CN105467517B

CN105467517B - Surface plasma waveguide based on ultra-strong light constraint of sub-wavelength metal V groove

Info

Publication number: CN105467517B
Application number: CN201511003478.0A
Authority: CN
Inventors: 马云燕; 马佑桥; 艾华; 束鑫
Original assignee: Xuzhou Tiancheng Intelligent Technology Co ltd
Current assignee: Xuzhou Tiancheng Intelligent Technology Co.,Ltd.
Priority date: 2015-12-24
Filing date: 2015-12-24
Publication date: 2020-11-27
Anticipated expiration: 2035-12-24
Also published as: CN105467517A

Abstract

A surface plasma waveguide based on sub-wavelength metal V-groove ultra-strong light constraint mainly comprises: a metal (silver is selected as a material) substrate 1 engraved with a V-shaped groove, two inner walls of the V-shaped groove on the silver substrate 1 are plated with a layer of silicon dioxide dielectric film 2, and the whole optical waveguide is surrounded by an air layer 3; width W on the V-groove, thickness t of silicon dioxide film at the tip of the V-groove, angle alpha and angle theta of the V-groove.

Description

Surface plasma waveguide based on ultra-strong light constraint of sub-wavelength metal V groove

Technical Field

The invention relates to a nano optical waveguide device, in particular to a surface plasma waveguide based on ultra-strong light constraint of a sub-wavelength metal V groove.

Background

Due to the limitation of optical diffraction limit, the development of small integration of the conventional dielectric optical waveguide has encountered insurmountable technical bottleneck. The research on how to break through the waveguide of the optical diffraction limit has extremely important research significance for nano-integrated optics and quantum optical communication.

In recent years, researchers have found that the presence of a propagating electromagnetic wave, i.e., a surface plasmon wave, at the interface between a conductor and a dielectric can significantly break through the optical diffraction limit and confine the electromagnetic wave in the nanometer range. Therefore, the sub-wavelength optical waveguide based on surface plasmon has also received great attention from the scientists. The surface plasmon wave is a surface evanescent wave generated by oscillating and coupling an electromagnetic wave with free electrons on the surface of a conductor. In addition to the advantage of breaking the diffraction limit of light, another significant advantage of surface plasmons is their locally enhanced electromagnetic field energy distribution. The enhanced local electromagnetic field can obviously accelerate the interaction between light and substances, and has extremely important application prospects for biosensing, surface-enhanced Raman scattering, nano lithography and the like. However, the carrier for generating surface plasmon is free electrons of the surface resonance of the conductor, and thus, metal ohmic loss is an inevitable problem of surface plasmon. More importantly, under the condition of realizing super-strong optical beam-binding, the transmission (ohmic) loss of the surface plasma optical waveguide is further increased, so that the practical application of the surface plasma optical waveguide is restricted. The research on how to simultaneously realize low loss and nano-optical confinement is an important problem to be solved urgently by the surface plasmon waveguide.

Disclosure of Invention

The invention provides a sub-wavelength surface plasma waveguide based on metal V-groove ultra-strong light constraint, and mainly provides a method for realizing ultra-strong light constraint by evaporating a layer of high-refractive-index material on the surface of a V-groove.

The technical scheme of the invention comprises the following implementation steps:

in accordance with the above purpose, we have utilized the beam-tying effect of a metallic V-groove to design a sub-wavelength optical waveguide. The surface plasmon waveguide mainly includes: the optical waveguide comprises a metal (silver is selected as a material) substrate 1 engraved with a V-shaped groove, two inner walls of the V-shaped groove on the silver substrate 1 are plated with a layer of silicon dioxide dielectric film 2, and the whole optical waveguide is surrounded by an air layer 3.

The metal material in the invention is selected from common noble metal silver: compared with other noble metals, the material silver has a smaller imaginary part of dielectric constant in a near infrared spectrum, so that the material silver has smaller optical transmission loss.

The invention relates to a nano optical processing and optical coating technology, which comprises the following steps: the preparation of the metal V groove can adopt a focused ion beam etching process; the film formation of the silicon dioxide can adopt vacuum evaporation, ion sputtering or vacuum electron beam sputtering film formation processes. The thickness of the silicon dioxide film needs to be controlled during the film coating process, namely the silicon dioxide film gradually becomes thicker from top to bottom.

