Device and method for modulating the polarization of two-dimensional crystal bandgap fluorescence

Abstract

The present invention discloses a device and method for modulating the polarization of two-dimensional crystal bandgap fluorescence. The device comprises: a highly conductive material substrate; an insulating layer formed on the highly conductive material substrate; a two-dimensional crystal monolayer formed on the insulating layer; a light-transmitting dielectric layer formed on the two-dimensional crystal monolayer; and a metal nano-metamaterial having a periodic unit structure formed on the light-transmitting dielectric layer. Based on the principle of metal surface plasmon resonance, the present invention utilizes the anisotropic resonant field of the metal nano-metamaterial to control the semiconductor fluorescence field, achieving polarized fluorescence and achieving polarization tunability. The device and method for modulating the polarization of two-dimensional crystal bandgap fluorescence effectively broaden the linear tunable range and temperature applicable range of the two-dimensional crystal bandgap fluorescence.

Description

Technical Field

[0001] The present invention belongs to the field of nano-photoelectronic technology, and in particular relates to a device and method for modulating the polarization of two-dimensional crystal bandgap fluorescence. Background Art

[0002] Polarity-tunable micro-nanolight sources offer unique advantages in information security, high-sensitivity sensing, structural analysis, and pathogen diagnosis. Recent developments in novel two-dimensional crystals offer broad direct bandgap selectivity, structural stability, optoelectronic tunability, and substrate diversity, providing excellent conditions for on-chip micro-nanolight sources. However, the random polarization of fluorescence at room temperature limits the application of micro-nanolight sources, necessitating polarization modulation of on-chip light sources.

[0003] The macroscopic optical path uses polarizers and polarizing prisms to modulate the polarization of light. Polarizers primarily consist of a polyvinyl alcohol (PVA) polarizing film laminated on its top and bottom surfaces with a transparent triacetyl cellulose protective film. The main components of the PVA polarizing film are polyvinyl alcohol (PVA) and iodine, and it is produced using a wet stretching process. The typical process involves first producing a thick, transparent PVA film by casting or melt extrusion. This film is then immersed in an iodine-containing compound solution for reaction, dyeing the film with iodine. Next, the PVA film is uniaxially stretched 3-5 times in a specific direction between rollers rotating at varying speeds. This aligns the PVA molecular bonds and simultaneously orients the embedded iodine molecules, imparting dichroism, absorbing light polarized in the same direction as the stretching and transmitting light perpendicular to the stretching direction. Because PVA polarizing film rapidly deforms, shrinks, relaxes, and degrades in warm environments, it also has low strength, is brittle, and is difficult to use and process. Therefore, a triacetyl cellulose protective film with high transmittance, excellent heat and temperature resistance, high strength, and optical isotropy is applied to its top and bottom surfaces. This increases the thickness of the polarizer and cannot be directly integrated into the photonic device. In addition, the polarizer can also be made of dichroic crystals, such as calcite, which are designed, cut, polished and assembled according to the unique aspect ratio and end angle requirements. Although the polarizer prepared by polarizing prism has the advantages of high extinction ratio, high transmittance and high damage threshold. However, its blocky crystal characteristics make its practicality and compatibility in micro-nano photonic systems very low. Therefore, whether in terms of material structure or processing technology, traditional polarization elements are not suitable for photonic chips.

[0004] Different from macroscopic optical elements, on-chip photonic device modulation has its own unique theoretical basis and working method. In terms of the modulation of two-dimensional crystal fluorescence polarization, predecessors have used temperature and magnetic field as two modulation methods for research. First, at low temperatures, linearly polarized fluorescence can be generated by utilizing the valley polarization effect of two-dimensional crystals. The valley polarization of two-dimensional crystals refers to the formation of two valleys (K) in the K space due to the breaking of the central symmetry of a single-layer crystal. + and K -These two valleys can be detected with circularly polarized light. When excited by external circularly polarized laser light, they emit circularly polarized fluorescence with corresponding properties. Because linearly polarized light is a coherent superposition of left- and right-handed light, when linearly polarized light is used to excite a two-dimensional crystal, the left- and right-handed components interact with the left and right valleys, respectively, causing the left and right valley electrons to simultaneously jump from their respective valence bands to the conduction bands, emitting left- and right-handed fluorescence. The coherent superposition of these two components forms linearly polarized fluorescence. This process requires a crucial condition: the decoherence time of the left and right valley excitons must be greater than the electron-hole recombination time. Conversely, if the left and right valley excitons decohere before electron-hole recombination occurs, only randomly polarized fluorescence will be obtained. Higher temperatures increase the intervalley scattering caused by phonon resonances and shorten the decoherence time, which is the primary cause of random polarization at room temperature. Lower temperatures reduce the intervalley scattering, increase the decoherence time, and improve the linear polarization of the fluorescence. Utilizing this principle, related work has achieved a fluorescence linearity of 35% at the ultra-low temperature of 30K. Secondly, in the absence of a magnetic field, the optical axis of linearly polarized fluorescence remains parallel to the optical axis of the excitation laser at low temperatures. However, when a magnetic field is applied perpendicular to the surface of the two-dimensional crystal, the polarization direction of the linearly polarized fluorescence is deflected by the valley Zeeman splitting effect, and the polarization degree drops to 16%. This shows that temperature and magnetic fields are feasible means of modulating the fluorescence polarization properties of two-dimensional crystals. However, both methods have their own drawbacks and limitations: first, the modulation of fluorescence polarization is weak; second, under extreme conditions, they are difficult to apply widely. Summary of the Invention

[0005] (1) Technical issues to be solved

[0006] To overcome the shortcomings and deficiencies of the above modulation methods, the present invention proposes a device and method for modulating the polarization of two-dimensional crystal bandgap fluorescence using anisotropic metamaterials to solve the problems of weak polarization modulation and temperature limitation.

