An efficient SPP coupler and its manufacturing method

Abstract

The present invention relates to a high-efficiency SPP coupler and a preparation method thereof. The coupler includes a substrate, a metal thin film layer, a dielectric thin film layer, a dielectric grating layer, and an asymmetric metal grating structure; the metal thin film layer is connected to the substrate, and the dielectric thin film layer is connected to the metal thin film layer, the dielectric grating layer, and the asymmetric metal grating structure respectively. The present invention can realize that the dielectric thin film layer couples the unidirectional transmission SPP generated by the asymmetric metal grating structure to the metal thin film layer, playing a role in preventing SPP quenching and improving the SPP coupling efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of surface plasmon components, and in particular to a high-efficiency SPP coupler and a manufacturing method thereof. Background Art

[0002] Surface Plasmon Polariton (SPP) is a collective oscillation phenomenon of free electrons or bound electrons on the surface of a metal structure induced by an external electromagnetic field. It can localize the incident light in a sub-wavelength region on the metal surface, break through the diffraction limit constraint, and realize the modulation of light and enhance the interaction between light and matter at the nanoscale, which is of crucial significance for realizing an integrated optical circuit with both extremely small feature sizes and ultra-high transmission speeds.

[0003] The SPP unidirectional coupler is one of the important components of the integrated optical circuit. Through a specially designed coupling interface, the light wave propagating in free space can be coupled into the plasmon system and converted into a surface plasmon with controllable direction. However, how to design a metal micro-nano structure so that light can be efficiently coupled to the metal micro-nano structure to form a unidirectionally transmitted SPP is still one of the important problems at present. In addition, the existing SPP coupler structures usually have complex preparation processes and high requirements for equipment conditions, which become a major factor restricting their large-scale application. Therefore, reducing the manufacturing difficulty is another important issue that needs to be considered. Summary of the Invention

[0004] To solve the technical problems existing in the prior art, the present invention provides a high-efficiency SPP coupler and a manufacturing method thereof. The unidirectionally transmitted SPP generated by the asymmetric metal grating structure is coupled to the metal thin film layer through a dielectric thin film layer, which plays a role in preventing SPP quenching and improving the SPP coupling efficiency.

[0005] The present invention is implemented by the following technical solutions: A high-efficiency SPP coupler includes a metal thin film layer, a dielectric thin film layer, a dielectric grating layer, and an asymmetric metal grating structure; the metal thin film layer is connected to a substrate, and the dielectric thin film layer is respectively connected to the metal thin film layer, the dielectric grating layer, and the asymmetric metal grating structure.

[0006] The manufacturing method of the high-efficiency SPP coupler of the present invention is based on the above high-efficiency SPP coupler. A metal thin film layer is formed on the substrate by magnetron sputtering; a dielectric thin film layer is formed on the metal thin film layer by magnetron sputtering; a photoresist is formed on the dielectric thin film layer by spin coating and dried; a grating layer of the photoresist is formed by double-beam interference exposure and development or by nanoimprinting, and then a dielectric grating layer of the photoresist is formed by dry etching; an "inverted L" shape or a "Z" - shaped asymmetric metal grating structure is formed on the photoresist by evaporation coating.

[0007] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0008] 1. The present invention can realize that the dielectric thin film layer couples the unidirectional transmission SPP generated by the asymmetric metal grating structure to the metal thin film layer, which plays a role in preventing SPP quenching and improving the SPP coupling efficiency.

[0009] 2. By setting the thickness of the dielectric thin film layer, the present invention enables the dielectric thin film layer to act as a waveguide, realizing the direct transmission of SPP in the dielectric layer.

[0010] 3. The manufacturing method of the present invention is simple and easy to implement, with a simple process and high process compatibility, and is suitable for large-scale processing and preparation. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is the structural diagram of the high-efficiency SPP coupler in Embodiment 1 of the present invention;

[0012] Figure 2 is the schematic diagram of the metal thin film layer of the present invention separating the substrate and the dielectric thin film layer;

[0013] Figure 3 is the schematic diagram of the dielectric thin film layer of the present invention separating the metal thin film layer and the dielectric grating layer;

[0014] Figure 4 is the structural diagram of the high-efficiency SPP coupler in Embodiment 2 of the present invention;

[0015] Figure 5 is the schematic diagram of the sample evaporation of the present invention;

[0016] Figure 6 is the energy flow distribution diagram of the single inverted "L" - shaped asymmetric metal grating structure of the present invention perpendicular to the grating bar direction;

