CN111198447A - Optical cage based on phase gradient super-structured grating and application thereof - Google Patents
Optical cage based on phase gradient super-structured grating and application thereof Download PDFInfo
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- CN111198447A CN111198447A CN201911066113.0A CN201911066113A CN111198447A CN 111198447 A CN111198447 A CN 111198447A CN 201911066113 A CN201911066113 A CN 201911066113A CN 111198447 A CN111198447 A CN 111198447A
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Abstract
The invention discloses an optical cage based on a phase gradient super-structure grating and application thereof, wherein the optical cage comprises a plurality of periodic structures which are in a circular ring shape and are periodically distributed, each periodic structure comprises a plurality of structural units, each structural unit comprises metal and a medium material, the metal and the medium material in each periodic structure are distributed at intervals, and the medium material is a material for generating a gradient abrupt phase. According to the optical cage designed by combining the abrupt phase concept covering 2 pi with the traditional metal sub-wavelength grating, when the number of the structural units in a periodic structure is positive and even, the mutual interference between the electromagnetic waves radiated by each structural unit is cancelled, so that the electromagnetic energy leaked to the outside of the cage is geometrically zero, and the capability of trapping photons by the super-structured cage has strong robustness.
Description
Technical Field
The invention relates to the technical field of optics, in particular to an optical cage based on a phase gradient super-structured grating and application thereof.
Background
In the past few years, scientists have proposed the concept of a graded metamaterial surface by introducing an abrupt phase covering a 2 pi change along the interface direction in one period, and further introducing an effective wave vector ξ in the direction, according to the conservation of momentum in the tangential direction, light reflecting and refracting at the interface satisfies the broad laws of reflection and refraction, k0sinθi＝k0sinθr/t+ ξ, so that the reflection, refraction and wave front of the light can be effectively controlled.
The concept of local abrupt phase provides a new dimension for controlling light propagation, and based on the concept and the law of generalized reflection and refraction, scientists propose a series of ultrathin devices to realize asymmetric transmission, a planar metamaterial lens, a photon spin hall effect and the like. Since the conversion efficiency is limited due to impedance mismatch problems with graded superstructure surfaces, it has been considered in recent years to manipulate light propagation with a non-ultra-thin graded superstructure surface.
Like ultra-thin metamaterial surfaces, such graded metamaterial surfaces are periodic in structure, being thicker, like conventional gratings; however, unlike conventional gratings, the interface of the graded metamaterial surface has a covering abrupt phase, which can modulate each diffraction order, and the thicker graded metamaterial surface is referred to as a "metamaterial" for short. The study showed that: the gradient super-structure grating not only has various abnormal optical characteristics in the super-structure surface, but also has higher conversion efficiency.
Therefore, in view of the above technical problems, there is a need to provide an optical cage based on a phase-graded superlattice grating and an application thereof.
Disclosure of Invention
In view of this, the present invention provides an optical cage based on a phase-gradient super-structured grating and an application thereof, so as to realize trapping of spot source energy in the optical cage.
In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:
an optical cage based on a phase gradient super-structure grating comprises a plurality of periodic structures which are circular rings and are periodically distributed, each periodic structure comprises a plurality of structural units, each structural unit comprises metal and medium materials, the metal and the medium materials in each periodic structure are distributed at intervals, and the medium materials are materials for generating gradient abrupt phase.
As a further improvement of the invention, the inside and outside of the optical cage is air and the refractive index is 1.
As a further improvement of the invention, the refractive index of the dielectric material is n i1+ (i-1) λ/md, λ being the wavelength of the point source within the optical cage, m being the number of structural units of one period, d being the thickness of the structural units.
As a further improvement of the present invention, the waves generated by the point sources within the optical cage are TM waves.
As a further improvement of the invention, m is a positive even number.
As a further improvement of the invention, the ratio delta of the offset distance delta R of the point source from the center of the optical cage to the inner diameter R of the optical cage satisfies delta < 0.3.
As a further refinement of the invention, the point source is located in the center of the optical cage, i.e. Δ ═ 0.
As a further improvement of the present invention, the metal in the structural unit is silver.
The technical scheme provided by one embodiment of the invention is as follows:
an application of an optical cage based on a phase gradient super-structure grating is disclosed, wherein the optical cage is applied to a radome and a photon isolation device.
