CN112946792B - Micro lens for realizing bifocal focusing - Google Patents
Micro lens for realizing bifocal focusing Download PDFInfo
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- CN112946792B CN112946792B CN202110171418.9A CN202110171418A CN112946792B CN 112946792 B CN112946792 B CN 112946792B CN 202110171418 A CN202110171418 A CN 202110171418A CN 112946792 B CN112946792 B CN 112946792B
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- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B3/00—Simple or compound lenses
- G02B3/10—Bifocal lenses; Multifocal lenses
Abstract
The invention discloses a micro lens for realizing bifocal convergence, which is characterized in that: the lens 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 body with a focal length f corresponding to the focal length f 1 And a first step grating zone corresponding to a focal length f 2 Wherein f is a second echelle grating region of 1 ＜f 2 (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. The plano-concave lens designed by the invention can realize bifocal focusing at the same time, and effectively reduce the dispersion degree of focal spots, so that the focusing is more uniform.
Description
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.
The research shows that in the structure with the bifocal lens, a longer flat step exists at the structural boundary corresponding to the focal length, and the 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 f 1 And a first step grating zone corresponding to a focal length f 2 Of (a) a second echelle grating region of (b), wherein f 1 ＜f 2 (ii) a The focus corresponding to the first stepped grating area is lower than the focus corresponding to the second stepped grating area, and the interface of the first stepped grating area and the second stepped grating area intersects at one point in the axial direction; and removing 3 steps at the incident surface end of the first step grating area so as to form a hollow round hole at the bottom.
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 i As a horizontal coordinate variable, z i Is a longitudinal coordinate variable, i is a step serial number,
wherein: realization of f 1 The 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 ⊥ ＝λ 0 /(n-n eff )
in the formula: d ⊥ Is the vertical height of the step, λ 0 For the operating wavelength, n is the refractive index of the dielectric material, n eff Is 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 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 operating wavelength λ 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 f 1 Has a value in the range of 4 to 6 μm, wherein f 2 Has a value range of 6 to 9 μm, f 2 -f 1 The 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 provides 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 the 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 f 1 And a first step grating zone located above and corresponding to a focal length f 2 Wherein f is a second echelle grating region of 1 ＜f 2 . In order to reduce the dispersion degree of the focal spot and enable the focal spot to be more uniform, the second echelon grating region above the second echelon grating region is arranged upwards in designRaising the grating area to enable the focus corresponding to the first stepped grating area to be lower than the focus corresponding to the second stepped grating area, and eliminating a long flat step on the interface of the first grating area and the second grating area to enable the interface of the first stepped grating area and the second stepped grating area to intersect at one point in the axial direction.
In an embodiment of the present invention, the focal length f of the first grating region is preset 1 6 μm, the focal length f of the second grating region 2 And 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 f 1 The upper second grating area is provided with 15 steps to realize the preset focal length f 2 Focusing of (3).
In order to enable the focal spots to be more focused and uniform, the part corresponding to the preset focal length of 8 micrometers 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 micrometers are removed, and finally the plano-concave micro lens which is continuous at the grating structure interface and has the hollow round hole at the bottom for realizing 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 ⊥ ＝λ 0 /(n-n eff )(1)。
(2) Vertical edge vertex coordinates (r) i ,z i )，r i As a horizontal coordinate variable, z i Is a longitudinal coordinate variable, and i is a step serial number.
(a) Lower implementation of the focal length f 1 The focused vertex coordinates of the vertical edges of the steps meet the following relation:
(b) upper part realizing focal length f 2 The focused vertex coordinates of the vertical edges of the steps meet the following relation:
wherein n is eff The negative refractive index is selected to be in the range of-1.0 to-0.8, in this example n eff Calculated as-0.9, operating wavelength λ 0 532nm, 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 (8)
1. A microlens for achieving bifocal gathering, characterized by: comprises using a homogeneous medium materialThe cylindrical lens is made of a material, 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 structure corresponding to a focal length
And a first step grating zone corresponding to a focal length of
Of the second echelle grating region, wherein
(ii) a The focus corresponding to the first stepped grating area is lower than the focus corresponding to the second stepped grating area, and the interface of the first stepped grating area and the second stepped grating area intersects at one point in the axial direction; and removing 3 steps at the incident surface end of the first step grating area so as to form a hollow round hole at the bottom.
