CN114839772B - Design and implementation method of complex amplitude modulation super-surface device - Google Patents
Design and implementation method of complex amplitude modulation super-surface device Download PDFInfo
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Abstract
The invention discloses a design and implementation method of a complex amplitude modulation super-surface device, and belongs to the field of super-surfaces. The method comprises the following steps: using isotropic cell structures with different geometrical dimensions as basic constituent units of the super-surface device; the unit structure is a cylinder, and the transmittance and the phase of the wavefront can be adjusted simultaneously by changing the radius and the height of the unit structure. The method has the characteristic of insensitivity to polarization, and can realize complex amplitude modulation. In addition, the invention also provides a search algorithm, which has the characteristics of strong robustness and simple implementation, can easily search a uniformly distributed discrete value structure from the two-dimensional parameter scanning data, is not only suitable for the search algorithm, but also suitable for other scenes with similar search requirements.
Description
Technical Field
The invention belongs to the field of super-surfaces, and particularly relates to a design and implementation method of a complex amplitude modulation super-surface device.
Background
The super surface is a two-dimensional form of a metamaterial and consists of a sub-wavelength scale nanostructure array. Such ultra-thin planar devices exhibit an unprecedented ability to manipulate electromagnetic waves by introducing one or more abrupt changes in amplitude, phase, and polarization states. Based on this property, the super-surface has made significant progress in some critical applications.
To date, most metasurfaces have been designed to manipulate only one property of an electromagnetic wave, such as phase, to achieve the goal of manipulating the optical field. While pure phase modulated metasurfaces have shown many surprising capabilities, this does not allow perfect wavefront modulation due to the lack of modulation of the amplitude. More advanced and more complex perfect wavefront modulation technology has great significance for controlling electromagnetic waves, and can directly improve the performance of a plurality of applications based on electromagnetic wave modulation.
With the continuous development of the super-surface, research in recent years has made many attempts and made significant progress in realizing complex amplitude modulation of electromagnetic waves using the super-surface. The methods adopted by the researches are basically based on the principles of geometric phase and polarization conversion, and various anisotropic unit structures are adopted as basic constituent units of the super-surface device to realize the complex amplitude modulation target. For example, based on C-type structures, V-type structures, and X-type structures and their variants, based on a single rectangular structure, based on a plurality of structures constituting a macro-composite structure, based on a multi-layer structure, based on rectangular structures of different heights, and the like.
While these prior efforts have greatly broadened the application of super-surfaces in the field of complex amplitude and even multi-dimensional property modulation, anisotropic cell structures require incident light to have one or more specific polarization states in order for devices composed of such cell structures to function properly. However, in practical application scenarios, there are a large number of polarization independent situations, and there are a considerable number of application scenarios where it is not possible or very difficult to provide a specific polarization state for device operation. The polarization state may be a serious limitation in certain application environments, and many additional devices or apparatuses may be required to pre-process or post-process the incident light to meet the polarization state requirement, which increases the system complexity and reduces the efficiency, and in some cases, it may be difficult to provide light of a specific polarization state.
Disclosure of Invention
Aiming at the defects and improvement requirements of the prior art, the invention provides a design and implementation method of a complex amplitude modulation super-surface device, aiming at solving the technical problems that the prior super-surface device takes various anisotropic unit structures as basic constituent units, and the incident light is required to have one or more specific polarization states, so that the system complexity is high and the efficiency is low.
In order to achieve the above object, in a first aspect, the present invention provides a method for designing and implementing a complex amplitude modulation super surface device, including: using isotropic cell structures with different geometrical dimensions as basic constituent units of the super-surface device; the unit structure is a cylinder, and the transmittance and the phase of the wavefront can be adjusted simultaneously by changing the radius and the height of the unit structure.