The invention has the beneficial effects that:
according to the optical cage designed by combining the abrupt phase concept covering 2 pi with the traditional metal sub-wavelength grating, when the number of the structural units in a periodic structure is positive and even, the mutual interference between the electromagnetic waves radiated by each structural unit is cancelled, so that the electromagnetic energy leaked to the outside of the cage is geometrically zero, and the capability of trapping photons by the super-structured cage has strong robustness.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic diagram of the structure of an optical cage where m is 6 according to the present invention;
FIG. 2 is a schematic diagram of the optical cage structure when m is 7;
3a, 3b are the transmission spectrum and magnetic field mode space distribution diagram of the photon cage when m is 6 respectively;
FIGS. 4a and 4b are the transmission spectrum and the magnetic field mode space distribution diagram of the photon cage when m is 7;
FIG. 5 is a graph showing the transmittance ratio for different values of m obtained by simulation and analytical calculation in accordance with the present invention;
FIG. 6a is a schematic diagram of an optical cage with a point source off center according to the present invention in a non-ideal state;
fig. 6b and 6c show transmission patterns in which the point source is gradually off-center when m is 6 and m is 7, respectively.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention, and it is obvious that the described embodiment is only a part of the embodiment of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention discloses an optical Cage with a sub-wavelength metal structure, which is called a super-structure Cage (Meta-Cage) for short. The super-structure cage is a periodic structure, and m different structural units are contained in one periodic structure. Numerical simulations and rigorous analytical calculations show that: the ability of the super-cage to trap light is related to the parity of the number m of building blocks. Specifically, when the number m of the units is odd, the point source placed in the cage can radiate 100% outside the cage without obstruction; when the number of units m is even, the point sources placed in the cage can hardly radiate outside the cage, and all the energy is localized in the cage.
Referring to fig. 1 and 2, an optical cage 100 in the present invention includes a plurality of periodic structures 10 in a circular ring and periodically distributed, each periodic structure 10 includes a plurality of structural units, each structural unit includes a metal 11 and a dielectric material 12, the metal 11 and the dielectric material 12 in each periodic structure 10 are distributed at intervals, the dielectric material is a material that generates a gradual change and abrupt phase, m is the number of structural units in one periodic structure, and m is 6 and m is 7 in fig. 1 and 2, respectively.
As shown in FIG. 1, each period in the optical cage is composed of 6 structural units, the metal 11 in each periodic structure 10 is metallic silver, the dielectric material 12 is a material capable of generating a gradual change abrupt phase, each structural unit has a width of w and a thickness of d, and the units are filled with different refractive indexes of niThe refractive index of the dielectric material 12 is n i1+ (i-1) λ/md, λ is the wavelength of the point source inside the optical cage, i 1, 2.. 6, the inside and outside of the optical cage are both air, and the refractive index is 1.
The following relation is satisfied by the tangential momentum conservation incident angle and refraction angle:
k0sinθi＝k0sinθt- ξ + nG, where θiAnd thetatRespectively representing the angle of incidence and the angle of refraction,
is used to represent the gradient of the abrupt phase generated by the graded grating, G ═ 2 pi/p is generated by the reciprocal lattice vector, and n is the diffraction order. In the super-structured grating, only the cases where n is 0 and n is ± 1 are considered for simplicity.
A point source is placed at the very center of the optical cage where only the transverse magnetic field mode, i.e., TM waves, is considered. Referring to fig. 3a, which shows a transmission map of the photon cage when m is 6, a magnetic field mode of each point is calculated by using COMSOL along a straight line passing through a center of a circle, and an image of the magnetic field mode of each period is drawn, as shown in fig. 3b, because of the high symmetry of the structure, only half of the magnetic field mode, namely the magnetic field mode from the center of the circle to 8R, is considered, a shaded part in fig. 3a shows the magnetic field mode of a TM wave inside the grating, and the magnetic field mode outside the grating is on the right side.
It can be seen that after the TM wave passes through such a cage, the magnetic field mode outside the photon cage is 0, i.e. the TM wave is totally reflected back inside the cage, which is consistent with the results of previous studies.
