CN111208594B - Super-grating element structure insensitive to broadband visible light polarization and application thereof - Google Patents

Super-grating element structure insensitive to broadband visible light polarization and application thereof Download PDF

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CN111208594B
CN111208594B CN202010180206.2A CN202010180206A CN111208594B CN 111208594 B CN111208594 B CN 111208594B CN 202010180206 A CN202010180206 A CN 202010180206A CN 111208594 B CN111208594 B CN 111208594B
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silver
visible light
broadband
dispersion
insensitive
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CN111208594A (en
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万成伟
李仲阳
郑国兴
李子乐
代尘杰
邓联贵
杨睿
时阳阳
万帅
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Wuhan University WHU
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1809—Diffraction gratings with pitch less than or comparable to the wavelength
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1814—Diffraction gratings structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings

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Abstract

The invention discloses a broadband visible light polarization insensitive ultra-grating element structure and application thereof. The element structure is an array composed of unit structures, and each silver geometric body, a silicon dioxide layer and a silver reflecting layer corresponding to the silver geometric body form the unit structures; the unit structure has broadband response to visible light; the unit structure is insensitive to polarization; the unit structures are periodically arranged to form an array, so that broadband dispersion can be realized. The invention has small structure scale, easy integration, strong capability of dispersing visible light wave band and large coverage range of dispersion angle, and can be used for optical wave frequency analysis in spectrometers, spectrometers and the like.

