CN113391384B - On-chip directional rectification super surface based on cascade nano microstructure and design method thereof - Google Patents

Abstract

The invention discloses an on-chip directional rectification super surface based on a cascade nano microstructure and a design method thereof, wherein the on-chip super surface with the directional rectification function can realize the rectification of surface waves with a plurality of incidence angles (within +/-20 degrees), so that the surface waves are transmitted and propagated along the normal direction (0 degree), and the performance similar to a zero-refractive-index material is formed. The on-chip rectification super surface is composed of a silver substrate layer, a silicon dioxide waveguide layer, a semi-elliptical silver nanostructure layer and an isosceles trapezoid silver nanostructure layer, and surface plasmon resonance generated by interaction of the semi-elliptical structure and the isosceles trapezoid silver nanostructure layer and induced phase gradient thereof realize control on surface waves. The specific method for designing the on-chip rectification super surface comprises the following steps: meanwhile, the size of the semi-elliptical structure, the size of the big side and the small side of the isosceles trapezoid structure and the distance between the semi-elliptical layer and the isosceles trapezoid layer are optimized, so that the rectification function is realized under the condition of the largest possible oblique incidence angle.

Description

On-chip directional rectification super surface based on cascade nano microstructure and design method thereof

Technical Field

The invention belongs to the technical field of micro-nano optics, and particularly relates to an on-chip directional rectification super surface based on a cascade nano microstructure and a design method thereof.

Background

In recent years, there has been increasing interest in a super-surface, i.e., an on-chip (2D) super-surface, that can manipulate light in a new degree of freedom. The on-chip two-dimensional meta-surface creates a new degree of freedom for optical manipulation that can easily perform many functions that are difficult to achieve in complex three-dimensional (3D) meta-surfaces. Recent developments and advances in the interaction of light with two-dimensional cell surfaces on-chip can realize many novel on-chip functions and applications, including on-chip superlenses, on-chip beam steering, mode multiplexing, demultiplexing, mode converters, Airy beams, no diffraction propagation, and the like. By utilizing the spatial change of phase shift caused by the sub-wavelength nano antenna array, the two-dimensional super surface can modulate the shape and the direction of the wave surface on the chip, and finally, the optical manipulation in any plane is realized.

Light rectification, which is a long-standing challenge in the field of optical turning, refers to the manipulation and combination of light beams with multiple directional oscillators in the same output direction, which is difficult to achieve based on conventional optics. To our knowledge, on-chip hypersurfaces with such beam-rectifying function have not been studied or demonstrated, since it is rather difficult to manipulate a plurality of different incident wave vectors and to exit them with the same exiting wave vector. Typical light rectifying devices utilize partially reflective/transmissive mirrors that combine two orthogonally propagating waves, but at a cost of at least 50% of the light energy. The zero-refractive-index material can realize the function that light enters from any angle and exits along one angle, but only supports the modulation of light in an infrared band at present. The on-chip optical directional rectification super-surface can rectify incident surface waves with different angles in a visible light wave band, and a phenomenon similar to zero refractive index is realized. The on-chip photonic device is easy to manufacture, good in compatibility and high in integration level.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides an on-chip directional rectification super surface based on a cascade nano microstructure and a design method thereof. The on-chip directional rectification technology realizes that surface waves obliquely incident within +/-20 degrees are emitted along 0 degree and can work under the bandwidth of 60 nm.

In order to achieve the purpose, the technical scheme of the invention is as follows:

in a first aspect, the invention provides an on-chip directional rectification super surface based on a cascade nano-microstructure, which is characterized in that:

it is composed of four structures: the device comprises a metal substrate layer, a dielectric waveguide layer, a rectifying layer consisting of a row of semi-elliptical metal micro-nano structures and a row of isosceles trapezoid metal micro-nano structures;

the array of semielliptical metal micro-nano structures is used for rectifying plane waves for the first time, and the incident direction of the plane waves is perpendicular to the long axis direction of a semiellipse;

every two trapezoids of the array of the trapezoid metal micro-nano structures are used as a rectifying unit, the large sides of the two trapezoids are connected and symmetrical along the large sides, and the array of the trapezoid metal micro-nano structures are subjected to secondary rectification by plane waves.

