CN111596390A - Plane grating with light splitting and focusing capabilities - Google Patents
Plane grating with light splitting and focusing capabilities Download PDFInfo
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- CN111596390A CN111596390A CN202010594356.8A CN202010594356A CN111596390A CN 111596390 A CN111596390 A CN 111596390A CN 202010594356 A CN202010594356 A CN 202010594356A CN 111596390 A CN111596390 A CN 111596390A
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Abstract
The invention discloses a plane grating with light splitting and focusing capabilities, which is provided with a parallel light vertical incidence structure, wherein light with different wavelengths can be focused at different positions, the plane grating comprises a plurality of substructures, each substructure comprises a microstructure and a substrate for supporting the microstructure, the substrates of all the substructures jointly form a substrate of an integral structure, and all the substructures jointly form an integral grating structure; the phase corresponding to the center of each substructure in the grating array can be determined by the design wavelength, the design focal length, the focus offset angle and the position corresponding to the center of the substructure, the phase corresponding to the center of each substructure determines the size parameter of the substructure, and the grating can lead the incident light with different wavelengths to be converged on different focuses after passing through the grating, thereby realizing the functions of light splitting and focusing.
Description
Technical Field
The invention relates to a plane grating with light splitting and focusing capabilities, which is used as a light splitting device, can be used for a monochromator and a spectrometer and belongs to the field of geometric optics and micro-nano optics.
Background
The traditional grating is a piece of plane glass or metal sheet engraved with a large number of parallel equal-width equidistant slits (scribed lines), only has the function of dispersion and light splitting, and a focusing lens needs to be additionally added when the grating is used in a spectrometer, so that the simplification of a light path is not facilitated. The concave grating is a reflection grating formed by etching a series of parallel lines on a high-reflection metal concave surface, has light splitting and focusing capabilities, but has the defects of serious astigmatism problem, low diffraction efficiency and difficult mechanical etching, so that the concave grating is not widely applied.
The super-surface is an ultrathin two-dimensional surface consisting of a series of sub-wavelength structures, and can realize effective regulation and control on the aspects of amplitude, phase, polarization state and the like of incident beams. The diffraction grating enables the phase of incident light to be subjected to periodic spatial modulation through a regular structure, and after polychromatic light passes through the grating, spectral lines with different wavelengths appear at different positions to form a spectrum, so that the grating can be regarded as a super-surface element. Due to the characteristics of small super-surface volume and high integration level, optical elements designed by using the super-surface optical element are attracted by wide attention.
Disclosure of Invention
1. Objects of the invention
The invention aims to provide a plane grating with light splitting and focusing capabilities simultaneously so as to simplify a light path.
2. The technical scheme adopted by the invention
The invention discloses a plane grating with light splitting and focusing capabilities, which is provided with a parallel light vertical incidence structure, wherein light with different wavelengths can be focused at different positions; the grating structure comprises a plurality of substructures, each substructure comprises a microstructure and a substrate for supporting the microstructure, the width of the substructure is T, the microstructure is a cuboid, the width of the microstructure is L, the height of the microstructure is H, the substrates of all the substructures form the substrate of the integral structure together, and all the substructures form the integral grating structure together;
by adjusting the size parameters (such as duty ratio and width T) of each substructure, the phase of emergent light can be changed differently;
determining the phase distribution of the grating surface according to the focusing requirement by the following formula, thereby determining the size parameter of each substructure;
wherein, the surface of the grating is used as the origin with the center as phi(x)Is the phase at the coordinate point (x), λ is the designed incident light wavelength, f is the distance from the focal point to the center of the grating, α is the angle of the focal point from the axis, m is any integer, by setting the phase φ at each of the different positions on the grating surface(x)Determining parameters of each cuboid microstructure unit; the phase distribution of the whole grating is adjusted by changing the size parameter of each substructure, so that the focusing function of the grating is realized.
Further, the width T of the substructure ranges from 300nm to 1000nm, and different phases can be obtained by adjusting the width or duty cycle of the substructure.
In order to improve the phase modulation capability and the transmissivity of the microstructure, the cuboid component material of the microstructure is silicon or titanium dioxide.
Furthermore, the width L of the cuboid of the microstructure is 30nm to 800nm, the height H is 1000-5000nm, the duty ratio of the substructure is defined as L/T, and different phases can be obtained by adjusting the duty ratio of the substructure.
