A tunable surface plasmon excitation structure

Abstract

The application discloses a tunable surface plasmon excitation structure and belongs to the technical field of micro-nano photoelectronic technology, which comprises a substrate, a metal film is arranged on the substrate, an asymmetric slot is arranged on the metal film, the slot comprises a small groove and a large groove, PMMA polymer is arranged in the small groove, polyimide orientation layers are arranged on both sides of the inside of the large groove, a liquid crystal layer is arranged in the middle of the large groove, a layer of PMMA polymer is arranged on the top surface of the metal film, the metal films on both sides of the slot are isolated and disconnected, an external voltage is arranged on the metal films on both sides of the slot, the liquid crystal layer is in an electric field formed by the external voltage, the refractive index of the liquid crystal layer is changed by adjusting the external voltage, and thus the size of the surface plasmon electric field amplitude is realized. The tunable surface plasmon excitation structure has the characteristics of simple structure, convenient implementation, rapid response, small integration and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of micro-nano optoelectronics, and particularly relates to a tunable surface plasmon excitation structure. BACKGROUND

[0002] Surface plasmon is a surface electromagnetic wave existing at the interface of metal and dielectric, the propagation direction of which is parallel to the interface of metal and dielectric, and the wavelength of which is shorter than that of the free space electromagnetic wave of the same frequency. In the vertical direction of the interface of metal and dielectric, the amplitude thereof is exponentially attenuated, the electromagnetic field is tightly limited at the interface of metal and dielectric, and the subwavelength constraint characteristic of breaking the diffraction limit is presented. The above excellent characteristics make surface plasmon have rich application prospects in the fields of optical manipulation and optoelectronic integrated devices.

[0003] In order to explore the dynamic tunability of the intensity of surface plasmon, the application provides a surface plasmon excitation structure, which provides a new technical path for optoelectronic integration and particle manipulation in nanoscale, and promotes the application development in the technical field of surface plasmon optical tweezers. SUMMARY

[0004] In order to achieve the above purpose, the application provides a tunable surface plasmon excitation structure. By adjusting the applied voltage to change the refractive index of the liquid crystal layer, the electric field amplitude of the surface plasmon is controlled, and the tunable surface plasmon excitation structure provided by the application has the characteristics of simple structure, convenient implementation, rapid response, and being conducive to small integration.

[0005] A tunable surface plasmon excitation structure, comprising a substrate, a metal film is arranged on the substrate, the metal film is provided with an asymmetric slot, the slot comprises a small slot and a large slot, the side edge of one side of the small slot and the side edge of the same side of the large slot are aligned, the small slot and the large slot are rectangular slots, an optical medium 1 is arranged in the small slot, an electrically controlled birefringent material is arranged in the large slot, an optical medium 2 is arranged on the top surface of the metal film, the optical medium 2 covers the top surface of the metal film, the electrically controlled birefringent material is applied with an applied voltage, the excitation incident light is perpendicularly incident into the tunable surface plasmon excitation structure in the direction from the small slot to the large slot, and the transmittance of the excitation incident light relative to the substrate is not 0.

[0006] Further, the substrate is a glass substrate.

[0007] Further, the metal film is one of a gold film or a silver film.

[0008] Further, the optical medium 1 and the optical medium 2 are both PMMA polymers.

[0009] Further, the electrically controlled birefringent material is composed of orientation layers on both sides and a liquid crystal layer in the middle, the liquid crystal layer is in the electric field formed by the applied voltage, the refractive index of the liquid crystal layer is changed by adjusting the applied voltage, so as to control the amplitude of the surface plasmon electric field.

[0010] Further, the metal film on both sides of the slit is isolated and insulated from being disconnected, and the applied voltage is arranged on the metal film on both sides of the slit.

[0011] Further, the orientation layer is a polyimide orientation layer.

[0012] Further, the excitation incident light is linearly polarized light with a wavelength of 700nm, and the polarization direction is perpendicular to the slit direction.