Further, each unit structure composing the super surface device is determined by the following steps: s1, orthogonal parameter scanning is carried out on each unit structure through simulation, and the transmittance and the phase modulation amount provided by the unit structures under different geometric parameter combinations are obtained; s2, in the transmittance interval
Taking M discrete values at equal intervals
In a length of
Is equally spaced by N discrete values
So that each transmittance subinterval
There are multiple transmission modulation values, and the phase modulation amount provided by the unit structure corresponding to the multiple transmission modulation values is in all phase subintervals
There are distributions throughout; wherein,
the target maximum transmittance is set as the maximum transmittance,
in order to search for the tolerance error for the transmittance,
error is tolerated for the phase search; s3, according to the sameIn principle, screening a representative transmittance value from a plurality of transmittance modulation values existing in each transmittance subinterval to obtain M representative transmittance values; screening a phase representative value from a plurality of phase modulation values existing in each phase subinterval to obtain N phase representative values; and obtaining M x N corresponding unit structures as basic composition units of the super-surface device.
Further, the S2 specifically is: s21, in the transmittance interval
Taking M discrete values at equal intervals
Screening out the sub-region located in the transmittance
The inner transmittance modulation amount; wherein,
searching for a tolerance error for the transmittance; s22, judging whether the screening result is non-empty for any transmittance subinterval, if so, outputting an M value and executing S23; if not, making M = M-1, and executing S21; s23, in the length of
Is equally spaced by N discrete values
(ii) a S24, judging whether the phase modulation quantity provided by the unit structure corresponding to the screening result in any transmittance subinterval is in all phase subintervals
If yes, making N = N +1, executing S23 until S24 judges no, outputting the N value of the previous iteration and executing S25; if not, let N = N-1, execute S23 until N exists and S24 is judged as yes, and outputIf the value N is not present, the step S24 is judged to be yes, and the step S26 is executed; wherein,
error is tolerated for the phase search; s25, letting M = M +1, executing S21, and if the determination at S22 is yes and there is an N value and the determination at S24 is yes, executing S25; otherwise, the M value output by the previous round of S22 and the N value output by the previous round of S24 are the optimal M value and the optimal N value; s26, setting M = M-1, executing S21, if the determination of S22 is yes and N values exist and the determination of S24 is yes, setting the M value output by S22 and the N value output by S24 as the optimal M value and N value; otherwise, S26 is executed until the optimal M value and N value are obtained.
Further, each unit structure composing the super surface device is determined by the following steps: s1', orthogonal parameter scanning is carried out on each unit structure through simulation, and the transmittance and the phase modulation amount provided by the unit structures under different geometric parameter combinations are obtained; s2' in the transmittance region
Taking N discrete values at equal intervals
In a length of
Is equally spaced by taking M discrete values
So that each phase subinterval
There are multiple phase modulation values, and the transmission modulation amount provided by the unit structure corresponding to the multiple phase modulation values is in all transmission subintervals
There are distributions of them; wherein,
the target maximum transmittance is set as the maximum transmittance,
in order to search for the tolerance error for the transmittance,
error tolerance is searched for the phase; s3', screening a transmittance representative value from a plurality of transmittance modulation values existing in each transmittance subinterval according to the same principle to obtain M transmittance representative values; screening a phase representative value from a plurality of phase modulation values existing in each phase subinterval to obtain N phase representative values; thereby obtaining M × N corresponding unit structures which are used as basic composition units of the super-surface device.
Further, the S2' is specifically: s21' in the length of
Is equally spaced to take N discrete values
Screening out the sub-interval located in the phase
The amount of phase modulation within; wherein,
error is tolerated for the phase search; s22 ', judging whether the screening result of any phase subinterval is non-empty, if so, outputting an N value and executing S23'; if not, making N = N-1, and executing S21'; s23' in the transmittance interval
Taking M discrete values at equal intervals
(ii) a S24', judging the transmission rate modulation quantity provided by the unit structure corresponding to the screening result in all the transmission rate subintervals
If yes, making M = M +1, executing S23 ' until S24 ' judges no, outputting M value of previous iteration and executing S25 '; if not, making M = M-1, executing S23 ' until the M value exists and the S24 ' is judged to be yes, outputting the M value and executing S25 ', and if the M value does not exist and the S24 ' is judged to be yes, executing S26 '; wherein,
searching for a tolerance error for the transmittance; s25 ', make N = N +1, execute S21 ', if S22 ' is determined as yes, and if M exists, make S24 ' be determined as yes, execute S25 '; otherwise, the N value output by the S22 'and the M value output by the S24' in the previous round are the optimal N value and M value; s26 ', making N = N-1, executing S21', if the S22 'is judged yes and the M value exists and the S24' is judged yes, setting the N value output by the S22 'and the M value output by the S24' as the optimal N value and M value; otherwise, S26' is executed until the optimum N and M values are obtained.