The metal substrate layer, the dielectric waveguide layer and the two metal micro-nano structure layers are sequentially arranged.

Preferably, the metal substrate is a silver substrate.

Further, the dielectric waveguide is a silica waveguide.

Furthermore, the two rows of metal semi-elliptical and metal isosceles trapezoid rectifying micro-nano structures are silver nano structures.

In a second aspect, the present invention provides a method for designing the above-mentioned on-chip directional rectifying super surface based on the cascade nano microstructure, which is characterized in that: the method comprises the following steps:

s1: determining the major and minor axis size working wavelength of the semi-elliptical microstructure, and focusing the surface wave under the wavelength in the major axis range after oblique incidence in the range of +/-20 degrees;

s2: and simultaneously, the distance between the two rows of microstructures and the size of the big and small sides of the second row of isosceles trapezoid microstructures are optimized to meet the phase gradient emitted along the normal direction.

The on-chip optical rectification super-surface in the invention is composed of four structures: the metal substrate layer, the dielectric waveguide layer, the rectifying layer consisting of a row of semielliptical metal micro-nano structures and a row of isosceles trapezoid metal micro-nano structures, the metal substrate layer, the dielectric waveguide layer and the two rows of metal micro-nano structure layers are sequentially arranged; the metal bottom layer, the dielectric waveguide layer and the metal micro-nano structure are respectively a silver substrate, a silicon dioxide waveguide and a silver microstructure; the action mode of the semi-elliptical structure and the surface wave is that the surface wave is incident perpendicular to the long axis; the action mode of the trapezoid structure and the surface wave is that the surface wave acted by the semi-elliptic structure interacts with the isosceles trapezoid structure along the direction parallel to the big side of the isosceles trapezoid.

The application of the on-chip super-surface with directional rectification in the invention is as follows: the wave zone plate with the filtering function is used for realizing the rectification of the multi-angle surface wave to realize the effect similar to a zero refractive index.

Compared with the traditional light rectifying device and the on-chip light steering device, the invention has the following advantages and beneficial effects:

(1) oblique incident surface waves with incidence angles ranging +/-20 deg. can be made to propagate along the 0 deg. direction within the visible wavelength of around 500nm by the plasmon interaction between the two cascaded on-chip nanostructures.

(2) This on-chip super-surface scheme enables coherent coupling, cascading and alignment between multiple on-chip nanostructure layers with only one lithography process, as compared to the multi-layer fabrication and alignment difficulties of conventional super-surfaces.

(3) The multi-angle directional rectification on the chip designed by the invention can keep the directional rectification function within the bandwidth of 60nm, and the super surface plays an important role in the mode multiplexing/demultiplexing of the optical mode on the chip, the multi-channel information hybrid processing and the like.

Drawings

FIG. 1 is a schematic top view of a super-surface structure with directional rectification in accordance with the present invention;

FIG. 2 is a schematic side view of a super-surface structure with directional rectification in accordance with the present invention;

FIG. 3 is a graph showing the effect of rectification simulation of a 500nm surface wave incident at 10 ° with only a semi-elliptical structure;

FIG. 4 is a graph showing the effect of rectification simulation under the action of an isosceles trapezoid structure when a 500nm surface wave is incident at 10 °;

FIG. 5 is a graph showing the effect of rectification simulation under the combined action of a semi-elliptical structure and an isosceles trapezoid structure when a 500nm surface wave is incident at 10 degrees;

FIG. 6 is a graph of the rectification simulation effect of the 500nm surface wave under the combined action of the semi-elliptical and isosceles trapezoidal structures when the surface wave is incident at 0, 10, 15 and 20 degrees;

FIG. 7 is a graph showing the effect of rectification simulation of a 500nm surface wave incident at 20 ° at four different wavelengths, 440nm,500nm,560nm, and 620nm, respectively.

In the figure: r is₁A minor axis that is a semi-elliptical configuration; r is₂A major axis of a semi-elliptical configuration; w is a₁Is equal toThe short side of the waist-shaped structure; w is a₂Is the long side of the isosceles trapezoid structure; h is the height of an isosceles trapezoid structure; t is t₁The thickness of the top layer semi-elliptical and isosceles trapezoid nano microstructure; t is t₂Is SiO as an intermediate layer₂The thickness of (a); t is t₃Is the thickness of the underlying silver.

