CN112946792A

CN112946792A - Micro lens for realizing bifocal focusing

Info

Publication number: CN112946792A
Application number: CN202110171418.9A
Authority: CN
Inventors: 许吉; 陈牧林; 朱聪颖; 黄浩思; 段俊祥; 张怡宁; 刘宁; 陆云清
Original assignee: Nanjing University of Posts and Telecommunications
Current assignee: Nanjing University of Posts and Telecommunications
Priority date: 2021-02-07
Filing date: 2021-02-07
Publication date: 2021-06-11
Anticipated expiration: 2041-02-07
Also published as: CN112946792B

Abstract

The invention discloses a microlens for realizing double focus focusing, which is characterized by comprising a cylindrical lens made of a uniform medium material, the incident surface of the lens is a plane, and the exit surface of the lens is a concave surface with a stepped grating structure, so the The echelle grating is provided with a first echelle grating region corresponding to a focal length f ₁ and a second echelle grating region corresponding to a focal length f ₂ , where f ₁ <f ₂ ; The focal point corresponding to the echelle grating region is lower than the focal point corresponding to the second echelle grating region, and the interface between the first echelle grating region and the second echelle grating region intersects at one point in the axial direction. The plano-concave lens designed by the present invention can realize dual focus focusing at the same time, and can effectively reduce the dispersion degree of the focal spot and make the focusing more uniform.

Description

Micro lens for realizing bifocal focusing

Technical Field

The invention belongs to the field of bifocal microlenses, and particularly relates to a microlens for realizing bifocal focusing.

Background

The focusing of the lens has wide application prospect in the fields of optical imaging, photoetching and the like. When the grating period is less than the working wavelength, the equivalent negative refractive index can be obtained, the sub-wavelength light beam negative refraction lens designed according to the principle can form excellent focusing effect on radial polarized light, rotary polarized light and generalized cylindrical vector light beams, but the focus diffusion degree of the bifocal focusing lens is large and the energy distribution is uneven, so that the requirements of industrial production cannot be met.

Research shows that in the structure with the bifocal lens, a longer flat step exists at the structure boundary corresponding to the focal length, and light rays emitted by the long step are not refracted and can affect the quality of a focusing field.

Disclosure of Invention

In order to realize bifocal focusing by using the same lens structure and reduce the dispersion degree of bifocal focal spots, so that the bifocal focal spots are more compactly focused and the energy distribution is more uniform, the invention provides a plano-concave micro lens for realizing bifocal focusing.

The technical purpose is achieved, the technical effect is achieved, and the invention is realized through the following technical scheme:

a microlens for realizing bifocal convergence comprises a cylindrical lens made of uniform medium material, wherein the incident surface of the lens is a plane, the emergent surface of the lens is a concave surface with a step-shaped grating structure, and the step-shaped grating is arranged from the incident surface to the emergent surface and comprises a lens with a focal length f corresponding to the focal length f₁And a first step grating zone corresponding to a focal length f₂Wherein f is a second echelle grating region of₁＜f₂(ii) a The focus corresponding to the first echelon grating area is lower than the focus corresponding to the second echelon grating area, and the interface of the first echelon grating area and the second echelon grating area intersects at a point in the axial direction.

As a further improvement of the present invention, the first step grating region includes M steps, and the second step region includes N steps; the step height of the first step grating area is the same as that of the second step area;

the coordinate of the vertex of the vertical edge of the step-shaped grating structure is (r)_i，z_i)，r_iAs a horizontal coordinate variable, z_iIs a longitudinal coordinate variable, i is a step serial number,

wherein: realization of f₁The step coordinates of the first step grating region of the focal length satisfy the following relationship:

z_i＝i·d_⊥；

wherein i belongs to [1, M ]; m belongs to [10, 18 ];

the step coordinates of the second step grating area satisfy the following relation:

z_i＝i·d_⊥；

wherein i belongs to [ M +1, M + N ]; n is an element [10, 18]

As a further improvement of the present invention, the vertical height of the steps in the stepped grating structure satisfies the following relationship:

d_⊥＝λ₀/(n-n_eff)

in the formula: d_⊥Is the vertical height of the step, λ₀Is the working wavelength, n is the refractive index of the dielectric material,n _effis an equivalent negative refractive index.