Further, the method further comprises: and determining a theoretical complex amplitude distribution of the super-surface device, and selecting the unit structure with the provided complex amplitude modulation quantity closest to the provided complex amplitude modulation quantity from the M-N corresponding unit structures for each theoretical complex amplitude value, thereby forming the super-surface device.
Further, the super-surface device is processed by using a micro-nano three-dimensional manufacturing technology.
Further, the super-surface device is processed by using a laser three-dimensional direct writing technology based on a two-photon polymerization principle.
In a second aspect, the invention provides a complex amplitude modulated super-surface device, obtained by a method as described in the first aspect.
Generally, by the above technical solution conceived by the present invention, the following beneficial effects can be obtained:
(1) Compared with the existing super-surface device which takes various anisotropic unit structures as basic constituent units, the super-surface device requires that incident light has one or more specific polarization states, so that the system is high in complexity and low in efficiency; the invention adopts an isotropic unit structure as a basic unit of the super-surface, has the characteristic of insensitivity to polarization, can realize complex amplitude modulation at the same time, and can realize complex amplitude modulation without depending on any polarization state, which also means that incident light can be in any polarization state or no polarization state.
(2) At present, the super-surface capable of carrying out complex amplitude modulation needs to depend on a specific polarization state, so that in the practical application process of the device, a polarizer, an analyzer and other related devices are needed to carry out pretreatment and post-treatment on the polarization state so as to ensure that the device can normally work, the complexity of the system is increased, and the overall efficiency is reduced to a certain extent. The design characteristics of the invention enable the effect of modulating the complex amplitude of the incident electromagnetic wave to be realized only by a single super surface, compared with the existing research, the system is simpler, the working efficiency is higher, and the simplified system structure means that the robustness of the system is stronger.
(3) The search algorithm provided by the invention has the characteristics of strong robustness and simple implementation, can easily search a uniformly distributed discrete value structure from two-dimensional parameter scanning data, is not only suitable for the invention, but also suitable for other scenes with similar search requirements.
(4) Compared with the traditional CMOS process, the micro-nano three-dimensional processing technology, particularly a laser three-dimensional direct writing system based on a two-photon polymerization principle, has nanometer-scale precision, can freely and freely form a three-dimensional structure without a mask, and is more flexible and efficient in manufacturing process.
Drawings
Fig. 1 is a schematic flow chart of a method for designing and implementing a complex amplitude modulation super-surface device according to an embodiment of the present invention.
Fig. 2 is a schematic view of an isotropic cell structure according to an embodiment of the present invention.
Fig. 3 and fig. 4 are schematic diagrams of amplitude modulation and phase modulation provided by a unit structure under different combinations of geometric parameters obtained by scanning according to an embodiment of the present invention.
Fig. 5 and fig. 6 are schematic diagrams of final distribution of the amplitude and phase search results provided by the embodiment of the present invention, respectively.
FIGS. 7 and 8 are views provided for embodiments of the present invention, respectivelyLG 25 Intensity and phase distribution diagram in mode.
FIGS. 9 and 10 are views provided for embodiments of the present invention, respectivelyLG 05 Intensity and phase distribution diagram in mode.
FIGS. 11 and 12 are views provided for embodiments of the present invention, respectivelyLG 42 Intensity and phase distribution diagram in mode.
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 below with reference to the accompanying drawings and 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. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the present application, the terms "first," "second," and the like (if any) in the description and the drawings are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order.