[0007] (2) Technical solution

[0008] The present invention provides a device for modulating the polarization of two-dimensional crystal bandgap fluorescence, the structure comprising:

[0009] a highly conductive material substrate;

[0010] an insulating layer formed on the highly conductive material substrate;

[0011] a two-dimensional crystal monolayer formed on the insulating layer;

[0012] a light-transmitting medium layer formed on the two-dimensional crystal monolayer; and

[0013] A metal nano-metamaterial with a periodic unit structure is formed on the light-transmitting medium layer.

[0014] Wherein, the highly conductive material substrate is a highly doped silicon or metal substrate with a thickness of 500-750 μm; the highly conductive material plays a structural support role and reflects the fluorescence of the two-dimensional crystal monolayer;

[0015] Wherein, the insulating layer is SiO2 or Al2O3, and has a thickness of 270-310 nm; the insulating layer serves as a growth substrate for the two-dimensional crystal monolayer;

[0016] The two-dimensional crystal is a single-layer transition metal chalcogenide MX2, wherein M=Mo, W; X=S, Se, Te; the thickness of the two-dimensional crystal single layer is less than 1 nm; and the two-dimensional crystal single layer emits fluorescence under the excitation of pump light;

[0017] The light-transmitting dielectric layer is Al2O3 or SiO2, and has a thickness of 10-50 nm. The thickness of the light-transmitting dielectric layer affects the resonant transmission and absorption of the metal nano-metamaterial at the excitation field, further affecting the fluorescence intensity. The light-transmitting dielectric layer protects the two-dimensional crystal material from the influence of water, oxygen or impurity ions.

[0018] Wherein, the metal nano-metamaterial is a metal nanostructure such as gold, silver or aluminum, with a thickness of 30-100nm;

[0019] The metal nano-metamaterial with a periodic unit structure has a linear, V-shaped or N-shaped air gap structure; the angle between the V-shaped or N-shaped air gap structure and the horizontal direction is the air gap inclination angle θ.

[0020] Based on the above-mentioned metamaterial polarization modulation device, the present invention further provides a method for modulating the polarization of two-dimensional crystal bandgap fluorescence using the device, the method comprising:

[0021] According to the wavelength of the pump light, that is, the wavelength of the excitation field, the thickness of the light-transmitting medium layer is determined to achieve strong resonant transmission and absorption of the metamaterial at the excitation field;

[0022] determining a fluorescence wavelength according to the band gap width of the two-dimensional crystal monolayer, i.e., a monolayer transition metal chalcogenide;

[0023] Determine the period range of the metal nano-metamaterial unit structure based on the fluorescence wavelength;

[0024] By adjusting the air gap inclination angle θ within the metal nano-metamaterial unit structure, the resonant mode position is fine-tuned to obtain the maximum fluorescence polarization degree.

[0025] Among them, in the step of determining the period range of the metal nano-metamaterial according to the fluorescence wavelength, after the period is determined, it is ensured that the surface plasmon resonance mode of the metamaterial is located near the fluorescence wavelength, but not necessarily exactly at the fluorescence wavelength; in the step of adjusting the air gap inclination angle θ in the metamaterial unit structure, by adjusting the air gap inclination angle θ, the device can adjust the polarization degree of the two-dimensional crystal band gap fluorescence from high to low or from low to high.

[0026] (3) Beneficial effects

[0027] It can be seen from the above technical solutions that the device and method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal proposed in the present invention have the following beneficial effects:

[0028] (1) The present invention provides an apparatus and method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal. Metamaterials are used to modulate the polarization of the bandgap fluorescence of a two-dimensional crystal. Since the surface plasmon resonance of the metamaterial is the collective resonance behavior of light and electrons on the surface of the metamaterial, it is not affected by temperature. Therefore, the polarization modulation method proposed by the present invention effectively broadens the applicable temperature range.

[0029] (2) The present invention provides a device and method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal. By optimizing the structural design, the coupling degree between the metamaterial resonant mode and the two-dimensional crystal fluorescence is adjusted to generate fluorescence signals of different linearities, thereby widening the adjustable range of linearity.

[0030] (3) The present invention provides a device and method for modulating the polarization of bandgap fluorescence in a two-dimensional crystal. Due to the small size of the metamaterial, its freedom from the optical diffraction limit, and its suitability for on-chip fixed-point integration, the device's size is flexible and adjustable, making it suitable for on-chip integration and micro-nano light source modulation. The minimum adjustable area is determined by the metamaterial's structural unit and, at the scale of hundreds of nanometers squared, provides a device foundation for the development of chip-scale photonic devices, systems, and functions.

[0031] (4) The present invention provides an apparatus and method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal. During the preparation process, a light-transmitting medium layer prepared by an evaporation method isolates the two-dimensional crystal from the outside world, thereby reducing the influence of factors such as water and oxygen on the two-dimensional crystal and improving the life of the device.