Further, the spectral ranges for the grating are the infrared band and the visible band.
In order to improve the transmittance of the grating, the substrate component material is silicon dioxide.
Further, a phase coverage of 2 pi is achieved when the microstructure height H is 1500nm and the duty cycle of the substructure varies between 0.1 and 0.7.
Further, setting the boundary condition of the microstructure in the X direction as a periodic boundary condition and setting the boundary condition in the propagation direction of the incident light, i.e., the Y direction as a PML boundary condition, the relationship between the transmittance and the phase change of the incident light and the size (e.g., duty ratio and width) of the substructure is obtained.
Further, the grating has no polarization sensitivity, i.e. the focal point is located the same for incident light of any polarization direction.
3. Advantageous effects adopted by the present invention
(1) The grating provided by the invention consists of a substrate and a cuboid microstructure arranged on the substrate, and the phase modulation of 0 to 2 pi can be realized on incident light by adjusting the size parameters of the substructure.
(2) By setting reasonable wavelength, focal length and angle parameters, the invention can realize the plane grating with light splitting and focusing capabilities.
(3) Meanwhile, the plane grating with light splitting and focusing capabilities has potential application in miniaturization and integration designs of spectrometers, monochromators and other instruments, and has very important research significance.
Drawings
FIG. 1 is a schematic diagram illustrating an overall grating structure according to an exemplary embodiment of the present invention;
FIG. 2 is a front view of an overall grating and a front view of a single substructure structure according to an exemplary embodiment of the present invention;
FIG. 3 is a front view of the overall structure of a grating according to an exemplary embodiment of the present invention;
FIG. 4 is a schematic diagram showing the splitting and focusing of incident light at different wavelengths after passing through a grating;
FIG. 5 is a schematic diagram showing the relationship between the transmittance and the phase change of the outgoing light, and the duty ratio (L/T) and the height (H), respectively, when the wavelength of the incident light is 1500 nm;
FIG. 6 is a schematic diagram of the phase response of the complete grating distribution to linearly polarized light of TE (left) and TM (right) polarization;
FIG. 7 is a field intensity distribution graph of TE polarized linearly polarized light with different wavelengths after incidence along the Y axis, and the dotted line is the determined focal plane position;
FIG. 8 is a graph showing the distribution of the field intensity of TM-polarized linearly polarized light of different wavelengths after incidence along the Y-axis, the dotted line being the determined focal plane position;
FIG. 9 is a graph of the field intensity distribution of light of different wavelengths in the focal plane, with the abscissa indicating the position in the focal plane, the ordinate indicating the magnitude of the field intensity, and each line indicating a different wavelength;
FIG. 10 is a graph of the field intensity distribution of light of different wavelengths in the focal plane, with the abscissa indicating the wavelength, the ordinate indicating the position in the focal plane, and the color scale indicating the magnitude of the field intensity;
FIG. 11 shows the relationship between the transmittance and phase variation of the outgoing light and the substructure width T at an incident light wavelength of 532 nm;
fig. 12 is a field intensity distribution diagram of TE polarized linearly polarized light of different wavelengths after incidence along the Y axis, and the dotted line is a determined focal plane position.
Detailed Description
The technical solutions in the examples of the present invention are clearly and completely described below with reference to the drawings in the examples of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without inventive step, are within the scope of the present invention.
The present invention will be described in further detail with reference to the accompanying drawings.
Example 1
Referring to fig. 1, a planar grating with both light splitting and focusing capabilities includes a plurality of sub-structures, each sub-structure includes a microstructure 1 and a portion of a substrate supporting the microstructure, a portion of the substrate of each sub-structure forms a substrate 2 of the grating, and the microstructures of all the sub-structures form a grating array. The grating can lead the incident light with different wavelengths to be converged at different focuses after passing through the grating, thereby realizing the functions of light splitting and focusing. In the invention, each cuboid microstructure unit in the grating is equivalent to a phase shifter, and after incident light passes through the phase shifter, an additional phase difference is added, the size of the additional phase difference is related to the parameters of the structure, and through reasonable design parameters, the phase shift of 0 to 2 pi can be realized and higher transmissivity can be obtained.
As shown in fig. 2, any microstructure and the portion of the substrate supporting it can be referred to as a sub-structure of the grating, with each sub-structure arranged to form the grating. The length of the substructure in the X direction is T, the height of the microstructure is H, the width is L, and the duty cycle of the substructure is defined as L/T.