Referring to fig. 1 and fig. 2 to 12, the present invention provides a method for designing and implementing a complex amplitude modulation super surface device, including:
using isotropic cell structures with different geometrical dimensions as basic constituent units of the super-surface device; the unit structure is a cylinder, and the transmittance and the phase of the wavefront can be adjusted simultaneously by changing the radius and the height of the unit structure.
Fig. 2 is a schematic view of an isotropic cell structure provided in an embodiment of the present invention. The invention uses a cylindrical structure with a circular cross-section, wherein the radius and height of the cylinder serve as adjustable geometrical parameters. The base of the cell structure is chosen to be square.
In fig. 2, R is the radius of the cylinder, H is the height of the cylinder, and W represents the substrate size of the unit structure, and W is also the period length of the unit structure distribution when the super-surface device is subsequently constructed, and W is usually in the sub-wavelength range for the super-surface device. The incident light enters from the lower part of the structure, the amplitude and the phase of the incident light are modulated after passing through the structure, and then the incident light exits, so that the invention provides a transmission type device. It is clear that this form of isotropic cell structure is not sensitive to polarization.
In the traditional super-surface design, a cylindrical structure with the same height is used as a basic unit structure, the equivalent refractive index of the structure is adjusted by adjusting the radius of the cylinder, and then the adjustment quantity of the unit structure to the phase is adjusted, usually, the amplitude modulation quantity is designed, so that the adjustment quantity is as unchanged as possible, in other words, the traditional cylindrical structure can only realize a pure-phase super-surface device.
The design provided by the invention takes the radius and the height of the unit structure as adjustable parameters, so that the adjustment has 2 degrees of freedom, and compared with the traditional unit structure (such as a cylindrical structure with the same height) insensitive to polarization, the design can adjust the complex amplitude of the incident electromagnetic wave by more degrees of freedom.
In the practical application of the super-surface, because the interaction between the electromagnetic wave and the sub-wavelength structure is very complex, the response of a single structure is complex, strong interaction can be formed between a plurality of adjacent structures, and further the forward design is very difficult, a reverse design mode is usually adopted, namely, a large number of parameters are scanned to perform simulation calculation, and appropriate structural parameters are selected from the modulation quantity provided by the parameters. In one case, the complex amplitude structure is selected from a large number of scanning parameters directly to replace the complex amplitude structure without grading. However, for the isotropic cell structure used in the present invention, it is difficult to achieve continuous modulation, so the present invention proposes to select a series of uniformly distributed discrete values as the stepped modulation values in the scan data.
Specifically, each unit structure constituting the super surface device is determined by the following steps:
s1, orthogonal parameter scanning is carried out on each unit structure through simulation, and the transmittance and the phase modulation amount provided by the unit structures under different geometric parameter combinations are obtained.
In this embodiment, the geometric parameters of the unit structure are scanned by orthogonal parameters using a physics-related theory derivation or an electromagnetic calculation algorithm, such as a finite difference time domain algorithm, to obtain the transmittance and the phase modulation amount that can be provided by the unit structures with different heights and radii.
The design proposed by the present invention is further explained below by taking simulation as an example. The simulation sets the wavelength of incident light wave to 633 nm, the unit structure period to 600 nm, the cylindrical unit structure material to be silicon nitride, and the substrate material to be silicon dioxide, it should be noted that the above simulation parameters are only a set of basic parameters selected for explanation and are not limited to the above parameters.
Orthogonal parameter scanning is carried out on the unit structures with the radius ranging from 94 nm to 280 nm and the height ranging from 135 nm to 1000 nm by using an FDTD algorithm to obtain complex amplitude modulation amount provided under each group of geometric parameters, and the transmittance (amplitude) and the phase are respectively extracted to obtain corresponding graphs of the geometric parameters, the amplitude and the phase modulation amount as shown in figures 3 and 4.
Further, in order to remove the influence of singular values due to non-convergence and the like in the actual simulation data on the entire data, the transmittance and the phase scan data are normalized to a standard value range, and the range may be a range of transmittance
，
Is the target maximum transmittanceFor the phase, can be
Or
Or other interval, only the length is required to be
And (4) finishing.