As a further improvement of the invention, the inner side wall of the step-shaped grating structure is a vertical wall.

As a further improvement of the invention, the method further comprises removing 3 steps at the incident surface end of the first step grating region, and further forming a hollow round hole at the bottom, wherein the height of the hollow round hole is equal to 3d ″.

As a further improvement of the present invention, the focal position of the first echelon grating region is coplanar with the incident surface, and the focal position of the second echelon grating region is coplanar with the bottom end of the first echelon grating region.

As a further improvement of the invention, n is selected to be in the range of 1.0 to 3.0, the equivalent negative refractive index neff of the stepped grating is selected to be in the range of-1.0 to-0.8, and the working wavelength 0 is selected to be in the range of 0.4 μm to 2.0 μm.

As a further improvement of the present invention, said f₁Has a value in the range of 4 to 6 μm, wherein f₂Has a value range of 6 to 9 μm, f₂-f₁The thickness is controlled to be 1-2 μm.

The invention has the beneficial effects that: the plano-concave lens can simultaneously realize bifocal focusing, and through the optimized design, the focal point is more compact, the energy distribution and focusing are more uniform, and the dispersion degree of the focal spot can be effectively reduced.

Drawings

FIG. 1 is a three-dimensional block diagram of one embodiment of a plano-concave microlens design according to the present invention;

FIG. 2 is a schematic diagram illustrating the coordinate relationship of the vertical edge vertices of a plano-concave microlens according to an embodiment of the present invention;

FIG. 3 is a graph of the focusing effect of a bifocal plano-concave microlens of the prior art and of the present invention, (a) a plano-concave microlens of the prior art, (b) a plano-concave microlens of the present invention;

FIG. 4 is a comparison of focal field energy distributions before and after optimization;

FIG. 5 is a schematic diagram showing the relationship between the variation of the positions of the bifocal points before and after optimization, (a) a plano-concave microlens of the prior art, and (b) a plano-concave microlens of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The following detailed description of the principles of the invention is provided in connection with the accompanying drawings.

As shown in fig. 1-2, this embodiment proposes a plano-concave microlens for realizing bifocal focusing, the lens uses a single material as a medium, the concave surface of the exit surface of the microlens is a stepped grating structure, along the exit direction of light, the stepped grating structure is designed to correspond to two grating regions with different focal lengths to realize bifocal focusing, including a lower part corresponding to a focal length f₁And a first step grating zone located above and corresponding to a focal length f₂Wherein f is a second echelle grating region of₁＜f₂. In order to reduce the dispersion degree of a focal spot and enable the focusing to be more uniform, in the design process, a second stepped grating area above the second stepped grating area is lifted upwards, so that a focus corresponding to the first stepped grating area is lower than a focus corresponding to the second stepped grating area, long flat steps on an interface of the first grating area and the second grating area are eliminated, and the interface of the first stepped grating area and the interface of the second stepped grating area are intersected at one point in the axial direction.

In an embodiment of the present invention, the focal length f of the first grating region is preset₁6 μm, the focal length f of the second grating region₂And 8 μm. Correspondingly, the preferred step design count is that 27 grating steps of the emergent concave surface in the designed micro lens can be selected, and the corresponding lower first grating area is provided with 12 steps to realize the preset focal length f₁The upper second grating area is provided with 15 steps to realize the preset focal length f₂Focusing of (3).

In order to enable the focal spot to be more focused and uniform, the part corresponding to the preset focal length of 8 microns is raised by 3 steps, so that the purpose of eliminating the flat long step at the structural interface is achieved, the 3 steps at the bottom of the part corresponding to the preset focal length of 6 microns are removed, and finally, the plano-concave micro lens which is continuous at the grating structure boundary and has the hollow round hole at the bottom and can realize bifocal focusing is formed, so that the height of the hollow round hole at the bottom is equal to the height of 3 gratings.

The structure of the stepped grating according to this embodiment is designed as follows:

(1) the ladder inside wall is vertical wall, and each layer of ladder height homogeneous phase equals, and the ladder height is: d_⊥＝λ₀/(n-n_eff)(1)。

(2) Vertical edge vertex coordinates (r)_i，z_i)，r_iAs a horizontal coordinate variable, z_iIs a longitudinal coordinate variable, and i is a step serial number.