The phase distribution of the grating surface can be determined by the following formula according to the actual focusing requirement, and then the size parameter of each substructure is determined according to the data of simulation (the relationship between the size parameter and the phase of the substructure, fig. 5).
Wherein, the surface of the grating is used as the origin with the center as phi(x)Is the phase at the coordinate point (x), λ is the designed incident light wavelength, f is the distance from the focal point to the center of the grating, α is the angle of the focal point from the axis, m is any integer, as shown in FIG. 3(x)The size parameter for each substructure unit is determined (L, T, H).
To improve the transmittance of the grating, the substrate material is preferably silicon dioxide. In order to improve the phase modulation capability and transmittance of the microstructure, the microstructure material is preferably silicon or titanium dioxide. In order to ensure the high transmittance of the grating and realize the phase regulation of 0-2 pi, the sub-structure of the grating can be subjected to analog simulation and numerical analysis by using a time domain finite difference method (FDTD).
The cuboid microstructure material was provided as silicon with a refractive index of 3.48, the substrate as silicon dioxide with a refractive index of 1.45 and a thickness of 1000nm, the length (T) of the substructure was fixed at 300nm, the wavelength of the incident light was 1500nm, the boundary condition of the microstructure in the X direction was provided as a periodic boundary condition, and the boundary condition in the propagation direction of the incident light (Y direction) was provided as a PML boundary condition, where the incident light mentioned here was linearly polarized light of TE polarization (the definition of polarized light is see fig. 4). After simulation, the transmittance of the incident light was obtained as a function of the duty ratio (L/T) and the height (H), respectively, as shown in fig. 5.
Further, the relationship between the phase change of the incident light (the phase when the duty ratio (L/T) is 0.1, and the unit is rad) and the duty ratio (L/T) and the height (H) is obtained.
As can be seen from fig. 5, when the microstructure height H is 1500nm and the duty cycle of the substructure varies between 0.1 and 0.7, a phase coverage of 2 pi can be better achieved and its transmittance for incident light is generally higher.
Based on the above simulation results and numerical analysis, a complete grating can be designed, the focal length f of the grating can be set to 30 mm, the angle can be set to 15 degrees, and the design wavelength can be set to 1500 nm. Fig. 6 shows the phase response of the complete grating distribution to linearly polarized TE (left) and TM (right) polarizations, which can be found to be slightly different, so that the grating also has focusing and splitting effects on linearly polarized TM polarizations.
The effect of incident light after passing through the grating can be obtained through simulation, fig. 7 is a field intensity distribution diagram of TE polarized linearly polarized light with different wavelengths after being incident along the Y axis, and a dotted line is a determined focal plane position. Fig. 8 is a field intensity distribution diagram of TM polarized linearly polarized light of different wavelengths after incidence along the Y axis, and the dashed line is the determined focal plane position.
As can be seen from fig. 7 and 8, after passing through the grating, the light with different wavelengths is respectively focused at different positions, thereby realizing the functions of light splitting and focusing.
Fig. 9 and 10 show the field intensity distribution of the incident light with different wavelengths along the focal line direction, and each line in fig. 9 represents the incident light with different wavelengths, so that the obvious light splitting effect can be seen.
Example 2
The design scheme of the planar grating with light splitting and focusing capabilities of the embodiment is different from that of the embodiment 1 in that the material of the microstructure is titanium dioxide, the applicable spectral range of the grating is the visible light waveband, and the phase change generated by the sub-structure is generated by adjusting the width (T) of the sub-structure.
In this example, the rectangular parallelepiped microstructure material is provided as titanium dioxide with a refractive index of 2.5, the substrate is provided as silicon dioxide with a refractive index of 1.45 and a thickness of 1000nm, the width L of the substructure is fixedly set to 50nm, the height H is 3000nm, the wavelength of the incident light is 532nm, the boundary condition of the microstructure in the X direction is set as a periodic boundary condition, and the boundary condition in the propagation direction (Y direction) of the incident light, which is referred to herein as TE-polarized linearly polarized light (the definition of polarized light is shown in fig. 4), is set as a PML boundary condition. After simulation, the relationship between the transmittance of the emitted light, the phase change (the phase when the lateral dimension (T) of the structure is 300nm is defined as 0, and the unit is rad) and the substructure width (T) was obtained as shown in fig. 11.