[0013] The present application has the following beneficial effects:

[0014] The tunable surface plasmon excitation structure provided by the present application can flexibly control the amplitude of the surface plasmon electric field by adjusting the applied voltage to change the refractive index of the liquid crystal layer, and has the characteristics of simple structure, convenient implementation, rapid response, and being conducive to small integration. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The schematic diagram of the tunable surface plasmon excitation structure of the present application

[0016] Figure 2 The schematic diagram of the side cross-sectional structure of the tunable surface plasmon excitation structure of the present application

[0017] Figure 3 The surface plasmon electric field amplitude distribution diagram of the tunable surface plasmon excitation structure of the present application when the refractive index of the liquid crystal layer is 1.5

[0018] Figure 4 The surface plasmon electric field amplitude distribution diagram of the tunable surface plasmon excitation structure of the present application when the refractive index of the liquid crystal layer is 1.58

[0019] Figure 5 The surface plasmon electric field amplitude distribution diagram of the tunable surface plasmon excitation structure of the present application when the refractive index of the liquid crystal layer is 1.64

[0020] Figure 6 The surface plasmon electric field amplitude distribution diagram of the tunable surface plasmon excitation structure of the present application when the refractive index of the liquid crystal layer is 1.7

[0021] Figure 7 The relationship diagram between the surface plasmon electric field amplitude and the refractive index of the liquid crystal layer of the tunable surface plasmon excitation structure of the present application.

[0022] Figure: 1, substrate; 2, metal film; 3, liquid crystal layer; 4, polyimide orientation layer; 5, PMMA polymer; 6, small slot; 7, large slot; 8, excitation incident light. DETAILED DESCRIPTION

[0023] To make the purpose, technical solutions and advantages of the present application more clear and obvious, the following will combine specific embodiments and refer to the attached drawings. Figures 1-7 The present application is further described in detail. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present application.

[0024] A tunable surface plasmon excitation structure, the structural schematic diagram is as shown in Figure 1 and Figure 2 , Figure 1 is a schematic diagram of the tunable surface plasmon excitation structure of the present application, Figure 2 is a schematic diagram of the side profile structure of the tunable surface plasmon excitation structure of the present application along the AA' plane in Figure 1 , including a substrate 1, the substrate 1 is provided with a metal film 2, the metal film 2 is provided with an asymmetric slit, the slit includes a small slot 6 and a large slot 7, the side edge of one side of the small slot 6 and the side edge of the same side of the large slot 7 are aligned, the small slot 6 and the large slot 7 are both rectangular slots, the slot width of the small slot 6 is w 1=0.15um, the slot height h 1=0.12um, the slot width of the large slot 7 is w 2=0.543um, the slot height h 2=0.13um, the small slot 6 is provided with a PMMA polymer 5, the two sides inside the large slot 7 are provided with a polyimide orientation layer 4 with a thickness of w 3=0.06um, the rest of the space inside the large slot 7 is provided with a liquid crystal layer 3, the metal film 2 on both sides of the slit is isolated and disconnected, an external voltage is provided on the metal film 2 on both sides of the slit, so that the liquid crystal layer 3 is in the electric field formed by the external voltage, and the top surface of the metal film 2 is provided with a layer of PMMA polymer 5.

[0025] Among them, the substrate 1 adopts BK7 glass substrate, the liquid crystal layer 3 is nematic liquid crystal material E7, the excitation incident light 8 is normally incident in the direction from the small slot 6 to the large slot 7, that is, the excitation incident light 8 is normally incident from the side of the glass substrate, the excitation incident light 8 is linearly polarized light with a wavelength of 700nm, the polarization direction is perpendicular to the direction of the slit, and the amplitude of the excitation incident light 8 is 1. For the excitation incident light 8, the refractive index of the BK7 glass substrate is 1.52, the refractive index of the PMMA polymer 5 is 1.49, and the refractive index of the polyimide orientation layer 4 is 1.68. The metal film 2 is a gold film with a thickness of 250nm.