The transmission performance of the optical waveguide in the invention greatly depends on the design of the structural parameters of the optical waveguide: the width W on the vee, the vee tip silica film thickness t, the vee angle α and θ, as shown in fig. 1.

In the invention, V-groove angles alpha and theta are selected as follows: under the communication wavelength of 1550 nanometers, in order to ensure that the realization of the sub-wavelength optical confinement and the lower optical transmission loss is realized, alpha and theta are acute angles, the optimized angles are within 40-50 degrees, and the angle theta is larger than alpha.

The selection of the width W on the V-shaped groove is as follows: at the communication wavelength of 1550 nm, in order to ensure the realization of sub-wavelength optical confinement and lower optical transmission loss, the optimized W value must be larger than 0.8 μm. Meanwhile, the W value is less than 1.55 microns under the principle of considering the constraint of satisfying the sub-wavelength.

The invention relates to a method for selecting the thickness t of silicon dioxide film at the tip of a V-shaped groove, which comprises the following steps: under the communication wavelength of 1550 nanometers, in order to ensure that the realization of the sub-wavelength optical confinement and the lower optical transmission loss is realized, the optimized t value is within 5 nanometers to 300 nanometers.

Drawings

FIG. 1 is a schematic diagram of the cross-sectional structure of a sub-wavelength metal V-groove based ultra-strong light confinement surface plasmon polariton.

FIG. 2 is a schematic view of a process for preparing the surface plasmon waveguide of the present invention.

FIG. 3 is a schematic view of the surface plasmon waveguide optical field distribution of the present invention.

FIG. 4 is a diagram showing the optical field distribution of a conventional metal V-groove surface plasmon waveguide in accordance with the present invention.

Detailed Description

Embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in fig. 1, the subwavelength metal V-groove based ultra-strong light confinement surface plasmon waveguide comprises: the metal (the material is selected from silver) substrate 1 carved with V groove, silicon dioxide dielectric film 2 is evaporated on two inner walls of the V groove, the thickness of the silicon dioxide dielectric film is gradually thickened from top to bottom, the whole optical waveguide is placed in air 3, namely the air is regarded as the cladding of the optical waveguide.

As shown in fig. 2, a schematic diagram of a process for preparing a surface plasmon waveguide based on ultra-strong light confinement of a subwavelength metal V-groove: 1, etching a metal V groove on a metal substrate 1 by utilizing a focused ion beam process; 2, plating a layer of polymethyl methacrylate (PMMA) film on the metal substrate 1 engraved with the V groove by using a plating process, wherein the thickness of the PMMA film has no influence on the performance of the surface plasma waveguide; 3, removing the PMMA film on the inner wall of the V-shaped groove by utilizing a photoetching exposure development technology; 4, plating a layer of silicon dioxide film on the whole substrate by using a film plating process; and 5, placing the whole optical waveguide in an acetone solution until PMMA on two sides of the V groove is dissolved, namely silicon dioxide on two sides of the V groove is stripped.

Example 1: in this embodiment, the width W of the V-groove is 1 μm, the angles α and θ of the V-groove are 40 degrees and 45 degrees, respectively, and the thickness of the silicon dioxide thin film layer gradually increases from zero to 5 nm. The working wavelength is selected from the communication wavelength, namely the wavelength is 1550 nanometers, under the communication wavelength, the dielectric constant of the material silver is-129 +3.3i, the dielectric constant of the material silicon dioxide is 2.25, and the dielectric constant of air is 1.

Before discussing the transmission performance of surface plasmon waveguides, let us first define two evaluation parameters: transmission length L and mode area S. The transmission length is used to describe the loss characteristics of the waveguide, with longer transmission lengths indicating less optical loss. The mode area is used to define the optical confinement capability of the waveguide, and smaller mode areas indicate greater local confinement capability of the light. The transmission length and the mode area are respectively expressed as:

L＝λ/(4πIm(n_eff))

S＝4S_eff/λ²

wherein λ represents the wavelength of the incident light, Im (n)_eff) Is the equivalent refractive index n_effImaginary part of, S_effIs the equivalent mode area and;

S_eff＝W_m/max[W(x，y)]

wherein, W_mAnd W (x, y) represent total electromagnetic energy and energy density, respectively.