[0017] In the figure, 11 is the substrate, 12 is the metal thin film layer, 13 is the dielectric thin film layer, 21 is the dielectric grating layer, 41 is the asymmetric metal grating structure; 31 is the inclined fixing device; 51 is the crucible. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] The present invention will be further described in detail below with reference to the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0019] Embodiment 1

[0020] As Figure 1As shown in the figure, the high-efficiency SPP coupler in this embodiment mainly includes: a substrate 11, a metal thin film layer 12, a dielectric thin film layer 13, a dielectric grating layer 21, and an asymmetric metal grating structure 41; the metal thin film layer 12 is connected to the substrate 11, and the dielectric thin film layer 13 is respectively connected to the metal thin film layer 12, the dielectric grating layer 21, and the asymmetric metal grating structure 41.

[0021] Specifically, the substrate is quartz, mica, PDMS, sapphire, or other materials with high transmittance in the range of 300 - 1600 nm; the metal thin film layer separates the substrate and the dielectric thin film layer, as Figure 2 shown; the dielectric thin film layer separates the metal thin film layer and the dielectric grating layer, as Figure 3 shown; the dielectric thin film layer separates the metal thin film layer and the asymmetric metal grating structure, and the refractive index of the dielectric thin film layer is between 1.4 and 2.5.

[0022] Specifically, the thickness of the dielectric thin film layer is 5 - 50 nm. The dielectric thin film layer couples the unidirectional transmission SPP generated by the asymmetric metal grating structure to the metal thin film layer, playing a role in preventing SPP quenching and improving the SPP coupling efficiency; the thickness of the metal thin film layer is 10 - 100 nm, and the role of the metal thin film layer is to serve as a medium for SPP propagation.

[0023] The refractive index of the dielectric in the dielectric grating layer is between 1.4 and 1.7; the grating period is 300 - 800 nm; preferably, the grating period is 400 - 600 nm.

[0024] The asymmetric metal grating structure is in an "inverted L" shape or a "Z" shape, and the asymmetric metal grating structure covers a part of the dielectric grating layer; preferably, the metal thickness of the asymmetric metal grating structure is greater than 50 nm; preferably, the metal thickness of the asymmetric metal grating structure is between 70 - 150 nm.

[0025] Embodiment 2

[0026] As shown in Figure 4, the high-efficiency SPP coupler in this embodiment mainly includes: a substrate 11, a metal thin film layer 12, a dielectric thin film layer 13, a dielectric grating layer 21, and an asymmetric metal grating structure 41; the metal thin film layer 12 is connected to the substrate 11, and the dielectric thin film layer 13 is respectively connected to the metal thin film layer 12, the dielectric grating layer 21, and the asymmetric metal grating structure 41.

[0027] Specifically, the substrate is quartz, mica, PDMS, sapphire, or other materials with high transmittance in the range of 300 - 1600 nm; the metal thin film layer separates the substrate and the dielectric thin film layer; the dielectric thin film layer separates the metal thin film layer and the dielectric grating layer; the dielectric thin film layer separates the metal thin film layer and the asymmetric metal grating structure, and the refractive index of the dielectric thin film layer is between 1.4 and 2.5.

[0028] Specifically, the thickness of the dielectric thin film layer is 300 - 800 nm. If the dielectric thin film layer is within this range, the dielectric thin film layer functions as a waveguide, and the SPP directly propagates in the dielectric layer; the thickness of the metal thin film layer is 100 - 200 nm, which serves to confine the SPP.

[0029] The refractive index of the dielectric in the dielectric grating layer is between 1.4 and 1.7; the grating period is 300 - 800 nm; preferably, the grating period is 400 - 600 nm.

[0030] The asymmetric metal grating structure is in the shape of an "inverted L" or a "Z" - shape, and the asymmetric metal grating structure covers a part of the dielectric grating layer; preferably, the metal thickness of the asymmetric metal grating structure is greater than 50 nm; preferably, the metal thickness of the asymmetric metal grating structure is between 70 - 150 nm.

[0031] Based on the high - efficiency SPP coupler disclosed in the above - mentioned embodiments, this embodiment further discloses a preparation method of a high - efficiency SPP coupler. A metal thin film layer is formed on a substrate by magnetron sputtering; a dielectric thin film layer is formed on the metal thin film layer by magnetron sputtering; a photoresist is formed on the dielectric thin film layer by spin - coating and dried; a grating layer of the photoresist is formed by double - beam interference exposure and development or by nano - imprinting method, and then a dielectric grating layer of the photoresist is formed by dry etching; an asymmetric metal grating structure in the shape of an "inverted L" or a "Z" - shape is formed on the photoresist by evaporation coating.