Description

Super-grating element structure insensitive to broadband visible light polarization and application thereof
Technical Field
The invention relates to the field of micro-nano optics and optical dispersion, in particular to a broadband visible light polarization insensitive ultra-grating element structure and application thereof.
Background
The conventional optical dispersion phenomenon is caused by the propagation speed (refractive index) of light along with the frequency (wavelength) of the light wave when the light propagates in a medium. The traditional dispersion element comprises a prism and a grating, and the dispersion of the prism depends on accumulated optical path difference, so that the element size is larger; the grating uses diffraction phenomena, and the resulting dispersion will exist in order ± 1 and other orders. For common super-surfaces, such planar structures are typically very sensitive to light polarization, i.e. exhibit different optical responses for different polarizations, due to the properties of the materials and the specific geometry. Second, conventional gratings, which operate on the basis of conventional geometric and diffractive optics, operate on the principle of passing light through a periodically arranged array to cause rapid changes in phase and/or polarization. However, both critical optical fields, plasma and diffractive optics, have been independently studied and developed. Therefore, the research and investigation of the architectural hybridization between the plasma super surface and the general diffraction grating is insufficient. Also, it is unclear in the field of nanophotonics how the interaction between the plasmon effect and the grating effect affects the performance of emerging nanoscale optical devices.
In recent years, elements having a dispersion function based on a metamaterial have been proposed, and the adjustment of the phase of an optical wave is changed from an accumulation process of an optical path difference to a phase gradient change of a two-dimensional surface based on a generalized catadioptric law. The phase change of the two-dimensional surface can be used for realizing the regulation and control of the refraction or reflection angle, so that the dispersion element is reduced to an ultramicro size. There are some problems to be solved. For example, "Li Z, Palacios E, Butun S, et al, visual-frequency measurements for broadband and polarization recovery and high-efficiency polarization [ J ]. Nano drivers, 2015,15(3): 1615-.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a broadband visible light polarization insensitive ultra-grating element structure and application thereof.
In order to achieve the purpose, the scheme provided by the invention is as follows:
in a first aspect, the present invention provides a broadband visible light polarization insensitive supergrating device structure, characterized in that: comprises a dielectric substrate layer; the dielectric substrate layer is composed of a lower silver reflecting layer and an upper silicon dioxide layer;
a plurality of silver geometric bodies with the same size are arranged on the silicon dioxide layer; the silver geometric bodies are arranged on the medium substrate layer in a cycle of 800nm in the X direction and 200nm in the Y direction; the structural sizes of the silver geometric bodies are all sub-wavelength sizes;
each silver geometry and the 800 x 200nm underneath it2The silicon dioxide layer and the silver reflecting layer form a unit structure; the unit structure is insensitive to polarization and responds to broadband visible light wave band(ii) a The unit structures are periodically arranged in the X direction with 800nm and the Y direction with 200nm as a period to form an array, so that broadband dispersion can be realized.
Preferably, the silver geometric body is of a frustum pyramid structure.
Further, an optimally designed unit structure is obtained by taking the dispersion effect of the broadband as an optimization object; the width of the wide side of the silver geometry is W1The height of the wide side is H1The width of the narrow side is W2And the height of the narrow side is H2(ii) a The thickness of the silicon dioxide layer is d;
the optimization parameters are as follows: w1＝100nm、H1＝30nm、W2＝30nm、H2＝100nm，d＝30nm；
The size of the unit structure is 800nm at the long side and 200nm at the short side.
In a second aspect, the present invention provides an application of the above-mentioned ultra-grating device structure insensitive to broadband visible light polarization in realizing high-performance dispersion in the visible light band.
Compared with the traditional element, the invention has the following advantages and beneficial effects:
(1) the dispersion element of the invention has strong dispersion capability and large dispersion angle range, and only has + 1-level dispersion.
(2) The unit structure of the element has ultramicro size, so the element also has the important advantages of small volume, light weight, easy integration and the like, and can be widely applied to the field of spectrometer integration and other photon integration.
Drawings
FIG. 1 is a schematic diagram of the structure of a unit according to the present invention;
FIG. 2 is a schematic diagram of the arrangement of the unit structure array according to the present invention;
FIG. 3 is a simulation graph of the variation of the dispersion angle with the wavelength after the element is vertically irradiated by the linearly polarized light in the x direction in the embodiment of the present invention;
FIG. 4 is a simulation graph showing the variation of the dispersion angle with the wavelength after the element is vertically irradiated by the linearly polarized light in the y direction in the embodiment of the present invention;
FIG. 5 is a simulated plot of dispersion angle as a function of wavelength after orthogonally polarized light perpendicularly illuminates an element in an embodiment of the present invention;
in the figure: w1Is the width H of the wide side of the silver geometric body1Is the height, W, of the silver geometric body broadside2Is the width H of the narrow side of the silver geometric body2Is the height of the narrow side of the silver geometry.
Detailed Description
In order to more clearly explain the structure of the present invention and the functions realized by the same, the present invention is further described in detail by referring to the specific embodiments in the attached drawings.
Example 1
The embodiment is a specific design process of a broadband visible light polarization insensitive ultra-grating element structure.
Optimizing and designing the unit structure by using electromagnetic simulation software FDTD Solutions, taking the dispersion effect of a broadband as an optimization object, and scanning the width W of the wide side of the silver geometric body1Height H of the broadside1Width W of narrow side2And the height H of the narrow side2The thickness d of the silicon dioxide layer, to obtain the optimum parameters for the desired function. Through optimization calculation, the finally obtained optimization parameter is W1＝100nm、H1＝30nm、W2＝30nm、H2The unit structure has the size of a long side of 800nm and a short side of 200nm, wherein d is 100nm and 30 nm. Fig. 1 is a schematic diagram of a cell structure. The unit structures are periodically arranged in the x-direction and the y-direction, as shown in fig. 2, to constitute a silver geometrical array. When a beam of white light is vertically incident on the array surface from right above the array, an abnormal reflection phenomenon occurs, and meanwhile, light with different wavelengths is reflected to different angles, namely, the dispersion of light waves. FIG. 3 simulates the dispersion effect of linearly polarized white light vibrating in the x-direction incident on the array surface using software; similarly, fig. 4 shows the dispersion effect of linearly polarized white light vibrating in the y-direction incident on the surface of the silver geometric array. When white light having an arbitrary polarization state is incident, light corresponding to light having an orthogonal polarization state is incident on the surface of the silver geometry, and the dispersion effect thereof is shown in fig. 5.
In order to facilitate understanding of the technical solution of the present invention, the technical principle that the structure of the present invention can realize the structure of the polarization insensitive ultra-thin visible light broadband dispersion element will be described in detail below:
according to the generalized law of reflection:
Figure GDA0002787907000000041
in the formula [ theta ]iAnd thetarRespectively angle of incidence and angle of reflection, lambda0For the wavelength of the light wave, phi (x) is the phase gradient of the surface along the x-direction, niIs the refractive index of the incident medium. According to the formula, when
Figure GDA0002787907000000051
Is a constant, then the reflection angle thetarThe dispersion phenomenon is caused by the wavelength of the incident light wave, i.e. light waves of different wavelengths have different reflection angles. The design of such a phase gradient is usually in a single direction, i.e. a phase gradient
Figure GDA0002787907000000052
Or
Figure GDA0002787907000000053
The invention designs the constant type phase gradient in the x direction as a constant, and the phase gradient in the x direction can cause the linear polarized light vibrating in the y direction to generate an abnormal reflection phenomenon, namely a dispersion effect.
Since linearly polarized light oscillating in the x direction is insensitive to this phase gradient, the idea of blazed grating is used in the present invention. The blazed grating utilizes the non-parallel of the groove surface and the grating surface to separate the central maximum of single groove surface diffraction from the interference zero-order principal maximum among the groove surfaces, and transfers and concentrates the light energy to a certain level of spectrum from the interference zero-order principal maximum to realize the blazed of the level of spectrum. By utilizing the principle and the idea of blaze, according to the illustration in fig. 1, the silver geometric body has a certain gradient in the z direction, and the dispersion effect same as that of polarized light vibrating in the y direction can be realized for linearly polarized light vibrating in the x direction by optimizing the height and the size of the gradient. And the problem that the original blazed grating is only used for one specific wavelength is solved, so that the working wavelength of the blazed grating is changed into a broadband wavelength.
Example 2
The embodiment is a specific design process of a broadband visible light super-grating with adjustable light splitting and absorption functions.
And optimally designing a unit structure by using electromagnetic simulation software FDTD Solutions, taking the abnormal deflection effect of the light beam as an optimization object, and scanning the width of the wide side, the height of the wide side, the width of the narrow side, the height of the narrow side and the thickness of the silicon dioxide layer of the silver geometric body to obtain the optimal parameters under the expected function. The unit structures are periodically arranged along the x direction and the y direction to form a silver geometrical body array. When a beam of white light vertically enters the array surface from right above the array, the phenomenon that different polarized lights go to different directions occurs, and meanwhile, the lights with different wavelengths are reflected to different angles, so that the light splitting function is realized. When the angle of the incident light is changed, the reflection efficiency is different for the incident light with different angles, and the absorption adjustable function is realized.
The embodiment designs the change of a constant phase gradient in the x direction, and the phase gradient can enable linearly polarized light vibrating along the y direction to generate an abnormal reflection phenomenon; since linearly polarized light vibrating in the x direction is insensitive to this phase gradient, the principle of blazed grating is employed in this example such that linearly polarized light vibrating in the x direction produces a reflection phenomenon opposite to the y direction polarization. The groove surface of the blazed grating is not parallel to the grating surface, so that light energy is gathered to a certain level of spectrum from the interference zero order main maximum, and the blazed spectrum is realized. By utilizing the principle and thought, the silver geometric body of the embodiment has a certain gradient in the z direction, and the dispersion effect same as that of polarized light vibrating in the y direction on linearly polarized light vibrating in the x direction can be realized by optimizing the gradient.
In summary, the invention combines two different principles and methods to design an ultrathin visible light broadband dispersion element structure insensitive to polarization, which has the same dispersion effect on linearly polarized light in the x direction and the y direction. Therefore, the device can be used as a dispersion device for light waves in any polarization state.