[0032] (5) The present invention provides an apparatus and method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal, wherein the substrate material of the two-dimensional crystal has multiple selectivities and has good compatibility with silicon-based photonic platforms and micro-nano fabrication technologies. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the structure of a device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal according to an embodiment of the present invention.

[0034] Figure 2 FIG. 4 is a flowchart of the working process of a device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal according to an embodiment of the present invention.

[0035] Figure 3 for Figure 1 The test flow chart of the device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal is shown.

[0036] Figure 4A This is an optical imaging diagram of a WS2 single layer according to an embodiment of the present invention;

[0037] Figure 4B : is a fluorescence intensity diagram of a WS2 monolayer in the TE and TM directions according to one embodiment of the present invention;

[0038] Figure 4C Graph showing the variation of the fluorescence peak value of a WS2 single layer with the emission angle according to one embodiment of the present invention;

[0039] Figure 4D is a graph showing the variation of fluorescence linearity of a WS2 monolayer with fluorescence wavelength according to one embodiment of the present invention;

[0040] Figure 5A is a SEM image of a nanowire grid according to an embodiment of the present invention;

[0041] Figure 5B The fluorescence spectra in the TE and TM directions of the device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using a nanowire grid according to an embodiment of the present invention are shown;

[0042] Figure 5C This is a diagram showing the variation of fluorescence peak value with emission angle in a device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using a nanowire grid according to an embodiment of the present invention;

[0043] Figure 5D A graph showing the variation of fluorescence linearity with fluorescence wavelength in a device for modulating the polarization of two-dimensional crystal bandgap fluorescence using a nanowire grid according to an embodiment of the present invention;

[0044] Figure 6 A schematic diagram of a V-shaped nanograting surface structure according to an embodiment of the present invention;

[0045] Figure 7A is a SEM image of a V-shaped metal nanograting when θ=51° according to an embodiment of the present invention;

[0046] Figure 7B is a white light reflection spectrum of the V-shaped nanograting in the TE direction when θ=51° according to an embodiment of the present invention;

[0047] Figure 7CGraphs showing fluorescence spectra in the TE and TM directions of a device for modulating the polarization of fluorescence bandgap of a two-dimensional crystal using a V-shaped nanograting when θ=51° according to an embodiment of the present invention;

[0048] Figure 7D This is a graph showing the variation of the fluorescence peak value with the emission angle of the device for modulating the polarization of the two-dimensional crystal band gap fluorescence when θ=51° according to an embodiment of the present invention;

[0049] Figure 7E The curve of fluorescence linearity versus fluorescence wavelength for the device where the V-type nanograting modulates the polarization of the two-dimensional crystal band gap fluorescence when θ=51°;

[0050] Figure 8A is a SEM image of a V-shaped metal nanograting when θ=63° according to an embodiment of the present invention;

[0051] Figure 8B : is a white light reflection spectrum of the V-shaped nanograting in the TE direction when θ=63° according to an embodiment of the present invention;

[0052] Figure 8C Graphs showing fluorescence spectra in the TE and TM directions of a device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using a V-shaped nanograting when θ=63° according to an embodiment of the present invention;

[0053] Figure 8D This is a graph showing the variation of the fluorescence peak value with the emission angle of the device for modulating the polarization of the two-dimensional crystal band gap fluorescence when θ=63° according to an embodiment of the present invention;

[0054] Figure 8E A graph showing the variation of fluorescence linearity with fluorescence wavelength for a device for modulating the polarization of two-dimensional crystal bandgap fluorescence using a V-shaped nanograting when θ=63° according to an embodiment of the present invention;

[0055] Figure 9 Schematic diagram of the surface structure of an N-type nanogate according to an embodiment of the present invention;

[0056] Figure 10A is a SEM image of an N-type nanograting when θ=30° according to an embodiment of the present invention;

[0057] Figure 10B : is the white light reflection spectrum of the N-type nanograting in the TE direction when θ=30° according to an embodiment of the present invention;

[0058] Figure 10C The fluorescence spectra in the TE and TM directions of the device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using an N-type nanograting when θ=30° according to an embodiment of the present invention are shown;

[0059] Figure 10DThis is a graph showing the variation of the fluorescence peak value with the emission angle of the device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using an N-type nanograting when θ=30° according to an embodiment of the present invention;

[0060] Figure 10E This is a graph showing the variation of fluorescence linearity with fluorescence wavelength for a device for modulating the polarization of two-dimensional crystal bandgap fluorescence using an N-type nanograting when θ=30° according to an embodiment of the present invention;

[0061] Figure 11A is a SEM image of an N-type nanograting when θ=45° according to an embodiment of the present invention;

[0062] Figure 11B : is the white light reflection spectrum of the N-type nanograting in the TE direction when θ=45° according to an embodiment of the present invention;

[0063] Figure 11C The fluorescence spectra in the TE and TM directions of the device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using an N-type nanograting when θ=45° according to an embodiment of the present invention are shown;

[0064] Figure 11D This is a graph showing the variation of the fluorescence peak value with the emission angle of the device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal using an N-type nanograting when θ=45° according to an embodiment of the present invention;

[0065] Figure 11E The curve of fluorescence linearity versus fluorescence wavelength for a device that modulates the polarization of the two-dimensional crystal band gap fluorescence using an N-type nanograting when θ=45°;

[0066] Figure 12A SEM image of N-type nanograting when θ=55°;

[0067] Figure 12B White light reflection spectrum of N-type nanograting in TE direction when θ=55°;

[0068] Figure 12C The fluorescence spectra of the device in the TE and TM directions when θ = 55° are obtained by modulating the polarization of the fluorescence band gap of the two-dimensional crystal using an N-type nanograting.

