CN209590317U - A long focus blazed negative refraction grating lens - Google Patents

Abstract

The utility model discloses a kind of long focusing glittering type negative refraction grating lens, the lens include negative refraction grating and glittering ladder, the concentric ring ladder that the negative refraction grating is equal by height, radius is gradually incremented by from inside to outside forms, and the glittering ladder is made of the annular cone for being located at the concentric ring stepped surfaces；The utility model structure simply easily designs, material obtain be easy, when light from bottom vertically into structure when, structure exit surface occur diffraction, light is effectively focused on to default focal point, luminous energy is effectively utilized, have extremely strong focusing effect.

Description

A long focus blazed negative refraction grating lens

technical field

The utility model relates to a long-focus blazed negative refraction grating lens, which belongs to the technical field of artificial microstructure material integrated optics.

Background technique

With the development of scientific processing technology, it is now possible to process materials as small as nanometers, and these materials have many special effects that they do not have at the macro scale, such as quantum size effects, small size effects, surface and Therefore, it has broad application prospects in the fields of communication, biomedicine, sensing and storage. Artificial microstructured materials refer to the structural design and integration of materials in the micro-nano scale range to achieve flexible control of electromagnetic waves and obtain some novel optical properties.

Compared with scalar beams, vector beams with non-uniform distribution of polarization state contain more abundant physical effects in terms of space-time evolution and interaction with matter. Among them, the polarization state of the cylindrical vector beam (CVB) is cylindrically symmetrically distributed along the axis in space. This unique polarization state distribution characteristics and related physical effects have attracted the research of many researchers. It has important applications in many fields such as molecular imaging, super-resolution microscopy, and micromachining.

With conventional lenses, tight focusing of radially polarized light can be achieved. With the deepening of research, the control methods of CVB are gradually enriched, and the sub-wavelength scale focusing is mostly made of plasmonic lens. Gilad M.Lerman and others experimentally verified the focusing of radially polarized light by plasmonic lens in the article entitled "Demonstration of Nanofocusing by the use of Plasmonic Lens Illuminated with Radially Polarized Light", see NANO LETTERS Volume 9 No. It is recorded on pages 2139-2143 of Issue 5, but plasmons are a coupling mode of evanescent waves, which cannot propagate for a long distance, and can only achieve focusing near the lens surface, and due to the excitation of plasmons The polarization-dependent condition makes its subwavelength focusing for CVB limited to the case of radially polarized light.

In addition, the traditional parabolic mirror makes the beam converge in the same direction through the transformation of the wavefront, and can also focus tightly on the depth of the radially polarized light. On the same side of the mirror, it is difficult to achieve effective application. In 2018, ji xu proposed a design method of negative refraction grating plano-concave lens with controllable focal length, which can perform sub-wavelength tight focusing on radially polarized light and hand-polarized light. Because the focusing effect of this kind of negative refraction plano-concave lens on polarized light is not ideal, a blazed negative refraction grating lens that can enhance the focusing effect is proposed for the structure of this kind of negative refraction grating plano-concave lens.

Utility model content

The purpose of the utility model is to overcome the deficiencies in the prior art and provide a long-focus blazed negative refraction grating lens.

A long-focus blazed negative refraction grating lens, the lens includes a negative refraction grating and a blazed step, the negative refraction grating is composed of concentric ring steps with equal height and gradually increasing radius from inside to outside, and the blazed step is composed of consisting of annular cones on the stepped surface of said concentric rings;

When the radially polarized light is vertically incident into the lens from the bottom, the radially polarized light is diffracted on the surface of each concentric ring step, and the blazing steps can change the diffraction order of the radially polarized light emitted from the step surface , focusing the negative first-order diffracted light to a predetermined focus position, enhancing the utilization efficiency of energy, thereby enabling the lens to achieve sub-wavelength focusing.

Preferably, the step vertex coordinates r _n of the concentric ring steps satisfy; Among them: n ₀ is the refractive index of air, n _eff is the equivalent negative refractive index, z _n is the vertical height nd of the concentric ring step to the bottom, f is the predetermined focus position.

Preferably, the equivalent negative refractive index satisfies n _eff =n _g -λ/d, where n _g is the refractive index of gallium nitride, and its refractive index is 2.67. The equivalent negative refractive index n _eff =- 1.067, where: λ is the focused light wavelength of 562nm, and d is the height of a single layer of concentric ring steps of 150nm.

Preferably, the vertical heights of the annular cones located on the stepped surface of the concentric rings are both d, and the width of the annular cones is equal to the width of the stepped surface, which is equivalent to the difference between the coordinates of the apexes of the adjacent concentric ring steps, and the width w _n satisfies: Among them: n ₀ is the refractive index of air, n _eff is the equivalent negative refractive index, z _n is the vertical height nd of the bottom surface of the concentric ring steps, r _n is the step apex coordinates of the concentric ring steps.

Preferably, the single-layer steps of the concentric ring steps and the ring cone form a structural unit of the negative refraction grating, and the total number N of units is 30.

Preferably, the half-width of the cone bottom of the ring-shaped cone satisfies w _n =rn-rn-r _{n -1} , where r _n is the coordinates of the apex of the concentric ring steps.