Based on the above simulation results and numerical analysis, a complete grating can be designed, the focal length f of the grating can be set to 30 mm, the angle can be set to 5 degrees, and the design wavelength can be set to 532 nm.
The effect of incident light after passing through the grating can be obtained through simulation, fig. 12 is a field intensity distribution diagram of TE polarized linearly polarized light with different wavelengths after being incident along the Y axis, and the dotted line is a determined focal plane position, so that it can be seen that the designed wavelength also has a good effect in the visible light band, and the splitting and focusing of the incident light are realized.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A planar grating having beam splitting and focusing capabilities, comprising: a parallel light vertical incidence structure is arranged, and light with different wavelengths is focused at different positions; the grating structure comprises a plurality of substructures, wherein each substructure comprises a microstructure and a substrate for supporting the microstructure, the width of the substructure is T, the microstructure is a cuboid, the width of the microstructure is L, the height of the microstructure is H, the substrates of all the substructures form the substrate of the integral structure together, and all the substructures form the integral grating structure together;
determining the phase distribution of the grating surface according to the focusing requirement by the following formula, thereby determining the size parameter of each substructure;
wherein, the surface of the grating is used as the origin with the center as phi(x)Is the phase at the coordinate point (x), λ is the designed incident light wavelength, f is the distance from the focal point to the center of the grating, α is the angle of the focal point from the axis, m is any integer, and the phase phi of each different position on the grating surface is obtained by reasonable setting parameters(x)Thereby determining each of the sub-structural unit dimension parameters.
2. The planar grating structure of claim 1, wherein the sub-structure width T ranges from 300nm to 1000nm, and different phases can be obtained by adjusting the width or duty cycle of the sub-structure.
3. The planar grating structure of claim 1, wherein: the microstructure is silicon or titanium dioxide.
4. The planar grating structure of claim 1, wherein: the width L of the cuboid of the microstructure is 30nm to 800nm, and the height H is 1000-5000 nm.
5. The planar grating structure of claim 1, wherein: the applicable spectral range is visible light wave band and infrared wave band.
6. The planar grating structure of claim 1 wherein the substrate component material is silicon dioxide.
7. The planar grating structure of claim 1, wherein: the microstructure height H is 1500nm and the duty cycle of the substructure varies between 0.1 and 0.7, achieving a phase coverage of 2 pi.
8. The planar grating structure of claim 1, wherein the boundary condition of the microstructure in the X direction is set as a periodic boundary condition, and the boundary condition in the propagation direction of the incident light, i.e., the Y direction, is set as a PML boundary condition, whereby the relationship between the transmittance of the outgoing light, the phase change, and the size of the substructure, respectively, is obtained.
9. The planar grating structure of claim 1, wherein: the position of the focal point is the same for incident light of any polarization direction.
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Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20130027776A1 (en) * | 2010-04-13 | 2013-01-31 | Wei Wu | Controlling phase response in a sub-wavelength grating lens |
| CN105589130A (en) * | 2014-11-13 | 2016-05-18 | 北京邮电大学 | Power divider, wave divider, polarization beam splitter, and design method thereof |
| CN207263300U (en) * | 2017-10-24 | 2018-04-20 | 中国计量大学 | A kind of spectrometer based on super surface texture |
| CN108445555A (en) * | 2018-05-09 | 2018-08-24 | 华南师范大学 | Super surface lens |
| CN108761585A (en) * | 2018-05-17 | 2018-11-06 | 桂林电子科技大学 | A method of surface structure multi-focus lens is surpassed based on medium |
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2020
- 2020-06-28 CN CN202010594356.8A patent/CN111596390A/en active Pending
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20130027776A1 (en) * | 2010-04-13 | 2013-01-31 | Wei Wu | Controlling phase response in a sub-wavelength grating lens |
| CN105589130A (en) * | 2014-11-13 | 2016-05-18 | 北京邮电大学 | Power divider, wave divider, polarization beam splitter, and design method thereof |
| CN207263300U (en) * | 2017-10-24 | 2018-04-20 | 中国计量大学 | A kind of spectrometer based on super surface texture |
| CN108445555A (en) * | 2018-05-09 | 2018-08-24 | 华南师范大学 | Super surface lens |
| CN108761585A (en) * | 2018-05-17 | 2018-11-06 | 桂林电子科技大学 | A method of surface structure multi-focus lens is surpassed based on medium |
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