[0069] Figure 12D This is a graph showing the variation of the fluorescence peak value with the emission angle of the device for modulating the polarization of the two-dimensional crystal band gap fluorescence using an N-type nanograting when θ=55° according to an embodiment of the present invention;

[0070] Figure 12E This is a graph showing the variation of fluorescence linearity with fluorescence wavelength for a device for modulating the polarization of two-dimensional crystal bandgap fluorescence using an N-type nanograting when θ=55° according to an embodiment of the present invention.

[0071]

Explanation of symbols

[0072] 1: Substrate

[0073] 2: Insulation layer

[0074] 3: Two-dimensional crystal monolayer

[0075] 4: Transparent medium layer

[0076] 5: Metal nano-metamaterials DETAILED DESCRIPTION

[0077] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0078] The present invention proposes a device for modulating the polarization of the two-dimensional crystal band gap fluorescence. The schematic diagram of the device is shown in FIG. Figure 1 As shown, the device includes: a highly conductive material substrate; an insulating layer formed on the highly conductive material substrate; a two-dimensional crystal monolayer formed on the insulating layer; a light-transmitting medium layer formed on the two-dimensional crystal monolayer; and a metal nano-metamaterial with a periodic unit structure formed on the light-transmitting medium layer.

[0079] In the present invention, the highly conductive material substrate is a highly doped silicon or metal substrate with a thickness of 500-750μm. This flexible and diverse substrate material offers multiple options and is well compatible with silicon-based photonic platforms and micro-nano fabrication technologies. The insulating layer can be made of oxides such as SiO2 and Al2O3, with a thickness of 270-310nm. The two-dimensional crystal monolayer can be made of a transition metal chalcogenide MX2, which is a direct-bandgap semiconductor with strong fluorescence. Where M = Mo, W; X = S, Se, Te; its thickness is less than 1nm. The transparent dielectric layer can be made of Al2O3 or SiO2. This transparent dielectric layer isolates the two-dimensional crystal from the outside world, reducing the effects of factors such as water and oxygen on the crystal, effectively improving the device lifespan. The thickness of the transparent dielectric layer is related to the dielectric constant of the medium. The greater the dielectric constant, the smaller the dielectric layer thickness. Because the dielectric layer thickness affects the resonant transmission and absorption of the excitation field by the metamaterial, the optimal thickness is that which corresponds to the coincidence of the metamaterial's resonant transmission peak with the pump laser wavelength. In the present invention, the thickness of the light-transmitting medium layer is 10-50 nm; the metal nanostructured metamaterial can be made of metal materials such as gold, silver, and aluminum, and its thickness is 30-100 nm.

[0080] Because the metamaterial used in this device is small, unconstrained by the optical diffraction limit, and suitable for on-chip fixed-point integration, the device's size is flexible and adjustable, making it suitable for micro-nano light source modulation. The minimum adjustable area is determined by the metamaterial's structural unit and is on the order of hundreds of nanometers squared, providing a device foundation for the development of chip-scale photonic devices, systems, and functions.

[0081] At the same time, the present invention also provides a method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal. This method is based on the principle of metal surface plasmon resonance, and utilizes the surface plasmon anisotropic resonance mode generated by the metamaterial at the fluorescence wavelength to enhance the resonant electric field in a specific direction, affecting the electric field intensity of the outgoing fluorescence field in this direction, generating polarized fluorescence and achieving the purpose of adjustable polarization. Since the surface plasmon resonance of the metamaterial is the collective resonant behavior of light and electrons on the surface of the metamaterial, it is not affected by temperature. Therefore, the polarization modulation method proposed in the present invention effectively broadens the applicable temperature range; at the same time, the modulation method can broaden the adjustable linearity range. By optimizing the structural design, the degree of coupling between the metamaterial resonance mode and the two-dimensional crystal fluorescence is adjusted to generate fluorescence signals of different linearities. The flow chart of this method is as follows Figure 2 As shown, specifically including:

[0082] Step S201: First, the thickness of the light-transmitting dielectric layer is determined based on the pump light wavelength (i.e., the excitation field wavelength) to achieve strong resonant transmission and absorption of the metamaterial at the excitation field. (Note: Determining the dielectric layer thickness can be performed through numerical simulation).

[0083] Step S202: determining the fluorescence wavelength according to the band gap width of the transition metal chalcogenide as a two-dimensional crystal monolayer.

[0084] Step S203: Determine the period range of the metamaterial nanostructure according to the fluorescence wavelength. The resonant mode of the nanostructure within this period may overlap with the fluorescence wavelength, but not necessarily coincide exactly.

[0085] Step S204: adjusting the air gap inclination angle θ within the metal nano-metamaterial unit structure, fine-tuning the resonant mode position, and obtaining the maximum fluorescence polarization degree. By changing the air gap inclination angle θ, the device can adjust the two-dimensional crystal band gap fluorescence polarization degree from high to low or from low to high.