Referring to fig. 2, which is a schematic structural diagram of the optical cage when m is 7, the number of structural units per period is 7, and the refractive index of the dielectric material 12 is n i1+ (i-1) λ/md, λ is the wavelength of a point source in the optical cage, m is the number of structural units in a period, d is the thickness of the structural units, i is 1, 2.
Referring to fig. 4a, which is a graph showing the transmission pattern of the photon cage when m is 7, a magnetic field mode of each point is calculated by using COMSOL along a straight line passing through the center of a circle, and an image of the magnetic field mode of each period is drawn, as shown in fig. 4b, a shaded part in fig. 4a shows the magnetic field mode of the TM wave inside the grating, and the right side shows the magnetic field mode outside the grating.
It can be found that when m is 7, the electromagnetic wave can be almost completely transmitted through such a grating, and when m is 6, the electromagnetic wave can hardly transmit through such a grating.
By simulating the situation at other m values, a new conclusion is reached:
when m is an odd number, the electromagnetic wave can almost completely transmit through the grating, and when m is an even number, the electromagnetic wave can hardly transmit through the grating.
Of course, it is only preliminary to draw such a conclusion, because the computation is not rigorous enough using the COMSOL simulation, and the correctness of the conclusion is more reliable by using a more rigorous manner to prove the invention. The following is a specific analytical calculation process based on maxwell's equations.
First, since the incident is a TM wave, we write the magnetic field strength of the incident surface:
and the magnetic field intensity of the exit surface:
and the magnetic field strength in the metal bath:
in which we give
And
if the incident and transmission plane media are the same, then gamma3，n＝γ1，n. If the grating material is a perfect electrical conductor or if the dielectric constant is a large negative number, g (x) is 1, v is the index of the gap filling medium and n is the refractive index of the gap filling medium.
Then using Maxwell's equations
The corresponding electric field strength can be expressed as:
wherein:
χi＝vi/ε2。
finally, using the relationship of edge value, when y is 0, H1＝H2，E1x＝E2xWhen y is H, H2＝H3，E2x＝E3xA set of polynomial equations is obtained:
wherein:
f＝w/p。
the required transmission and reflection of the 0 th diffraction order, i.e. the
With the above formula, the transmittance and reflectance in a plurality of cases can be calculated.
Fig. 5 is a graph comparing the results of the simulation and the analysis calculation, in which asterisks indicate the transmittance of the simulation and balls indicate the transmittance of the analysis calculation, and it can be found that the two are comparable.
This confirms the optical properties of the odd-even periodic photon cage, in comparison with the previous conclusions of the system: when m is an odd number, the electromagnetic wave can almost completely transmit through the grating, and when m is an even number, the electromagnetic wave can hardly transmit through the grating.
The above discussion has been of the case where the magnetic flow (i.e., the point source) is placed in the center of the optical cage, but in practice, it is difficult to achieve this placement in the exact center. Although parity of the grating transmittance has been obtained, it is based on the ideal situation, and it is also discussed whether or not this property is still true or to what extent in the non-ideal situation, the parity is significantly affected, in other words, it is necessary to check whether the robustness of the optical cage is good enough so that the structure can be stably put into use.
Continuing with the COMSOL simulation, as shown in fig. 6a, the magnetic current (point source) is slowly deviated from the center, and the deviation distance Δ R of the magnetic current from the center is set as Δ, and the ratio of the deviation distance Δ R to the radius R in the ring is set as Δ, then Δ is increased from 0, as shown in fig. 6b and 6c, it is found that when Δ > 0.3, the effect of the photon cage with odd-even period starts to be obviously weakened, in other words, when the deviation ratio Δ > 0.3, the transmittance of the grating with odd period is obviously weakened, and the transmittance of the photon cage with even period is obviously increased.
Originally, the electromagnetic wave is placed at the center (Δ ═ 0), and this is a very special case when the electromagnetic wave corresponds to each point of the normal incidence grating, but once deviated from this point, the normal incidence is no longer obtained for each point, the incidence angle is no longer 0, and the degree of transmission is dependent on the magnitude of the incidence angle, and therefore inevitably changes. The deviation ratio was constantly changed, and it was found that the influence on the degree of transmission was small when the degree of deviation was small, and that the transmittance t was greatly influenced when Δ > 0.3 as a result of simulation once the degree of deviation was small. Therefore, in order to utilize the special optical characteristics of the structure, it is only necessary to keep the optical characteristics within a certain deviation range without reaching the very special condition of the center.