S2, in the transmittance interval
Taking M discrete values at equal intervals
In a length of
Is equally spaced by N discrete values
So that each transmittance subinterval
There are multiple transmission rate modulation values, and the phase modulation amount provided by the unit structure corresponding to the multiple transmission rate modulation values is in all phase subintervals
There are distributions throughout; wherein,
the target maximum transmittance is set as the maximum transmittance,
in order to search for the tolerance error for the transmittance,
errors are tolerated for the phase search.
In this embodiment, after the transmittance and the phase modulation amount provided by the unit structures under different geometric parameter combinations are obtained, the scanning result is searched by using a search algorithm to find a series of unit structures with different geometric dimensions, which can provide different complex amplitude modulation amounts, and specifically, the unit structures need to provide M unit structures distributed as uniformly as possible
Transmittance modulation values in the interval. At the same time, the unit structures can provide N distribution which is as uniform as possible for each transmittance modulation value
Interval (a)
Or
Or other length of
Interval) of the phase modulation values.
In particular, the invention proposes a data search algorithm for finding, in a given series of data, a distribution as uniform as possible between a minimum value of the data and a maximum value of the dataKA discrete value.
The basic idea of the search algorithm is that a smaller number of target searches is assumed firstKTolerance error with larger search
Target interval to be searchedIIs composed of
， 
And
the minimum value and the maximum value of the data distributed in the interval, the number of discrete values in the interval is generally far larger than that of the dataK。
Hypothetical intervalIIs an ideal continuous interval, is easy to calculate and determine,Keach uniformly distributed discrete value is
Considering that the actually processed data is a limited number of intervals which do not necessarily satisfy ideal uniform distribution, tolerance error is combined on the basis of the ideal values, and each discrete value is subjected to
Can obtain a numerical range of
I.e. as long as the actual value does not deviate more than the ideal discrete value
Then it can be considered that these discrete values can all use discrete values
Or another value in the interval. At this time, the error
Has a value constraint interval of
Error tolerance value
Should be far superior to the above constraintsIntervals, e.g. of value less than the above-mentioned constraint interval
Or
And even smaller to ensure that the data searched for is as less fluctuating as possible.
The above numerical intervals are then used to fit the actual whole intervalIAnd filtering is carried out, and only the data in the interval is reserved. If the filtered interval has no effective value, it means that the current data can not be divided intoKAnd if the value can be searched, screening a value to represent the actual discrete value in the interval.
Based on the above idea, the S2 specifically is:
s21, in the transmittance interval
Taking M discrete values at equal intervals
Screening out the sub-region located in the transmittance
The amount of modulation of transmittance in the film; wherein,
searching for a tolerance error for the transmittance;
s22, judging whether the screening result is non-empty or not for any transmittance subinterval, if so, outputting an M value and executing S23; if not, enabling M = M-1, and executing S21;
s23, in the length of
Is equally spaced by N discrete values
；
It is understood that, in step S23, the phase interval selected should be consistent with the interval normalized in step S1.
S24, judging whether the phase modulation quantity provided by the unit structure corresponding to the screening result in any transmittance subinterval is in all phase subintervals
If yes, making N = N +1, executing S23 until S24 judges no, outputting the N value of the previous iteration, and executing S25; if not, making N = N-1, executing S23 until there is N and S24 is determined to be yes, outputting the N and executing S25, and if there is no N, S24 is determined to be yes, executing S26;
wherein,
error tolerance is searched for the phase;
s25, if M = M +1, executing S21, and if the determination of S22 is yes and there is an N value, so that the determination of S24 is yes, executing S25; otherwise, the M value output by the previous round of S22 and the N value output by the previous round of S24 are the optimal M value and the optimal N value;
s26, setting M = M-1, executing S21, and if the determination of S22 is yes and N is present and the determination of S24 is yes, setting the M value output by S22 and the N value output by S24 as the optimal M value and N value; otherwise, S26 is executed until the optimal M and N values are obtained.