2. A microlens for achieving bifocal gathering according to claim 1, wherein: the first step grating region comprises M steps, and the second step region comprises 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
，
In the form of a horizontal coordinate variable,
is a variable of a longitudinal coordinate, and is,
the number of the steps is the serial number of the steps,
wherein: implementation of
The step coordinates of the first step grating region of the focal length satisfy the following relationship:
in the formula
；
；
The step coordinates of the second step grating area satisfy the following relation:
in the formula
；
。
3. A microlens for achieving bifocal gathering according to claim 2, wherein: the vertical height of the steps in the stepped grating structure satisfies the following relationship:
in the formula:
is the vertical height of the steps and,
in order to be at the wavelength of operation,nis the refractive index of the dielectric material,
is an equivalent negative refractive index.
4. A microlens for achieving bifocal gathering according to claim 3, wherein: the inner side wall of the ladder-shaped grating structure is a vertical wall.
5. A microlens for achieving bifocal gathering according to claim 2, wherein: the height of the hollow round hole is equal to
。
6. A microlens for realizing bifocal focusing according to claim 5, wherein: the focal position of the first stepped grating area is coplanar with the incident surface, and the focal position of the second stepped grating area is coplanar with the bottom end of the first stepped grating area.
7. A microlens for achieving bifocal gathering according to claim 3, wherein: the above-mentionednIs selected within a range of1.0 to 3.0, equivalent negative refractive index of the stepped grating
The working wavelength is selected from-1.0 to-0.8
In the range of 0.4 μm to 2.0. mu.m.
8. A microlens for realizing bifocal focusing according to claim 1 or 2, wherein: the above-mentioned
Has a value in the range of 4 μm to 6 μm, said
The value range of (A) is 6-9 μm,
the thickness is controlled to be 1-2 μm.
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Citations (2)
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| CN108535865A (en) * | 2018-05-23 | 2018-09-14 | 南京邮电大学 | A kind of negative refraction grating plano-concave mirror design method that focal length is controllable |
| CN111965746A (en) * | 2020-08-13 | 2020-11-20 | 南京邮电大学 | All-dielectric plano-concave focusing lens with suppressed hollow secondary focus |
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| US5699142A (en) * | 1994-09-01 | 1997-12-16 | Alcon Laboratories, Inc. | Diffractive multifocal ophthalmic lens |
| US20070258143A1 (en) * | 2006-05-08 | 2007-11-08 | Valdemar Portney | Aspheric multifocal diffractive ophthalmic lens |
| SG10201402266XA (en) * | 2009-02-12 | 2014-10-30 | Univ Arizona State | Diffractive trifocal lens |
| JP2013101323A (en) * | 2011-10-21 | 2013-05-23 | Hoya Corp | Multifocal ocular lens |
| IN2015DE01075A (en) * | 2015-04-17 | 2015-06-05 | Prakhyat ROOP | |
| CN106019429B (en) * | 2016-07-13 | 2018-04-10 | 南京邮电大学 | A kind of 1-D photon crystal plano-concave mirror of column vector beam sub-wavelength multiple-point focusing |
| AU2018235011A1 (en) * | 2017-03-17 | 2019-10-24 | Amo Groningen B.V. | Diffractive intraocular lenses for extended range of vision |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108535865A (en) * | 2018-05-23 | 2018-09-14 | 南京邮电大学 | A kind of negative refraction grating plano-concave mirror design method that focal length is controllable |
| CN111965746A (en) * | 2020-08-13 | 2020-11-20 | 南京邮电大学 | All-dielectric plano-concave focusing lens with suppressed hollow secondary focus |
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| A new mechanism for negative;W. T. Lu, Y. J. Huang, P. Vodo, R. K. Banyal, C. H. Perry, and S;《OPTICS EXPRESS》;20070723;第15卷(第15期);全文 * |
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