[0086] Since the surface plasmon resonance characteristics of metamaterials are mainly affected by the shape of the metamaterial, three types of metamaterials are designed in the embodiment of the present invention to modulate the fluorescence linearity, namely nanowire grid, V-shaped nanogrid and N-shaped nanogrid.

[0087] Specifically, WS2 is selected as the two-dimensional crystal monolayer in the device, and N-type silver nanogate is selected as the metal nanostructure metamaterial.

[0088] In step S201, the thickness of the transparent medium layer is determined to be 30 nm according to the pump light wavelength of 532 nm;

[0089] Through step S202, the fluorescence wavelength of WS2 is determined to be ∼630 nm according to the band gap width;

[0090] Through step S203, it is determined based on the fluorescence wavelength of WS2 that the periods of the N-type silver nanostructure in the TE and TM polarization directions are 200 nm and 400 nm respectively;

[0091] In step S204, different air gap inclination angles θ (θ=30°, 45°, 55°) are set, and the corresponding fluorescence linearity is calculated:

[0092] (1) When θ = 30°, the device's linearity near the fluorescence peak at 630 nm is less than 40%. This is because when θ = 30°, the N-type gate surface plasmon resonance position is at 570 nm, which deviates significantly from the fluorescence peak. Therefore, the resonance field has a weak effect on the polarization of the fluorescence field. The high background fluorescence is caused by a weak signal and a low signal-to-noise ratio.

[0093] (2) When θ = 45°, the device achieves a linearity of ~80% near the fluorescence peak of 630nm. This exceptional linearity is due to the fact that when θ = 45°, the surface plasmon resonance of the N-type nanograting in the TE direction is precisely located at the fluorescence wavelength of 630nm, resulting in optimal coupling with the fluorescence field. Driven in this mode, fluorescence in the TE direction smoothly passes through the nanogap, while fluorescence in the TM direction is suppressed, resulting in high fluorescence linearity. This results in a strong fluorescence signal and a high signal-to-noise ratio.

[0094] (3) When θ = 55°, the device exhibits a linearity of ~60% near the fluorescence peak at 630nm, with linearity decreasing rapidly outside the peak. The surface plasmon resonance of this structure is located at ~660nm, and when integrated with WS2, the resulting fluorescence linearity lies between that of the N-type gate at θ = 30° and θ = 45°. The fluorescence signal is strong, and the signal-to-noise ratio is high.

[0095] These results show that changing the angle can shift the surface plasmon resonance position and simultaneously adjust the fluorescence linearity. The highest fluorescence linearity corresponds to the best coupling between the fluorescence wavelength and the metamaterial resonant mode.

[0096] In order to verify the modulation effect of the device for modulating the polarization of the two-dimensional crystal band gap fluorescence proposed in the present invention on the polarization of the two-dimensional crystal band gap fluorescence, the device proposed in the present invention was tested as follows: Figure 3 The test and calculation process shown includes:

[0097] Step S301: A 50X objective lens focuses pump light onto the sample, stimulating the 2D crystal monolayer to emit fluorescence, while simultaneously collecting the fluorescence signal. Fluorescence image acquisition begins with a standard optical microscope equipped with an excitation optical path, sideband filters, and a high-sensitivity CCD imaging system.

[0098] Step S302: Collect the sample's fluorescence spectrum in the TE / TM direction. The TE / TM direction refers to the direction parallel to or perpendicular to the pump laser polarization. In this step, a fluorescence spectrometer (Andor SR-500) is used to collect the fluorescence signal. A polarization analyzer is placed in front of the bandpass filter, and fluorescence signals in different polarization directions are collected by rotating the analyzer.

[0099] Step S303: measuring the spectrum of the sample fluorescence within the range of 0°-360° exit angle, and plotting a graph showing the change of the fluorescence peak value with the exit angle.

[0100] Step S304: By formula L=(I TE -I TM ) / (I TE +I TM )Calculate the fluorescence linearity and draw a curve of the relationship between fluorescence linearity and fluorescence wavelength.

[0101] Example 1: Fluorescence polarization test of WS2 monolayer

[0102] First, a WS2 monolayer is generated on a SiO2 / Si substrate by chemical vapor deposition: sulfur and tungsten powders are heated separately to generate vapor, and argon is used as a carrier gas to carry the vapor to a clean substrate for deposition and growth to obtain a WS2 monolayer.

[0103] Figure 4A is an optical microscopic image of the WS2 monolayer. Figure 4B is the emission fluorescence spectrum in the TE and TM directions obtained by the test in step S302. Figure 4B It can be seen that the fluorescence intensity of the sample is equal in the TE and TM directions, the fluorescence peak of the WS2 monolayer is at ~630nm, the half-maximum width is ~30nm, and the band gap width is 1.9-2.0eV. Figure 4C The graph of the fluorescence spectrum obtained by the test in step S303 as a function of the emission angle is shown. Figure 4C It can be seen that the light intensity of the sample is equal at each output angle. Figure 4D is the curve of fluorescence linearity versus fluorescence wavelength obtained by the test in step S304, Figure 4D It can be seen that the fluorescence linearity of this sample in the forbidden band range is 0.

[0104] Example 2: Device for modulating the polarization of WS2 bandgap fluorescence using Ag nanowire grids

[0105] Since the modulation method proposed in the present invention is based on the surface plasmon resonance principle of metamaterials, which is affected by the shape of the metamaterial, three shapes of metal nano-metamaterials are designed in this example to modulate the fluorescence linearity, namely nanowire grid, V-type nano-grid and N-type nano-grid.