Compared with the prior art, the utility model has the beneficial effects: the structure of the utility model is simple and easy to design, and the material is easy to obtain. When the light enters the structure vertically from the bottom, diffraction occurs on the exit surface of the structure, and the light is effectively focused on the The preset focal point effectively utilizes the light energy and has a strong focusing effect. The utility model describes a field focusing device which has certain application value in the fields of super-resolution microscopy, micro-nano processing and optical tweezers.

Description of drawings

Fig. 1 is the sectional structure schematic diagram of the present utility model;

Fig. 2 is the spatial structure schematic diagram of the utility model annular cone;

Fig. 3 is the electric field contour distribution diagram of the focusing simulation result of the radially polarized light by the plano-concave mirror when the preset focal length of the negative refraction grating concave lens is f=7 μm;

Fig. 4 is the electric field modulus square energy distribution curve along the z axis when the plano-concave mirror focuses on radially polarized light when the preset focal length of the negative refraction grating concave lens is f=7 μm;

Fig. 5 is the electric field contour distribution diagram of the focusing simulation result of the radially polarized light by the plano-concave mirror when the preset focal length of the blazed negative refraction grating concave lens is f=7 μm;

Fig. 6 is the electric field modulus square energy distribution curve along the z axis when the plano-concave mirror focuses on radially polarized light when the preset focal length of the blazed negative refraction grating concave lens is f=7 μm;

Fig. 7 is a comparison curve of electric field modulus square energy distribution along the z-axis when the plano-concave mirror focuses on radially polarized light at a preset focal length f=7 μm between a general negative refraction grating concave lens and a blazed negative refraction grating concave lens.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is further described. The following examples are only used to illustrate the technical solution of the utility model more clearly, but not to limit the protection scope of the utility model.

It should be noted that, in the description of the present utility model, the terms "front", "rear", "left", "right", "upper", "lower", "inner", "outer" and the like indicate directions or The positional relationship is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the utility model and does not require the utility model to be constructed and operated in a specific orientation, so it should not be construed as a limitation of the utility model. The terms "front", "rear", "left", "right", "upper" and "lower" used in the description of the utility model refer to the directions in the drawings, and the terms "inner" and "outer" refer to is the direction towards or away from the geometric center of a particular part.

As shown in Figure 1-7, a long-focus blazed negative refraction grating lens, the lens includes a negative refraction grating and a blazed step, and the negative refraction grating is composed of concentric ring steps with equal height and gradually increasing radius from inside to outside 1, the shining step is composed of an annular cone 2 arranged on the surface of the concentric ring step 1;

When the radially polarized light is vertically incident into the lens from the bottom, the radially polarized light is diffracted on the surface of each concentric ring step 1, and the blazing steps can change the diffraction order of the radially polarized light emitted from the step surface Second, the negative first-order diffracted light is focused to a predetermined focus position, and the energy utilization efficiency is enhanced, so that the lens can achieve sub-wavelength focusing.

In this embodiment, the step vertex coordinates r _n of the concentric ring steps satisfy; Among them: n ₀ is the refractive index of air, n _eff is the equivalent negative refractive index, z _n is the vertical height nd of the bottom surface of the concentric ring steps, f is the predetermined focus position, specifically, the negative refraction grating lens, its equivalent negative The refractive index satisfies n _eff = n _g -λ/d _⊥ , where n _g is the refractive index of gallium nitride 2.67, the incident light wavelength λ is the incident light wavelength and its value is 562nm, and d _⊥ is the single-layer height of the concentric ring step 1 150, so its equivalent negative refractive rate is n _eff =-1.067. The coordinate position r _n of the apex of each concentric ring step 1 is determined by the following formula, wherein the relationship between z _n and n is z ₁ =d _⊥ , z ₂ =2d _⊥ , z ₃ =3d _⊥ ,..., z _n = nd _⊥ , each z _n has a corresponding r _n :

Among them, n ₀ is the refractive index of air, n _eff is the equivalent negative refractive index, z _n represents the total height of the nth layer grating, and z _n =nd _⊥ , n is a positive integer greater than 0 and less than or equal to 30, and n _eff is the equivalent The value of the negative refractive rate is -1.067, and f is the predetermined focus position, which is 7 μm here.

The one-to-one correspondence between r and z calculated by using the equivalent negative refractive index combined with Fermat's principle, the specific parameters are given in Table 1.

Table 1. Concave topography data of negative refraction grating lens (unit: μm)

Using the plano-concave lens structure obtained in Table 1, the contour distribution of the focusing electric field for radially polarized light E _r =1V/M is shown in FIG. 3 . Fig. 4 is the electric field modulus square energy distribution curve of the radially polarized light focused by the negative refraction grating concave lens designed with this structural parameter along the z-axis at 5 μm-9 μm, where the ordinate represents the electric field energy, and the abscissa represents the z-axis.

In this embodiment, the equivalent negative refractive index satisfies n _eff =n _g -λ/d _⊥ , where n _g is the refractive index of gallium nitride, and its refractive index is 2.67. The equivalent negative refractive index is obtained by calculation n _eff =-1.067, where: λ is the focused light wavelength of 562nm, d is the single-layer height of the concentric ring step 1 is 150nm, and the specific parameters of the ring cone 2 are given in Table 2.