Furthermore, the search may be started from the phase interval first, and in this case, the operation S2 may be replaced by:
s2', in the transmittance interval
Taking N discrete values at equal intervals
In a length of
Is equally spaced by taking M discrete values
So that each phase subinterval
There are multiple phase modulation values, and the transmission modulation amount provided by the unit structure corresponding to the multiple phase modulation values is in all transmission subintervals
There are distributions throughout; wherein,
the target maximum transmittance is set as the maximum transmittance,
in order to search for the tolerance error for the transmittance,
errors are tolerated for the phase search.
S3, according to the same principle, screening one transmittance representative value from a plurality of transmittance modulation values existing in each transmittance subinterval to obtain M transmittance representative values; screening a phase representative value from a plurality of phase modulation values existing in each phase subinterval to obtain N phase representative values; thereby obtaining M × N corresponding unit structures which are used as basic composition units of the super-surface device.
In this embodiment, if there are at least 1 value in each filtered sub-interval, the same data selection strategy is adopted for each sub-interval to ensure that the distribution of the overall discrete values is as uniform as possible. For example, data in which the numerical distribution is relatively close to the median value in the subinterval may be selected as the representative value.
In the present simulation data, the final search result distribution is as shown in fig. 5 and 6, a total of 10 discrete amplitude values are found, and at the same time, for the case of the distributionEach discrete amplitude value may correspond to 10 discrete phase values, the search error
， 
As can be seen from the error, the fluctuation error of the 10 discrete amplitude values is less than 8%, and the fluctuation error of the 10 discrete phase values is less than 1.58%, i.e., these values have better uniformity in the respective intervals, which can also be seen from the gray level variation degree shown in fig. 5 and 6.
Finally, 100 unit structures can be found from the simulation data, and the complex amplitude modulation quantity provided by the structures can cover 0 to 1 interval in amplitude and cover 0 to 1 interval in phase
An interval.
Further, after obtaining M × N corresponding cell structures as basic constituent units of the super surface device, by determining a theoretical complex amplitude distribution of the super surface device, for each theoretical complex amplitude value, a cell structure to which a complex amplitude modulation amount supplied is closest is selected from the M × N corresponding cell structures, thereby forming the super surface device.
In this embodiment, for constructing the entire super-surface device, first, a theoretical complex amplitude distribution on the super-surface is determined according to an application target, then, for each complex amplitude value, a structure with the closest complex amplitude modulation amount provided in the searched unit structures is used as a structure of the current pixel position, and by repeatedly applying the above replacement process, the super-surface device composed of the above unit structures can be finally obtained.
The following 1 application case was constructed using these cell structures to demonstrate the excellent complex amplitude modulation capability of the design of the present invention.
The Laguerre Gaussian beam has very high application value in many fields due to carrying orbital angular momentum. The traditional method for generating the Laguerre Gaussian beam is usually realized by pure phase modulation and combining other optical devices, so that the method is complex in steps and low in efficiency, and the Laguerre Gaussian beam generated by the pure phase modulation is low in purity and often generates other high-order undesirable modes. In the invention, a Laguerre Gaussian beam with any mode combination can be directly generated by utilizing a complex amplitude super surface under the condition of insensitive polarization without any other auxiliary devices.
Under the condition of plane wave incidence, paraxial scalar approximation is applied, the beam waist position is set to be z =0, the beam waist radius is 16 μm, the device radius is 60 μm, the complex amplitude distribution of the Laguerre Gaussian beam under a cylindrical coordinate system is solved, and then the unit structure obtained by searching in the front is used for replacement to form the final super-surface device. In the invention, generation is respectively constructedLG 25 、LG 05 AndLG 42 a super-surface device with a Laguerre Gaussian beam of modes. The near-field distribution condition under plane wave incidence is calculated through a finite difference time domain algorithm, and then the distribution condition after the light beam is transmitted for 1m is calculated through a far-field projection algorithm, as shown in fig. 7 to 12.