[0106] The period of the unit structure is determined by the fluorescence wavelength of the 2D crystal. For example, the periods of the N-shaped and V-shaped nanostructures in the TE and TM polarization directions can be set to 200nm and 400nm, respectively. This allows the metamaterial's surface plasmon resonance to occur near the fluorescence wavelength of the monolayer WS2, which is approximately 630nm. Further tuning the tilt angle of the air gap within the unit structure can adjust the resonant response to the fluorescence wavelength, thereby achieving a high degree of coupling between the metamaterial and the 2D crystal.

[0107] The three metallic nano-metamaterials have different periods in the TM and TE directions. The wire-grid structure has a TM period of 600-800nm; the N- and V-shaped nano-grids have a TE period of 150-300nm and a TM period of 300-600nm. Compared to the wire-grid structure, the N- and V-shaped nano-structures have more adjustable structural dimensions, particularly the angle θ of the air gap within the structural unit. The present invention precisely adjusts the resonance position by adjusting θ.

[0108] The following describes in detail the process of modulating the polarization of the two-dimensional crystal band gap fluorescence using three structures: nanowire gate, V-type nanogate and N-type nanogate.

[0109] (1) Device for modulating the polarization of WS2 bandgap fluorescence using Ag nanowire grids

[0110] First, a SiO2 insulating layer is obtained on a Si substrate by wet oxidation; then, a WS2 monolayer is grown on the insulating layer by chemical vapor deposition; then, an Al2O3 transparent dielectric layer is evaporated on the monolayer by an electron beam coater; then, an electron beam negative resist MA2403 is spin-coated on the transparent dielectric layer; the negative resist MA2403 is exposed using electron beam direct writing technology, and the structure is written on the negative resist using a focused electron beam; after development, the exposed negative resist MA2403 is retained; finally, after metal evaporation and resist removal processes, an Ag nano-metamaterial is formed to produce a nanowire grid-WS2 monolayer fluorescence polarization modulation device, in which, Figure 5A The SEM image of the Ag nanowire grid in this structure is shown in Figure 2. The period and line width of the silver nanowire grid are b = 600 nm and w = 480 nm.

[0111] Figure 5B The fluorescence spectrum of the nanowire grid-WS2 single layer bandgap fluorescence polarization modulation device in the TE and TM directions obtained by the test in step S302 is: Figure 5B It can be seen that the fluorescence intensity of the nanowire grid-WS2 single-layer bandgap fluorescence polarization modulation device in the TM direction is 40% of that in the TE direction. Figure 5C The variation of the fluorescence peak value with the emission angle obtained by the test in step S303 is Figure 5C It can be seen that the fluorescence shows linear polarization, and the polarization direction is parallel to the nanowire grid. Figure 5DThe curve of fluorescence linearity versus fluorescence wavelength obtained by the test in step S304 is Figure 5D It can be seen that although the fluorescence peak is at 630 nm, the fluorescence linearity is not enhanced at this position, but instead exhibits a broad spectrum response, which is caused by the broad spectrum resonance of the wire grid.

[0112] (2) Device for modulating the polarization of WS2 bandgap fluorescence using V-type Ag nanogratings

[0113] First, a SiO2 insulating layer is formed on a Si substrate by wet oxidation. Then, a WS2 monolayer is grown on the insulating layer by chemical vapor deposition. Then, an Al2O3 transparent dielectric layer is evaporated on the monolayer using an electron beam coating apparatus. Then, an electron beam negative resist MA2403 is spin-coated on the transparent dielectric layer. The negative resist MA2403 is exposed using electron beam direct writing technology, and the structure is written on the negative resist using a focused electron beam. After development, the exposed negative resist MA2403 is retained. Finally, a metal evaporation and resist removal process is performed to form an Ag nanostructure to obtain the device. Figure 6 The V-shaped Ag nanowire grid structure is shown in Figure 3. The period and line width of the nanowire grid are a = 200nm, b = 400nm, s = 50nm, and the air gap tilt angle θ is a variable.

[0114] The fluorescence polarization measurement of the V-type nanograting-WS2 single layer coupling device was carried out below for θ=51° and θ=63°.

[0115] (1)θ=51°

[0116] Figure 7A This is the SEM image of the V-type nanograting when θ=51°. Figure 7B is the white light reflection spectrum of the device in the TE direction, and the reflection valley of 600-650 nm represents the surface plasmon resonance position of the device. Figure 7C is the fluorescence spectrum of the device in the TE and TM directions obtained by the test in step S302. Figure 7C It can be seen that the fluorescence intensity in the TM direction is only 25% of that in the TE direction. Compared with the nanowire grid-WS2 coupling device, the difference between TE and TM intensities becomes larger. Figure 7D The variation of the fluorescence peak value with the emission angle obtained by the test in step S303 is Figure 7D It can be seen that the fluorescence exhibits strong linear polarization, and the polarization direction is parallel to the long axis of the V-shaped grating. Figure 7E This is the curve of fluorescence linearity versus wavelength, obtained through the test in step S304. The peak in the figure is located at ~625nm, coinciding with the surface plasmon resonance, and the linearity is as high as ~60%. Fluorescence linearity remains high beyond 650nm, due to the modulation of the WS2 impurity fluorescence in this range by the metamaterial.