[0026] The surface plasmon field amplitude distribution diagram of the tunable surface plasmon excitation structure is as shown in Figures 3-6 As shown in the figure, Figure 3 is the surface plasmon field amplitude distribution diagram when the refractive index of the liquid crystal layer 3 is 1.5 under the applied voltage, at this time, the field amplitude of the surface plasmon excited on the right side of the upper surface of the gold film at a distance of 2um from the center of the small groove 6 is 0.45, Figure 4 、 Figure 5 and Figure 6 is the surface plasmon field amplitude distribution diagram under the condition of continuously changing the voltage value of the applied voltage, Figure 4 、 Figure 5 and Figure 6 The refractive index corresponding to the liquid crystal layer 3 is 1.58, 1.64, and 1.7, respectively, Figure 4 、 Figure 5 and Figure 6 The field amplitude of the corresponding position is 0.414, 0.358, and 0.243, respectively. Therefore, the field amplitude changes significantly after changing the applied voltage, and the tunable surface plasmon excitation structure provided by the present application has a significant effect.

[0027] Further as shown in Figure 7 , Figure 7 is a relationship diagram of the surface plasmon field amplitude and the refractive index of the liquid crystal layer on the right side of the upper surface of the gold film at a distance of 2um from the center of the small groove 6, the refractive index of the liquid crystal layer 3 is changed by adjusting the applied voltage to change the field amplitude of the surface plasmon, when the refractive index of the liquid crystal layer 3 is 1.5 under the applied voltage, at this time, the field amplitude of the surface plasmon on the right side of the upper surface of the gold film at a distance of 2um from the center of the small groove 6 is 0.45, in the process of continuously changing the applied voltage, the refractive index of the liquid crystal layer 3 increases from 1.5 to 1.7, in this process, the field amplitude of the surface plasmon at the corresponding position decreases from 0.45 to 0.243, by adjusting the applied voltage, the size of the surface plasmon field amplitude is flexibly controlled, and the operation is convenient.

Claims

1. A tunable surface plasmon excitation structure, characterized by: The application relates to a substrate (1) provided with a metal film (2), the metal film (2) is provided with an asymmetric slit, the slit comprises a small slot (6) and a large slot (7), the side of one side of the small slot (6) and the side of the same side of the large slot (7) are aligned, the small slot (6) and the large slot (7) are rectangular slots, the small slot (6) is provided with optical medium 1, the large slot (7) is provided with electrically controlled birefringent material, the top surface of the metal film (2) is provided with optical medium 2, the optical medium 2 covers the top surface of the metal film (2), the electrically controlled birefringent material is applied with an external voltage, the excitation incident light (8) is normally incident into the tunable surface plasmon excitation structure in the direction from the small slot (6) to the large slot (7), and the transmittance of the excitation incident light (8) relative to the substrate (1) is not 0.

2. The tunable plasmonic excitation structure of claim 1, wherein: The substrate (1) is a glass substrate.

3. The tunable plasmonic excitation structure of claim 1, wherein: The metal film (2) is one of a gold film or a silver film.

4. The tunable plasmonic excitation structure of claim 1, wherein: The optical medium 1 and the optical medium 2 are both PMMA polymers (5).

5. The tunable plasmonic excitation structure of claim 1, wherein: The electrically controlled birefringent material is composed of orientation layers on two sides and a liquid crystal layer (3) in the middle, and the liquid crystal layer (3) is in an electric field formed by the external voltage.

6. A tunable plasmonic excitation structure according to claim 5, wherein: The orientation layer is a polyimide orientation layer (4).

7. The tunable plasmonic excitation structure of claim 5, wherein: The metal film (2) on the two sides of the slit is isolated and disconnected, and the external voltage is arranged on the metal film (2) on the two sides of the slit.

8. The tunable plasmonic excitation structure of claim 1, wherein: The excitation incident light (8) is linearly polarized light with a wavelength of 700 nm, and the polarization direction is perpendicular to the slit direction.

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