Simulation results can show that the Laguerre Gaussian beam of the combination of the modes generated by the device provided by the invention has higher quality, the light field generated by the micron-scale device still keeps consistency with the design in strength and phase after being transmitted for 1m, the propagation characteristics of the Laguerre Gaussian beam are met, and the effectiveness of the design provided by the invention is verified.
Finally, the device provided by the invention exceeds the range of the traditional two-dimensional super surface, and the unit structures with different heights make the traditional CMOS-based super surface processing technology difficult to process the three-dimensional super surface device provided by the invention, so that the micro-nano three-dimensional manufacturing technology can be used for carrying out high-precision and free forming on the three-dimensional device.
Preferably, the three-dimensional super-surface device provided by the invention can be processed by using a laser three-dimensional direct writing technology based on two-photon polymerization, compared with the traditional CMOS (complementary metal oxide semiconductor) process, the two-photon three-dimensional direct writing technology can realize the manufacture of any three-dimensional structure without a mask while maintaining the nanometer processing precision, and has better processing efficiency and flexibility.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (11)
1. A method for designing and realizing a complex amplitude modulation super-surface device is characterized by comprising the following steps:
using isotropic cell structures with different geometrical dimensions as basic constituent units of the super-surface device; the unit structure is a cylinder, and the adjustment of the transmittance and the phase of the wavefront can be realized simultaneously by changing the radius and the height of the unit structure;
the unit structures forming the super-surface device are determined by the following steps:
s1, orthogonal parameter scanning is carried out on each unit structure through simulation, and the transmittance and the phase modulation amount provided by the unit structures under different geometric parameter combinations are obtained;
s2, in the transmittance interval
Taking M discrete values at equal intervals
In a length of
Is equally spaced by N discrete values
So that each transmittance subinterval
There are multiple transmission modulation values, and the phase modulation amount provided by the unit structure corresponding to the multiple transmission modulation values is in all phase subintervals
There are distributions throughout; wherein,
the target maximum transmittance is set as the maximum transmittance,
in order to search for the tolerance error for the transmittance,
error is tolerated for the phase search;
s3, according to the same principle, screening one transmittance representative value from a plurality of transmittance modulation values existing in each transmittance subinterval to obtain M transmittance representative values; screening a phase representative value from a plurality of phase modulation values existing in each phase subinterval to obtain N phase representative values; and obtaining M x N corresponding unit structures as basic composition units of the super-surface device.
2. The method for designing and implementing a complex amplitude modulated super surface device according to claim 1, wherein S2 specifically is:
s21, in the transmittance interval
Taking M discrete values at equal intervals
Screening out the sub-region located in the transmittance
The inner transmittance modulation amount; wherein,
searching for a tolerance error for the transmittance;
s22, judging whether the screening result is non-empty for any transmittance subinterval, if so, outputting an M value and executing S23; if not, making M = M-1, and executing S21;
s23, in the length of
Is equally spaced by N discrete values
；
S24, judging whether the phase modulation quantity provided by the unit structure corresponding to the screening result in any transmittance subinterval is in all phase subintervals
If yes, making N = N +1, executing S23 until S24 judges no, outputting the N value of the previous iteration and executing S25; if not, making N = N-1, executing S23 until N value exists and S24 is judged to be yes, outputting the N value and executing S25, and if N value does not exist and S24 is judged to be yes, executing S26;
wherein,
error is tolerated for the phase search;
s25, letting M = M +1, executing S21, and if the determination at S22 is yes and there is an N value and the determination at S24 is yes, executing S25; otherwise, the M value output by the S22 and the N value output by the S24 in the previous round are the optimal M value and the optimal N value;
s26, setting M = M-1, executing S21, and if the determination of S22 is yes and N is present and the determination of S24 is yes, setting the M value output by S22 and the N value output by S24 as the optimal M value and N value; otherwise, S26 is executed until the optimal M value and N value are obtained.
3. A method of designing and implementing a complex amplitude modulated super surface device according to claim 1 or 2, characterized in that the method further comprises:
and determining a theoretical complex amplitude distribution of the super-surface device, and selecting the unit structure with the provided complex amplitude modulation quantity closest to the unit structure from the M x N corresponding unit structures for each theoretical complex amplitude value, thereby forming the super-surface device.