[0117] (2)θ=63°

[0118] Figure 8A This is the SEM image of the V-type nanograting when θ=63°. Figure 8B is the white light reflection spectrum of the device in the TE direction. The reflection valley near 650nm represents the surface plasmon resonance position of the V-type nanograting structure. Figure 8C This is the fluorescence spectrum of the device in the TE and TM directions obtained by the test in step S302. The spectrum results show that there is a large difference in the fluorescence intensity in the two perpendicular directions. Figure 8D The variation law of the fluorescence peak value with the emission angle obtained by the test in step S303 is: Figure 8D It can be seen that the fluorescence shows strong linear polarization, and the polarization direction is parallel to the long axis of the V-shaped grating. Figure 8E is the curve of fluorescence linearity versus fluorescence wavelength obtained by the test in step S304, Figure 8E As can be seen, the linearity exhibits a distinct peak near 640nm, reaching approximately 60%. The linearity outside this peak decreases rapidly. This is because when θ = 63°, the surface plasmon resonance of the V-shaped nanograting in the TE direction occurs near 650nm, strongly modulating the fluorescence signal only at this location. The high background fluorescence may be due to a poor debonding process, leaving residual adhesive luminescent.

[0119] (III) Device for modulating the polarization of WS2 bandgap fluorescence using N-type Ag nanogates

[0120] First, a SiO2 insulating layer is formed on a Si substrate by wet oxidation; then, a WS2 monolayer is grown on the insulating layer by chemical vapor deposition; then, an Al2O3 transparent dielectric layer is evaporated on the monolayer using an electron beam coater; then, an electron beam negative resist MA2403 is spin-coated on the transparent dielectric layer, and the structure is written on the negative resist using a focused electron beam; the negative resist MA2403 is exposed using electron beam direct writing technology; the exposed negative resist MA2403 is retained after development; finally, a metal evaporation and resist removal process is performed to form an Ag nanostructure to obtain the device, wherein, Figure 9 The structure of the N-type Ag nanowire grid in this structure is shown in Figure 2. The period and line width of the nanowire grid in this structure are a = 200nm, b = 400nm, s = 50nm, and the air gap tilt angle θ is a variable.

[0121] The fluorescence polarization test of the N-type nanograting-WS2 single-layer coupling device is performed below when θ=30°, θ=45°, and θ=55°.

[0122] (1)θ=30°

[0123] Figure 10A This is the SEM image of the N-type nanograting when θ = 30°. Figure 11Bis the white light reflection spectrum of the device in the TE direction, from which we can know that the surface plasmon resonance position is at 570nm. Figure 10C is the fluorescence spectrum of the device in the TE and TM directions obtained by the test in step S302. Figure 10C It can be seen that there is a large difference in the fluorescence intensity in the two perpendicular directions, and the background fluorescence is very high. Figure 10D This is a graph showing the variation of the fluorescence peak value with the emission angle obtained by the test in step S303. It can be seen that the fluorescence has linear polarization, but it is not strong, and the polarization direction is parallel to the long axis of the N-type gate. Figure 10E This is the curve of fluorescence linearity versus fluorescence wavelength, obtained in step S304. The linearity near the fluorescence peak at 630nm is less than 40%. This is because when θ = 30°, the surface plasmon resonance position of the N-type gate is at 570nm, significantly deviating from the fluorescence peak. Therefore, the resonance field has a weak effect on the polarization of the fluorescence field. High background fluorescence occurs because the small θ value results in weak emitted fluorescence and a low signal-to-noise ratio.

[0124] (2)θ=45°

[0125] Figure 11A This is the SEM image of the N-type nanograting when θ = 45°. Figure 11B is the white light reflection spectrum of the device in the TE direction, from which we can know that the surface plasmon resonance position is at 630nm. Figure 11C The fluorescence spectrum of the device in the TE and TM directions is obtained by the test in step S302. Figure 11C It can be seen that the fluorescence intensity in the two perpendicular directions has the greatest difference. At the same time, the emitted fluorescence signal is strong, the background is weak, and the signal-to-noise ratio is high. Figure 11D This is a graph showing how the fluorescence peak value changes with the emission angle, as measured in step S303. It can be seen from the graph that the fluorescence exhibits strong linear polarization, with the polarization direction being parallel to the long axis of the N-type gate. Figure 11E This is the curve of fluorescence linearity versus fluorescence wavelength, obtained through the test in step S304. This curve shows that the linearity is ~80% near the fluorescence peak at 630nm. This structure exhibits exceptional linearity because when θ = 45°, the surface plasmon resonance of the N-type nanograting in the TE direction is precisely at the fluorescence wavelength, resulting in the strongest modulation of the fluorescence field. Driven in this mode, fluorescence in the TE direction smoothly passes through the nanogap, while fluorescence in the TM direction is suppressed, resulting in high fluorescence linearity.