Table 2 Annular cone structure data (unit is μm)

Using the blazed negative refraction grating concave lens structure constructed on the surface of the negative refraction grating concave lens in Table 2, the distribution of the focusing electric field contours for radially polarized light E _r =1V/M is shown in Figure 5, and it can be observed from the figure that , after adding the annular cone 2 structure, the contour lines near the focal point are denser, and the focusing effect is enhanced.

In this embodiment, the vertical heights of the annular cones 2 on the surface of the concentric ring steps 1 are all d, as shown in Figure 1, viewed from the cross section, the annular cones 2 are on the surface of the concentric ring steps 1 at each level It forms a right-angled triangle, and its right-angled side is parallel to the vertical surface of the concentric ring ladder 1 of this level. The ring-shaped cone 2 is a rotating body structure obtained by rotating a right-angled triangle around its center parallel to the right-angled side. The ring-shaped cone 2 The width is equal to the width of the step surface, which is equivalent to the difference between the coordinates of the vertices of adjacent concentric ring steps 1, and its width w _n satisfies: Among them: n ₀ is the refractive index of air, n _eff is the equivalent negative refractive index, z _n is the vertical height nd of the bottom of the concentric ring step, r _n is the step apex coordinates of the concentric ring step 1.

In this embodiment, the single-layer step of the concentric ring step 1 and the annular cone 2 form a structural unit of the negative refraction grating, the total number of units N is 30, and the half-width of the cone bottom of the annular cone 2 satisfies w _n = r _n -r _n-1 , where, r _n is the apex coordinates of step 1 of the concentric ring steps, and Fig. 6 shows the focusing of radially polarized light by the blazed negative refraction grating concave lens designed with this structural parameter along the z-axis 5 μm- Electric field modulus square energy distribution curve at 9 μm, where the ordinate represents the electric field energy, and the abscissa represents the z-axis.

Fig. 7 is a comparison diagram of the focusing effect of the structure after the construction of the annular cone and before the construction, where the ordinate represents the electric field energy, and the abscissa represents the z-axis. It can be observed that the focusing effect of the structure after the construction of the annular cone is significantly enhanced. At the predetermined 7 μm focus, the electric field energy is enhanced by about 3 times. In a limited space scale, the field space focusing achieves stronger focusing performance. This structure has strong application value in the fields of super-resolution microscopy, micro-nano processing and optical tweezers.

The above is only the preferred embodiment of the utility model, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the utility model, some improvements and deformations can also be made. And deformation should also be regarded as the protection scope of the present utility model.

Claims (6)

1. a kind of long focusing glittering type negative refraction grating lens, which is characterized in that the lens include negative refraction grating and glittering Ladder, the concentric ring ladder that the negative refraction grating is equal by height, radius is gradually incremented by from inside to outside form, the glittering rank Ladder is made of the annular cone for being located at the concentric ring stepped surfaces；

When radial polarisation light impinges perpendicularly on the lens interior from bottom, radial polarisation light is in every level-one concentric ring ladder Diffraction occurs for surface, and the glittering ladder can change the diffraction time of the radial polarisation light of stepped surfaces outgoing, make negative one grade Diffraction light focuses on scheduled focal position, enhances the utilization efficiency of energy, so that the lens be made to realize sub-wavelength dimensions It focuses.

2. long focusing glittering type negative refraction grating lens according to claim 1, which is characterized in that the concentric ring ladder Ladder apex coordinate r_nMeet；Wherein: n₀For air refraction, n_eff For equivalent negative index, z_nIt is scheduled focal position for the vertical height nd, f of concentric ring ladder to bottom surface.

3. long focusing glittering type negative refraction grating lens according to claim 2, which is characterized in that the equivalent negative refraction Rate meets n_eff=n_g- λ/d, n_gFor the refractive index of gallium nitride, refractive index 2.67, by the way that equivalent negative index is calculated n_eff=-1.067, in which: λ is that the optical wavelength 562nm, d focused is concentric ring ladder single layer height 150nm.

4. long focusing glittering type negative refraction grating lens according to claim 1, which is characterized in that be located at the concentric ring The vertical height of the annular cone of stepped surfaces is d, and annular cone width is equal with stepped surfaces width, is equivalent to neighboring concentric ring The difference of the coordinate on ladder vertex, width w_nMeet:Wherein: n₀For air refraction, n_effFor equivalent negative index, z_nFor the vertical height nd, r of ladder to bottom surface_nFor the rank of concentric ring ladder Terraced apex coordinate.

5. long focusing glittering type negative refraction grating lens according to claim 1, which is characterized in that the concentric ring ladder Single layer ladder and annular cone composition negative refraction grating a structural unit, total unit number N be 30.

6. long focusing glittering type negative refraction grating lens according to claim 1, which is characterized in that the cone of the annular cone Bottom half width meets w_n=r_n-r_n-1, wherein r_nFor the ladder apex coordinate of concentric ring ladder.