[0032] The preparation method of the high - efficiency SPP coupler of the present invention can be carried out in two ways according to the thickness of the dielectric thin film layer being 5 - 50 nm and the thickness of the dielectric thin film layer being 300 - 800 nm. The following are detailed descriptions through two embodiments respectively.

[0033] Embodiment 3

[0034] In this embodiment, by forming a dielectric thin film layer with a thickness of 5 - 50 nm, the specific steps of the preparation method of the high - efficiency SPP coupler of the present invention are as follows:

[0035] S11. A nickel - gold (Ni / Au) thin film layer with a thickness of 5 nm or 50 nm is successively formed on a quartz substrate by magnetron sputtering.

[0036] S12. A SiO2 dielectric thin film layer with a thickness of 50 nm is formed on the nickel - gold (Ni / Au) thin film layer by magnetron sputtering.

[0037] S13. A photoresist with a thickness of 200 nm is formed on the surface of the SiO2 dielectric thin film layer by spin - coating and dried.

[0038] S14. Form a grating layer of photoresist by double-beam interference exposure and development or by nanoimprinting, and then form a dielectric grating layer of photoresist by dry etching. Among them, the grating period is 550 nm and the grating bar width is 200 nm.

[0039] S15. Place the sample formed by the quartz substrate, nickel-gold (Ni / Au) thin film layer, SiO2 dielectric thin film layer and dielectric grating layer on the tilting fixing device 31 fixed in the cavity at a certain tilting angle, and use the crucible 51 for evaporation, as Figure 5 shown. The arrow direction is the electron beam direction. Optionally, the angle of the tilting fixing device is continuously adjustable. During evaporation, the angle of the device can be adjusted during the evaporation process according to the change of the metal thickness. According to the period and duty cycle of the grating, the tilting angle is between 30° and 60°, as Figure 5 shown.

[0040] S16. Perform inclined evaporation using the evaporation method in step S15 to form an inverted "L"-shaped asymmetric metal grating structure on the photoresist. Among them, the thickness h of the metal thin film layer is 200 nm.

[0041] By simulating the unidirectional transmission effect of the device formed by the above preparation method steps, as Figure 6 shown, when the wavelength is 840 nm, the energy flow distribution diagram of a single inverted "L"-shaped asymmetric metal grating structure perpendicular to the grating bar direction (i.e., the x direction). The energy flow of the SPP coupler is mainly distributed within about 200 nm of the lower surface of the nickel-gold thin film layer and propagates along the negative x direction. This is different from the energy flow of a common symmetric grating that propagates in two directions. That is, this structure achieves the unidirectional transmission effect of the SPP coupler and can be well restricted to propagate within the substrate. When extracting the SPP coupler signal subsequently, only the transmission condition needs to be broken at a specific position. For example, by etching a groove structure on the substrate surface, the SPP coupler emits light through scattered light.

[0042] Example 4

[0043] In this example, by forming a dielectric thin film layer with a thickness of 300 - 800 nm, the specific steps of the preparation method of the high-efficiency SPP coupler of the present invention are as follows:

[0044] S21. Sequentially form a nickel-silver (Ni / Ag) thin film layer with a thickness of 3 nm or 100 nm on the quartz substrate by magnetron sputtering.

[0045] S22. Form a SiNx dielectric thin film layer with a thickness of 500 nm on the nickel-silver (Ni / Ag) thin film layer by magnetron sputtering.

[0046] S23. Spin-coat a photoresist with a thickness of 200 nm on the surface of the SiNx dielectric thin film layer and dry it.

[0047] S24. Form a grating layer of photoresist by double-beam interference exposure and development or by nanoimprinting, and then form a dielectric grating layer of photoresist by dry etching. Among them, the grating period is 800 nm and the grating bar width is 200 nm.

[0048] S25. Place the sample formed by the quartz substrate, nickel-silver (Ni / Ag) thin film layer, SiNx dielectric thin film layer, and dielectric grating layer on the tilt fixing device fixed in the cavity at a certain tilt angle, and use a crucible for evaporation coating. Optionally, the angle of the tilt fixing device is continuously adjustable. During evaporation coating, the angle of the device can be adjusted during the evaporation coating process according to the thickness change. According to the period and duty cycle of the grating, the tilt angle is between 30° and 60°.