[0126] (3)θ=55°

[0127] Figure 12A This is the SEM image of the θ=55° N-type nanograting. Figure 12B is the white light reflection spectrum of the device in the TE direction, from which we can know that the surface plasmon resonance position is at 660nm. Figure 12Cis the fluorescence spectrum of the device in the TE and TM directions obtained by the test in step S302. Figure 12C As can be seen, there is a significant difference in fluorescence intensity between the two perpendicular directions, while the outgoing fluorescence signal is strong, the background is weak, and the signal-to-noise ratio is high. Due to the weakened fluorescence suppression ability in the TM direction, the difference in fluorescence intensity in the TE / TM direction is reduced compared to the N-type grating with θ = 45°. Figure 12D This is a graph showing how the fluorescence peak value changes with the emission angle obtained by the test in step S303. As can be seen from the graph, the fluorescence exhibits strong linear polarization, and the polarization direction is parallel to the long axis of the N-type gate. Figure 12E This is a curve showing the variation of fluorescence linearity with fluorescence wavelength, obtained through the test in step S304. As can be seen, the linearity is ~60% near the fluorescence peak at 630nm, while the linearity decreases rapidly outside the peak. The surface plasmon resonance of this structure is located at ~660nm. After integration with WS2, the fluorescence linearity achieved lies between that achieved with the N-type gate at θ = 30° and θ = 45°, demonstrating that varying the angle can alter the surface plasmon resonance position and simultaneously adjust the fluorescence linearity.

[0128] Example 3:

[0129] In addition to the above systems, a preferred two-dimensional crystal is a single layer of WSe2. A WSe2 single layer has higher quantum efficiency and a longer fluorescence wavelength of 750nm. The structure and process for preparing a metamaterial-two-dimensional crystal bandgap fluorescence polarization modulation device from this WSe2 single layer are the same as those in Example 2. The selected nanostructure period is determined by the fluorescence wavelength, and the selected dielectric layer thickness is determined by the excitation light wavelength. The principles for this development are explained in the technical solution introduction. Generally, as the wavelength increases, the metal dissipation decreases, the surface plasmon resonance response increases, and the fluorescence linearity modulation effect improves.

[0130] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A device for modulating the polarization of two-dimensional crystal bandgap fluorescence, comprising: a highly conductive material substrate; An insulating layer formed on the highly conductive material substrate, wherein the insulating layer is SiO2 or Al2O3; A two-dimensional crystal monolayer formed on the insulating layer, wherein the two-dimensional crystal monolayer is a transition metal chalcogenide compound MX2, where M=Mo, W; X=S, Se, Te; a light-transmitting medium layer formed on the two-dimensional crystal monolayer; and A metal nano-metamaterial with a periodic unit structure is formed on the light-transmitting medium layer.

2. The device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal according to claim 1, wherein the highly conductive material substrate is a highly doped silicon or metal substrate with a thickness of 500-750 μm; the highly conductive material plays a structural support role and reflects the fluorescence emitted by the two-dimensional crystal monolayer.

3. The device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal according to claim 1, wherein the thickness of the insulating layer is 270-310 nm; and the insulating layer serves as a growth substrate for the two-dimensional crystal monolayer.

4. The device for modulating the polarization of two-dimensional crystal bandgap fluorescence according to claim 1, wherein the thickness of the two-dimensional crystal monolayer is less than 1 nm; and the two-dimensional crystal monolayer emits fluorescence under the excitation of pump light.

5. The device for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal according to claim 1, wherein the transparent dielectric layer is Al2O3 or SiO2 and has a thickness of 10-50 nm; the thickness of the transparent dielectric layer affects the resonant transmission and absorption of the metal nano-metamaterial in the excitation field, further affecting the fluorescence intensity; and the transparent dielectric layer protects the two-dimensional crystal material from the influence of water, oxygen or impurity ions. 6 . The device for modulating the polarization of two-dimensional crystal bandgap fluorescence according to claim 1 , wherein the metal nano-metamaterial is a nanostructure of gold, silver or aluminum with a thickness of 30-100 nm.

7. The device for modulating the polarization of two-dimensional crystal bandgap fluorescence according to claim 1, wherein: The metal nano-metamaterial with a periodic unit structure has a linear, V-shaped or N-shaped air gap structure; The angle between the V-shaped or N-shaped air gap structure and the horizontal direction is the air gap inclination angle θ.

8. A method for modulating the polarization of two-dimensional crystal bandgap fluorescence, based on the device for modulating the polarization of two-dimensional crystal bandgap fluorescence according to any one of claims 1 to 7, the method comprising: The thickness of the light-transmitting medium layer is determined according to the wavelength of the pump light, i.e., the wavelength of the excitation field, to achieve strong resonant transmission and absorption of the metamaterial at the excitation field. determining a fluorescence wavelength according to the band gap width of the two-dimensional crystal monolayer, i.e., a monolayer transition metal chalcogenide; Determine the period range of the metal nano-metamaterial unit structure based on the fluorescence wavelength; By adjusting the air gap inclination angle θ within the metal nano-metamaterial unit structure, the resonant mode position is fine-tuned to obtain the maximum fluorescence polarization degree.

9. The method for modulating the polarization of the two-dimensional crystal band gap fluorescence according to claim 8, wherein: In the step of determining the period range of the metal nano-metamaterial according to the fluorescence wavelength, after the period is determined, the surface plasmon resonance mode of the metamaterial is ensured to be located near the fluorescence wavelength, but not necessarily exactly at the fluorescence wavelength.

10. The method for modulating the polarization of the bandgap fluorescence of a two-dimensional crystal according to claim 8, wherein in the step of adjusting the air gap inclination angle θ within the metal nano-metamaterial unit structure, the device adjusts the polarization of the bandgap fluorescence of the two-dimensional crystal from high to low or from low to high by adjusting the air gap inclination angle θ.

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