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WO2016168173A1 - Métasurfaces diélectriques optiques à longueurs d'onde multiples - Google Patents

Métasurfaces diélectriques optiques à longueurs d'onde multiples Download PDF

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Publication number
WO2016168173A1
WO2016168173A1 PCT/US2016/027086 US2016027086W WO2016168173A1 WO 2016168173 A1 WO2016168173 A1 WO 2016168173A1 US 2016027086 W US2016027086 W US 2016027086W WO 2016168173 A1 WO2016168173 A1 WO 2016168173A1
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scattering elements
wavelength
substrate
lens
different
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PCT/US2016/027086
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English (en)
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Ehsan ARBABI
Amir Arbabi
Andrei Faraon
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California Institute Of Technology
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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
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/30—Polarising elements
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/42—Coupling light guides with opto-electronic elements
    • G02B6/4201—Packages, e.g. shape, construction, internal or external details
    • G02B6/4204—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms
    • G02B6/4215—Packages, e.g. shape, construction, internal or external details the coupling comprising intermediate optical elements, e.g. lenses, holograms the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers

Definitions

  • the present disclosure relates to optical scattering. More particularly, it relates to multi- wavelength optical dielectric metasurfaces.
  • Fig. 1 illustrates an example of a distorted focus compared to a non distorted focus at multiple wavelengths.
  • Fig. 2 illustrates a metasurface lens divided into eight sectors.
  • Fig. 3 depicts an SEM micrograph of a fabricated device.
  • Figs. 4-6 illustrate simulated intensity patterns.
  • Fig. 7 illustrates a lens with alternating posts.
  • Fig. 8 illustrates the normalized optical intensity plotted in the axial plane of the double- wavelength lens of Fig. 7.
  • Fig. 9 illustrates the normalized intensity profile in the axial and focal planes.
  • Fig. 10 illustrates an example of elliptical scattering elements.
  • Fig. 11 illustrates corrections to chromatic aberrations.
  • Fig. 12 illustrates an exemplary metasurface design.
  • Fig. 13 illustrates microscope images of exemplary structures.
  • Fig. 14 illustrates exemplary measurement results.
  • Fig. 15 illustrates an exemplary measurement setup.
  • Fig. 16 illustrates exemplary simulation results.
  • a structure comprising: a substrate; a first plurality of scattering elements on the substrate, the first plurality of scattering elements having first geometrical dimensions for the scattering elements; and a second plurality of scattering elements on the substrate, the second plurality of scattering elements having second geometrical dimensions for the scattering elements, the second geometrical dimensions being different from the first geometrical dimensions.
  • a method comprising: providing a substrate; fabricating a first plurality of scattering elements on the substrate according to first geometric dimensions, to scatter light at a first wavelength; and fabricating a second plurality of scattering elements on the substrate according to second geometric dimensions, to scatter light at a second wavelength, wherein the first geometric dimensions are different from the second geometric dimensions, and the first wavelength is different from the second wavelength.
  • Optical metasurfaces are structures with subwavelength thicknesses relative to the electromagnetic wavelength range the structures are meant to operate in. In other words, optical metasurfaces are thinner than a wavelength and can therefore shape the amplitude, phase, and polarization of electromagnetic beams.
  • Dielectric metasurfaces are arrays of scattering elements having a high refractive index, the array being on a low refractive index material substrate. Dielectric metasurfaces have shown high versatility and efficiency in various optical functionalities, see Refs. [1-5]. One drawback of these metasurfaces is their limited bandwidth, which stems from their high diffractive chromatic aberration. Therefore, these dielectric metasurfaces are mostly limited to operating at a single wavelength, or close to a single wavelength, and cannot be used towards applications needing multiple wavelength capabilities. In the present disclosure, methods are disclosed for designing multi -wavelength metasurfaces.