4. The method for designing and implementing a complex amplitude modulation super-surface device according to claim 1, wherein the super-surface device is processed using micro-nano three-dimensional fabrication technology.
5. The method of claim 4 wherein the super surface device is fabricated using a laser three-dimensional direct writing technique based on two-photon polymerization principle.
6. A method for designing and realizing a complex amplitude modulation super-surface device is characterized by comprising the following steps:
using isotropic cell structures with different geometrical dimensions as basic constituent units of the super-surface device; the unit structure is a cylinder, and the adjustment of the transmittance and the phase of the wavefront can be realized simultaneously by changing the radius and the height of the unit structure;
the unit structures forming the super-surface device are determined by the following steps:
s1', orthogonal parameter scanning is carried out on each unit structure through simulation, and the transmittance and the phase modulation amount provided by the unit structures under different geometric parameter combinations are obtained;
s2' in length of
Is equally spaced by N discrete values
In the transmittance interval
Taking M discrete values at equal intervals
So that each phase subinterval
There are multiple phase modulation values, and the transmission rate modulation amount provided by the unit structure corresponding to the multiple phase modulation values is in all transmission rate subintervals
There are distributions throughout; wherein,
the target maximum transmittance is set as the maximum transmittance,
in order to search for the tolerance error for the transmittance,
error is tolerated for the phase search;
s3', screening a transmittance representative value from a plurality of transmittance modulation values existing in each transmittance subinterval according to the same principle to obtain M transmittance representative values; screening a phase representative value from a plurality of phase modulation values existing in each phase subinterval to obtain N phase representative values; thereby obtaining M × N corresponding unit structures which are used as basic composition units of the super-surface device.
7. The method of claim 6, wherein S2' is specifically:
s21' in the length of
Is equally spaced to take N discrete values
Screening out the sub-interval in phase
The amount of phase modulation within; wherein,
error is tolerated for the phase search;
s22 ', judging whether the screening result of any phase subinterval is non-empty, if so, outputting an N value and executing S23'; if not, making N = N-1, and executing S21';
s23' in the transmittance interval
Taking M discrete values at equal intervals
；
S24', for any phase subinterval, the transmission modulation amount provided by the unit structure corresponding to the screening result is judged in all the transmission subintervals
If yes, making M = M +1, executing S23 ' until S24 ' judges no, outputting M value of previous iteration and executing S25 '; if not, making M = M-1, executing S23 ' until the M value exists and the S24 ' is judged to be yes, outputting the M value and executing S25 ', and if the M value does not exist and the S24 ' is judged to be yes, executing S26 ';
wherein,
searching for a tolerance error for the transmittance;
s25 ', let N = N +1, execute S21 ', if the determination of S22 ' is yes, and if there is a value M such that S24 ' is determined yes, execute S25 '; otherwise, the N value output by the S22 'and the M value output by the S24' in the previous round are the optimal N value and M value;
s26 ', making N = N-1, executing S21', if the judgment of S22 'is yes, and M value exists, so that the judgment of S24' is yes, then using the N value output by the S22 'and the M value output by the S24' as the optimal N value and M value; otherwise, S26' is executed until the optimum N and M values are obtained.
8. The method of designing and implementing a complex amplitude modulated super surface device as claimed in claim 6 or 7, further comprising:
and determining a theoretical complex amplitude distribution of the super-surface device, and selecting the unit structure with the provided complex amplitude modulation quantity closest to the unit structure from the M x N corresponding unit structures for each theoretical complex amplitude value, thereby forming the super-surface device.
9. The method of claim 6, wherein the method of designing and implementing a complex amplitude modulated super surface device is performed using micro-nano three-dimensional fabrication techniques.
10. The method of claim 9 wherein the super surface device is fabricated using a laser three-dimensional direct writing technique based on two-photon polymerization principle.
11. A complex amplitude modulated super surface device obtainable by a method according to any of claims 1 to 10.
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