Referring to fig. 3, the surface plasmon waveguide optical field profile of the present invention is shown, and the structural parameters are described with reference to example 1. Fig. 4 is a schematic daughter optical waveguide of the optical field distribution of the conventional metal V-groove surface plasmon waveguide of the present invention.

Obviously, compared with the traditional metal V-groove surface plasmon waveguide, the improved surface plasmon waveguide has stronger optical field confinement capability. For example, the mode area of the surface plasmon waveguide of the present invention is equal to S ═ λ²1760, and the area of the conventional metal V-groove surface plasma waveguide is equal to S ═ lambda²And 43, the light beam binding capacity of the surface plasma waveguide is improved by nearly 40 times compared with that of the traditional V-groove surface plasma waveguide. The stronger optical local confinement means that more optical field will be distributed near the metal surface, i.e. the mode loss will be larger, i.e. the mode transmission length will be smaller. However, it is worth mentioning thatIn the conventional V-groove surface plasmon waveguide, although the waveguide of the present invention can greatly improve the optical local confinement capability, the propagation length of the mode is reduced by only 8 times. If the quality factor is defined as L/S²The quality factor of the surface plasma waveguide is improved by nearly 200 times, the sub-wavelength light guiding advantage of the surface plasma waveguide is fully embodied, and the integration miniaturization of a photon loop and a device is facilitated.

The above-described embodiments are merely illustrative of the present invention and are not intended to limit the present invention. The invention may be embodied in other forms not specifically described herein. All technical solutions formed by adopting equivalent substitution or transformation belong to the protection scope claimed by the invention.

Claims

1. A sub-wavelength metal V-groove ultra-strong light confinement based surface plasmon waveguide, comprising: the plasma waveguide structure comprises a silver substrate (1) engraved with a V-shaped groove, wherein two inner walls of the V-shaped groove on the silver substrate (1) are plated with a layer of silicon dioxide dielectric film (2), and the whole surface plasma waveguide is surrounded by an air layer (3); the upper width W of the V-shaped groove, the thickness t of the silicon dioxide film at the tip of the V-shaped groove, and the angles alpha and theta of the V-shaped groove;

under the condition of a communication wavelength of 1550 nanometers, in order to ensure that the restraint of sub-wavelength light and lower light transmission loss are realized, both alpha and theta are acute angles, the angles are within 40-50 degrees, and the angle theta is larger than alpha;

the preparation process of the sub-wavelength metal V groove comprises the following steps: a, etching a metal V groove on a silver substrate (1) by utilizing a focused ion beam process; b, plating a polymethyl methacrylate (PMMA) film on the silver substrate (1) engraved with the V groove by using a plating process; c, removing the PMMA film on the inner wall of the V groove by utilizing a photoetching exposure development technology; d, plating a layer of silicon dioxide film on the whole substrate by using a film plating process; e, placing the whole surface plasma waveguide in an acetone solution until PMMA on two sides of the V-shaped groove is dissolved;

under the condition of a communication wavelength of 1550 nanometers, in order to ensure that the restraint of sub-wavelength light and lower optical transmission loss are realized, the W value is required to be more than 0.8 micrometer; meanwhile, the W value is less than 1.55 microns under the principle of considering the constraint of satisfying the sub-wavelength.

2. The subwavelength metal V-groove ultra-strong light confinement based surface plasmon waveguide of claim 1, wherein: at a communication wavelength of 1550 nm, t is within 5 nm to 300 nm to ensure sub-wavelength optical confinement and low optical transmission loss.

3. The surface plasma waveguide based on the ultra-strong light constraint of the sub-wavelength metal V-groove according to claim 1, which relates to the nano-optical processing and optical coating technology, and is characterized in that: the preparation of the metal V groove can adopt a focused ion beam etching process; vacuum evaporation, ion sputtering or vacuum electron beam sputtering film forming process is adopted for the film forming of the silicon dioxide; the thickness of the silicon dioxide film needs to be controlled during the film coating process, namely the silicon dioxide film gradually becomes thicker from top to bottom.