(a) Lower implementation of the focal length f₁The focused vertex coordinates of the vertical edges of the steps meet the following relation:

(b) upper part realizing focal length f₂The focused vertex coordinates of the vertical edges of the steps meet the following relation:

wherein n is_effThe negative refractive index is selected to be in the range of-1.0 to-0.8, in this example n_effCalculated as-0.9, operating wavelength λ₀532nm, the medium refractive index n is 2.36. Calculating the height of the inner vertical wall of the step, d, according to the formula (1)_⊥The abscissa of each step is calculated according to equations (2) and (3) at 163.2nm, and the resulting three-dimensional structure of the plano-concave microlens for achieving bifocal focusing is shown in fig. 1, and the corresponding vertical edge vertex coordinates are shown in fig. 2.

Fig. 3-4 are the simulation of the original plano-concave lens and the optimized lens, respectively, and the comparison shows that the optimized negative refraction plano-concave lens not only eliminates the secondary focus, but also makes the energy distribution of the focus more uniform.

Fig. 5 is a schematic diagram of result optimization before and after the optimization design, in which a part corresponding to a preset focal length of 8 μm is raised by 3 steps, so as to achieve the purpose of eliminating a flat long step at the interface of the structure, and 3 steps at the bottom of the part corresponding to the preset focal length of 6 μm are removed, thereby finally forming a plano-concave microlens for realizing bifocal focusing with a hollow round hole at the bottom.

The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.

Claims

1. A microlens realizing bifocal gathering is characterized in that: comprising a cylindrical lens made of a uniform medium material, the incident surface of the lens is a plane, and the exit surface of the lens is a concave surface with a stepped grating structure, and the stepped The shape grating is provided in the direction from the incident surface to the outgoing surface and includes a first echelle grating area corresponding to the focal length f ₁ and a second chequer grating area corresponding to the focal length f ₂ , where f ₁ <f ₂ ; the first echelle grating The focal point corresponding to the region is lower than the focal point corresponding to the second echelle grating region, and the interface between the first echelle grating region and the second echelle grating region intersects at one point in the axial direction.

2 . The microlens according to claim 1 , wherein the first echelon grating area includes M steps, the second step area includes N steps; the first step grating area includes N steps; 3 . The step height of the echelle grating area is the same as the step height of the second step area;

The coordinates of the vertical side vertexes of the stepped grating structure are (ri, _zi ₎ , ri is a horizontal coordinate variable, _zi is a vertical coordinate variable, and _i is a step sequence number,

Wherein: the step coordinates of the first echelon grating region that realizes the f ₁ focal length satisfy the following relationship:

z _i =i·d _⊥ ;

where i∈[1, M]; M∈[10, 18];

The step coordinates of the second echelon grating area satisfy the following relationship:

z _i =i·d _⊥ ;

where i∈[M+1, M+N]; N∈[10, 18]

3. The microlens according to claim 2, wherein the vertical height of the steps in the stepped grating structure satisfies the following relationship:

d _⊥ =λ ₀ /(nn _eff )

In the formula: d _⊥ is the vertical height of the step, λ ₀ is the working wavelength, n is the refractive index of the medium material, and n _eff is the equivalent negative refractive index.

4 . The microlens of claim 3 , wherein the inner side walls of the steps of the step-shaped grating structure are vertical walls. 5 .

5 . The microlens according to claim 2 , further comprising removing three steps at the incident surface end of the first echelon grating region, and then forming a hollow circular hole at the bottom, wherein the The height of the hollow circular hole is equal to 3d _⊥ .

6 . The microlens according to claim 5 , wherein the focal position of the first echelle grating region is coplanar with the incident surface, and the focal point of the second echelle grating region is coplanar. 7 . The position is coplanar with the bottom end of the first echelle region.

7 . The microlens according to claim 1 , wherein the selection range of n is 1.0 to 3.0, and the equivalent negative refractive index of the echelle grating is n _eff . 8 . The selected range is -1.0 to -0.8, and the range of the operating wavelength λ ₀ is 0.4 μm to 2.0 μm.

8 . The microlens according to claim 1 or 2 , wherein the value range of the f ₁ is 4 μm-6 μm, and the value range of the f ₂ is 6 μm-9 μm. 9 . , f ₂ -f ₁ is controlled at 1μm-2μm.