polarization angle of the incident laser to -45° and irradiating the coupling groove yields the following simulation results: Figure 7 As shown in Figure (d), it can be observed that, compared to the result when the coupling groove is irradiated by a 45° polarized incident laser, the propagation direction of the femtosecond SPP field excited by the first groove 3 and the second groove 4 in the coupling groove has changed. Specifically, the propagation direction of the femtosecond SPP field excited by the second groove 4 is shown by the upper dashed arrow in the figure, mainly concentrated on the lower side of the second groove 4, while the propagation direction of the femtosecond SPP field excited by the first groove 3 is shown by the lower dashed arrow in the figure, mainly concentrated on the upper side of the first groove 3. The above simulation results show that adjusting the polarization of the incident laser can control the propagation of the femtosecond SPP field excited by the coupling groove in four different directions, and the high consistency between the FDTD simulation results and the experimental results fully confirms the functionality of the coupling as a four-channel SPP emitter.

[0062] In summary, the embodiments of the present invention provide a coupling groove formed by the combination of the first groove 3 and the second groove 4 to achieve four-channel emission, and this has been verified.

[0063] To explain the fundamental principle of four-channel emission achieved by the coupling groove, the physical mechanism of four-channel emission achieved by the coupling groove is further analyzed from the perspective of the destructive and constructive interference angles between the SPP modes excited by incident lasers with different polarization directions. The specific process is as follows:

[0064] Using FDTD simulations, the first groove 3 (20 μm in length and 0.2 μm in width) was irradiated with incident lasers of different polarizations to obtain, as shown... Figure 8 The pattern distribution E shown in (a) and (b) Z ,in, Figure 8 In the middle (a), it indicates that the incident laser is P-polarized. Figure 8 In Figure (b), the incident laser is S-polarized. It can be observed that when the incident laser is P-polarized, the SPP near-field exhibits a symmetrical mode along the central axis of the first groove 3; while when the incident laser pulse is S-polarized, the SPP near-field exhibits an anti-symmetrical mode along the central axis of the first groove 3, and the intensities of the femtosecond SPP fields excited on both sides of the first groove 3 are the same. Since any polarization state can be decomposed into a superposition of S-polarized and P-polarized states, taking 45° linear polarization as an example, it can be decomposed into a superposition of P and S polarizations with an initial phase of θ(0,0).

[0065] Furthermore, the reason for the difference in the propagation direction of the femtosecond SPP field excited when a 45° polarized incident laser irradiates the first groove 3 and the second groove 4 is analyzed from the perspective of field superposition. Specifically, FDTD simulation of a 45° polarized incident laser irradiating the first groove 3 (20 μm in length and 0.2 μm in width) is first used to obtain the following results: Figure 8 The temporal evolution of the SPP near-field at the two symmetrical positions P1 and P2 shown in (c) and (d) reveals that the temporal evolution of the near-electric field at position P1 is approximately the same for the SPP modes excited by P-polarized and S-polarized incident lasers, while the phase at position P2 is nearly out of phase. This indicates that when the two SPP modes are superimposed, constructive interference occurs on the lower side of the first groove 3, and destructive interference occurs on the upper side of the first groove 3, resulting in the femtosecond SPP field excited by the 45° polarized incident laser irradiating the first groove 3 being mainly concentrated on the lower side of the first groove 3.

[0066] Similarly, by using FDTD to simulate 45° polarized incident laser irradiation of the second groove 4 (20 μm in length and 1.0 μm in width), the following results were obtained: Figure 8 The temporal evolution of the SPP near-field at the two symmetrical positions P1 and P2 shown in (e) and (f) reveals that the near-field temporal evolution of the SPP modes excited by P-polarized and S-polarized incident lasers is nearly out of phase at position P1, while the phases at position P2 are approximately the same. This indicates that when the two SPP modes are superimposed, constructive interference occurs on the upper side of the second groove 4, and destructive interference occurs on the lower side of the first groove 3. Consequently, the femtosecond SPP field excited by the 45° polarized incident laser irradiating the second groove 4 is mainly concentrated on the lower side of the first groove 3.

[0067] In summary, it can be explained that when a coupling groove is irradiated by an incident laser of the same polarization, the femtosecond SPP fields excited by the first groove 3 and the second groove 4 will have different propagation directions. This is because the SPP modes excited by the incident laser are superimposed from the P and S polarization components, respectively. The constructive and destructive interferences of the first groove 3 and the second groove 4 occur at opposite positions. Therefore, the femtosecond SPP fields excited by the first groove 3 and the second groove 4 will be concentrated at different locations. Thus, by irradiating the coupling groove obtained by the combination of the first groove 3 and the second groove 4 with incident lasers of different polarization angles, the propagation of the excited femtosecond SPP fields in four different directions can be controlled by adjusting the polarization angle of the incident laser.

[0068] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention.

[0069] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A four-channel SPP transmitter, characterized in that, include: A metal film, and a coupling groove disposed on the metal film; The coupling groove includes a first groove and a second groove connected along the length direction. The width of the first groove ranges from 0.2 to 0.4 micrometers, and the width of the second groove ranges from 0.9 to 1.1 micrometers. The metal film is a silver nanofilm with a thickness of 100 nanometers. It also includes: a substrate and a Ti adhesion layer, wherein the substrate is disposed below the metal film and the Ti adhesion layer is disposed between the substrate and the metal film.

2. The four-channel SPP transmitter as described in claim 1, characterized in that, The length of both the first groove and the second groove is 20 micrometers.

3. A four-channel transmission method, characterized in that, Includes the following steps: S1: A metal film is prepared on a substrate, the substrate being a silicon substrate and the metal film being a silver nanofilm; a silver nanofilm with a thickness of 100 nanometers is prepared on the silicon substrate using magnetron sputtering, and a 3-nanometer Ti adhesion layer is deposited between the silicon substrate and the silver nanofilm. S2: Etching coupling grooves on the metal film, wherein the coupling grooves include a first groove and a second groove connected along the length direction, the width of the first groove is in the range of 0.2-0.4 micrometers, and the width of the second groove is in the range of 0.9-1.1 micrometers; S3: The coupling groove is irradiated with incident lasers at different polarization angles, and the coupling groove excites a femtosecond SPP field. By adjusting the polarization angle of the incident laser, the femtosecond SPP field is controlled to propagate in four different directions.

4. The four-channel transmission method as described in claim 3, characterized in that, When the coupling groove is irradiated with an incident laser with a polarization angle of 45°, the femtosecond SPP field excited by the first groove propagates along the lower side of the first groove, and the femtosecond SPP field excited by the second groove propagates along the upper side of the second groove; when the coupling groove is irradiated with an incident laser with a polarization angle of -45°, the femtosecond SPP field excited by the first groove propagates along the upper side of the first groove, and the femtosecond SPP field excited by the second groove propagates along the lower side of the second groove.

5. The four-channel transmission method as described in claim 3, characterized in that, The root mean square value of the particle size on the silver nanofilm is less than 5 nanometers.

6. The four-channel transmission method as described in claim 3, characterized in that, The incident laser is a femtosecond laser.

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