[0049] S26. Perform tilt evaporation coating using the evaporation coating method in step S25 to form an inverted "Z"-shaped asymmetric metal grating structure on the photoresist. Among them, the thickness h of the metal thin film layer is 200 nm.

[0050] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An efficient SPP coupler, characterized in that, It includes a substrate, a metal thin film layer, a dielectric thin film layer, a dielectric grating layer, and an asymmetric metal grating structure; the metal thin film layer is connected to the substrate, and the dielectric thin film layer is respectively connected to the metal thin film layer, the dielectric grating layer, and the asymmetric metal grating structure; The metal thin film layer separates the substrate and the dielectric thin film layer, the dielectric thin film layer separates the metal thin film layer and the dielectric grating layer, and the dielectric thin film layer separates the metal thin film layer and the asymmetric metal grating structure; The refractive index of the dielectric thin film layer is between 1.4 and 2.5, the refractive index of the dielectric in the dielectric grating layer is between 1.4 and 1.7, and the grating period is 300 - 800 nm; When the thickness of the dielectric thin film layer is 5 - 50 nm, the thickness of the metal thin film layer is 10 - 100 nm; or when the thickness of the dielectric thin film layer is 300 - 800 nm, the thickness of the metal thin film layer is 100 - 200 nm; The dielectric thin film layer is a SiO2 dielectric thin film layer or a SiNx dielectric thin film layer; The asymmetric metal grating structure is in an "inverted L" shape or a "Z" shape, and the asymmetric metal grating structure covers the dielectric grating layer.

2. The high-efficiency SPP coupler according to claim 1, characterized in that, The substrate is quartz, mica, PDMS, or sapphire.

3. The preparation method of the high-efficiency SPP coupler according to claim 1, characterized in that, The metal thin film layer is formed on the substrate by magnetron sputtering; the dielectric thin film layer is formed on the metal thin film layer by magnetron sputtering; a photoresist is formed on the dielectric thin film layer by spin coating and dried; a grating layer of the photoresist is formed by double-beam interference exposure and development or by nanoimprinting, and then a dielectric grating layer of the photoresist is formed by dry etching; An "inverted L" shape or a "Z" shape asymmetric metal grating structure is formed on the photoresist by evaporation coating.

4. The preparation method of the high-efficiency SPP coupler according to claim 3, wherein, The specific preparation steps for the dielectric thin film layer with a thickness of 5 - 50 nm are as follows: S11. A nickel-gold thin film layer with a thickness of 5 nm or 50 nm is formed on a quartz substrate by magnetron sputtering; S12. A SiO2 dielectric thin film layer with a thickness of 50 nm is formed on the nickel-gold thin film layer by magnetron sputtering; S13. A photoresist with a thickness of 200 nm is formed on the surface of the SiO2 dielectric thin film layer by spin coating and dried; S14. A grating layer of the photoresist is formed by double-beam interference exposure and development or by nanoimprinting, and then a dielectric grating layer of the photoresist is formed by dry etching; wherein, the grating period is 550 nm and the grating bar width is 200 nm; S15. The sample formed by the quartz substrate, the nickel-gold thin film layer, the SiO2 dielectric thin film layer, and the dielectric grating layer is placed obliquely on an inclined fixing device fixed in the cavity for evaporation coating; S16. The inclined evaporation coating is carried out by the evaporation coating method in step S15 to form an inverted "L" type asymmetric metal grating structure on the photoresist.

5. The preparation method of the high-efficiency SPP coupler according to claim 3, wherein, The specific preparation steps for the dielectric thin film layer with a thickness of 300 - 800 nm are as follows: S21. A nickel-silver thin film layer with a thickness of 3 nm or 100 nm is formed on a quartz substrate by magnetron sputtering; S22. A SiNx dielectric thin film layer with a thickness of 500 nm is formed on the nickel-silver thin film layer by magnetron sputtering; S23. A photoresist with a thickness of 200 nm is formed on the surface of the SiNx dielectric thin film layer by spin coating and dried; S24. A grating layer of photoresist is formed by double-beam interference exposure and development or by nanoimprinting, and then a dielectric grating layer of photoresist is formed by dry etching; wherein, the grating period is 800 nm and the grating bar width is 200 nm; S25. The sample formed by the quartz substrate, the nickel-silver thin film layer, the SiNx dielectric thin film layer and the dielectric grating layer is placed obliquely on the inclined fixing device fixed in the cavity for evaporation coating; S26. The inclined evaporation coating is carried out by the evaporation coating method in step S25 to form an inverted "Z"-shaped asymmetric metal grating structure on the photoresist.

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