Detailed Description

In order to more clearly explain the structure and the functions of the present invention, the following detailed description of the present invention is provided in conjunction with the accompanying drawings.

Example 1

The embodiment is a specific design process of an on-chip optical directional rectification super-surface.

As an example, it is first determined that the rectifying super-surface is an on-chip super-surface, as shown in fig. 1-2, a semi-elliptical silver structure is used as a first layer of the rectifying structure, an isosceles trapezoid silver structure is used as a second layer of the rectifying structure, silicon dioxide is used as an optical waveguide for transmitting a light source in a visible light band, and a silver base layer is used for ensuring that light does not leak in the-z direction when the light is transmitted in the visible light waveguide. The first layer of semi-elliptical silver structure with a period of 3.2 μm can focus surface waves incident at different angles on a sheet at a wavelength of 500nm, wherein fig. 3 represents the wave front shaping of the surface waves by the semi-elliptical silver structure. And each two isosceles trapezoid silver structures of the second layer are taken as a unit, the large side is opposite to the large side, and the large period is 3.2 micrometers, wherein the isosceles trapezoid silver structures of one large unit shape the wave front of the surface wave. Fig. 5 represents the rectification of the surface wave under the combined action of a semi-elliptical silver structure and an isosceles trapezoid silver structure. Optimized simulation is carried out on the distance between the semi-elliptical silver structure and the isosceles trapezoid silver structure by utilizing electromagnetic simulation software FDTD Solutions, after the distance between the semi-elliptical silver structure and the isosceles trapezoid silver structure is 2.5 micrometers (the distance between the semi-elliptical long axis and the isosceles trapezoid center), the angle rectification range of the on-chip rectification device can be determined by scanning the incident angle at the wavelength of 500nm, as shown in figure 6. The 500nm to 560nm operating bandwidth of such an on-chip rectifying device can be determined by scanning the operating wavelength at an incident angle of 20 deg., as shown in fig. 7, below 500nm or above 560nm, such an on-chip rectifying device can no longer function as a rectifier.

Claims (6)

1. An on-chip directional rectification super surface based on a cascade nano microstructure is characterized in that:

it is composed of four structures: the device comprises a metal substrate layer, a dielectric waveguide layer, a rectifying layer consisting of a row of semi-elliptical metal micro-nano structures and a row of isosceles trapezoid micro-nano structures;

the array of semielliptical metal micro-nano structures is used for rectifying plane waves for the first time, and the incident direction of the plane waves is perpendicular to the long axis direction of a semiellipse;

each two trapezoids of the isosceles trapezoid micro-nano structure line are used as a rectifying unit, the large sides of the two trapezoids are connected and symmetrical along the large side, and the isosceles trapezoid micro-nano structure line is subjected to secondary rectification by plane waves;

the metal substrate layer, the dielectric waveguide layer and the two metal micro-nano structure layers are sequentially arranged.

2. The cascade nano-microstructure-based on-chip directionally rectified super-surface of claim 1, wherein: the metal substrate is a silver substrate.

3. The cascade nano-microstructure based on-chip directionally rectified super-surface of claim 1 or 2, wherein: the dielectric waveguide is a silica waveguide.

4. The cascade nano-microstructure based on-chip directionally rectified super-surface of claim 1 or 2, wherein: the semi-elliptical metal micro-nano structure and the isosceles trapezoid micro-nano structure are both silver nano structures.

5. The cascaded nano-microstructure based on-chip directionally rectified super surface of claim 3, wherein: the semi-elliptical metal micro-nano structure and the isosceles trapezoid micro-nano structure are both silver nano structures.

6. A method for designing the cascade nano-microstructure based on-chip directionally rectified super-surface as claimed in claim 1, 2 or 5, wherein: the method comprises the following steps:

s1: determining the major and minor axis size working wavelength of the semi-elliptical microstructure, and focusing the surface wave under the wavelength in the major axis range after oblique incidence in the range of +/-20 degrees;

s2: and simultaneously, the distance between the two rows of microstructures and the size of the big and small sides of the second row of isosceles trapezoid microstructures are optimized to meet the phase gradient emitted along the normal direction.

Images