Therefore, in the present invention, the ratio Δ between the offset distance Δ R of the point source from the center of the optical cage and the inner diameter R of the optical cage satisfies Δ ≦ 0.3, and preferably, the point source is located at the center of the optical cage, i.e., Δ ≦ 0.
Because the optical characteristics can be displayed without depending on extreme positions, the photon cage can play an important role in the fields of high-efficiency sensing detection, imaging, communication and the like. The proposed concept of the super-structured grating can also provide a new idea for simplifying the planar optical device, so that the super-structured grating can be applied to more applications in the aspects of integration and miniaturization of the optical device.
The optical cage based on the phase gradient super-structured grating has the characteristic of perfectly trapping photons/optical fields, and can provide a new thought and theoretical basis for designing novel radar antenna covers and photon isolation devices.
According to the technical scheme, the invention has the following beneficial effects:
according to the optical cage designed by combining the abrupt phase concept covering 2 pi with the traditional metal sub-wavelength grating, when the number of the structural units in a periodic structure is positive and even, the mutual interference between the electromagnetic waves radiated by each structural unit is cancelled, so that the electromagnetic energy leaked to the outside of the cage is geometrically zero, and the capability of trapping photons by the super-structured cage has strong robustness.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (9)
1. An optical cage based on a phase-gradient super-structure grating is characterized in that the optical cage comprises a plurality of periodic structures which are circular rings and are periodically distributed, each periodic structure comprises a plurality of structural units, each structural unit comprises metal and a medium material, the metal and the medium material in each periodic structure are distributed at intervals, and the medium material is a material for generating gradient abrupt phase.
2. The optical cage based on the phase-graded metamaterial grating of claim 1, wherein the inside and outside of the optical cage is air and the refractive index is 1.
3. Phase gradient based superstructure according to claim 2An optical cage for a grating, said dielectric material having a refractive index ni1+ (i-1) λ/md, λ being the wavelength of the point source within the optical cage, m being the number of structural units of one period, d being the thickness of the structural units.
4. The phase graded superstructure grating based optical cage of claim 3, wherein the wave generated by a point source inside the optical cage is a TM wave.
5. The phase graded superstructure grating based optical cage of claim 3, wherein m is a positive even number.
6. The phase graded superstructure grating based optical cage of claim 3, wherein a ratio Δ between a deviation distance Δ R of the point source from the center of the optical cage and an inner diameter R of the optical cage satisfies Δ ≦ 0.3.
7. The optical cage of claim 6, wherein the point source is located at the center of the optical cage, i.e. Δ ═ 0.
8. The phase graded superstructure grating based optical cage of claim 1, wherein the metal in the structural units is silver.
9. Use of an optical cage based on a phase-graded metamaterial grating as claimed in any one of claims 1 to 8 in a radome, photonic isolation device.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN111681634A (en) * | 2020-07-01 | 2020-09-18 | 南京航空航天大学 | Acoustic vortex separator based on angular super-structure surface |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107179576A (en) * | 2017-06-05 | 2017-09-19 | 苏州大学 | A kind of gradual change phase metal grating of visible light wave range |
| CN210742622U (en) * | 2019-11-05 | 2020-06-12 | 苏州大学 | Optical cage based on phase gradient super-structure grating |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN107179576A (en) * | 2017-06-05 | 2017-09-19 | 苏州大学 | A kind of gradual change phase metal grating of visible light wave range |
| CN210742622U (en) * | 2019-11-05 | 2020-06-12 | 苏州大学 | Optical cage based on phase gradient super-structure grating |
Non-Patent Citations (2)
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| ERTING QIAN: "Total omnidirectional reflection by sub-wavelength gradient metallic gratings" * |
| 钱二停: "带突变相位光栅的异常散射特性及相关器件设计研究" * |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN111681634A (en) * | 2020-07-01 | 2020-09-18 | 南京航空航天大学 | Acoustic vortex separator based on angular super-structure surface |
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