Claims (3)

1. A broadband visible light polarization insensitive supergrating element structure, comprising: comprises a dielectric substrate layer; the medium substrate layer is composed of a lower silver reflecting layer (3) and an upper silicon dioxide layer (2);
a plurality of silver geometric bodies (1) with the same size are arranged on the silicon dioxide layer; the silver geometric bodies (1) are arranged on the medium substrate layer in a cycle of 800nm in the X direction and 200nm in the Y direction; the structural sizes of the silver geometric bodies (1) are all sub-wavelength sizes;
each silver geometry (1) and the 800 x 200nm underneath it2The silicon dioxide layer (2) and the silver reflecting layer (3) form a unit structure; the unit structure responds to a broadband visible light wave band and is insensitive to polarization; the unit structures are periodically arranged in the X direction with 800nm and the Y direction with 200nm as a period to form an array, so that broadband dispersion can be realized;
the silver geometric body (1) is of a frustum structure with a slope in the Z direction and wide at the top and narrow at the bottom.
2. A broadband visible light polarization insensitive supergrating element structure according to claim 1, wherein: obtaining an optimally designed unit structure by taking the dispersion effect of the broadband as an optimization object; the width of the wide side of the silver geometric body (1) is W1The height of the wide side is H1The width of the narrow side is W2And the height of the narrow side is H2(ii) a The thickness of the silicon dioxide layer (2) is d;
the optimization parameters are as follows: w1＝100nm、H1＝30nm、W2＝30nm、H2＝100nm，d＝30nm；
The size of the unit structure is 800nm at the long side and 200nm at the short side.
3. Use of a broadband visible light polarization insensitive supergrating element structure as claimed in claim 1 or 2 for achieving high performance dispersion in the visible wavelength band.
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