  • Dielectric metasurfaces are composed of a large number of scatterers placed on two dimensional lattices; the scattering phases and amplitudes for the scattering elements are tailored and designed to achieve a desired functionality.
  • methods are disclosed for designing multi -wavelength metasurfaces. Some embodiments of the present disclosure are based on dividing the lattice into two or more sub-lattices, and designing the scatterers on each sub-lattice for operation at a specific wavelength. As shown in the present disclosure via examples, these embodiments describe metasurfaces working at two or more wavelengths, simultaneously. In other embodiments, varying several degrees of freedom in the design of the geometry of the scatterers can achieve the desired scattering response at different wavelengths.
  • metasurfaces are nanostructured devices composed of arrays of subwavelength scatterers (or meta-atoms) that manipulate the wavefront, polarization, or intensity of light. Similarly to other diffractive optical devices, metasurfaces can suffer from significant chromatic aberrations that limit their bandwidth.
  • methods for designing multi -wavelength metasurfaces are described, using unit cells with multiple meta- atoms, or meta-molecules. Transmissive lenses with efficiencies as high as, for example, 72% and numerical apertures as high as, for example, 0.46 simultaneously operating at 915 nm and 1550 nm are possible. With proper scaling, these devices can be used in applications where operation at distinct known wavelengths is required, like various fluorescence microscopy techniques.
  • chromatic dispersion mainly manifests itself through a significant change of focal length as a function of wavelength, see Ref. [18]. This change is schematically shown in Fig. 11 (1105), where different wavelengths focus at different spatial locations. Fig. 11 also illustrates a metasurface lens corrected to have the same focal distance at a few wavelengths (1110). To better understand the underlying reasons for this chromatic dispersion, it is possible to consider a hypothetical aspherical metasurface lens. The lens is composed of different meta- atoms which locally modify the phase of the transmitted light to generate the desired wavefront.
  • ⁇ is the wavelength
  • L is an effective parameter associated with the meta-atoms that controls the phase (L can be an actual physical parameter or a function of physical parameters of the meta-atoms).
  • L can be an actual physical parameter or a function of physical parameters of the meta-atoms).
  • L can be an actual physical parameter or a function of physical parameters of the meta-atoms.
  • the lens is designed to focus light at ⁇ 0 (1 1 15) to a focal distance fo, and its phase profile in all Fresnel zones matches the ideal phase profile at this wavelength.
  • the phase profile of the lens in the first Fresnel zone follows the desired ideal profile needed to maintain the same focal distance (1 1 15). However, outside the first Fresnel zone, the actual phase profile of the lens deviates substantially from the desired phase profile. Due to the jumps at the boundaries between the Fresnel zones, the actual phase of the lens at ⁇ is closer to the ideal phase profile at ⁇ 0 than the desired phase profile at ⁇ ⁇ .
  • the effective meta-atom parameter L is plotted as a function of distance to the center of the lens p.
  • the chromatic dispersion of metasurface lenses mainly stems from wrapping the phase, and the dependence of the phase on only one effective parameter (e.g. L) whose value undergoes sudden changes at the zone boundaries.
  • L effective parameter
  • using two parameters to control metasurface phase at two wavelengths can resolve this issue, and enable lenses with the same focal lengths at two different wavelengths.
  • several optical metasurfaces designs suffer from high chromatic aberrations because of their principle of operation based on diffraction. For instance, a metasurface lens will focus optical waves with different wavelengths to different focal points. Furthermore, wavelengths other than the wavelength at which the metasurface is designed to operate will a distorted focus. An example of distorted focus can be seen, for example, in Fig.
  • Fig. 1 shows several different wavelengths (110) transmitted through a substrate (115), for example a transparent substrate. Subsequently, the metasurface (125) will scatter the electromagnetic radiation with a distorted focus (120). In other words, each wavelength will focus at a different spatial position.
  • the metasurfaces described in the present disclosure can focus multiple wavelengths at the same spatial position (130).
  • a typical metasurface lens focuses lights of different wavelengths to different focal points, while a multi- wavelength metasurface focuses light of specific wavelengths to the same focal point.
  • Fig. 2 illustrates a metasurface lens divided into eight sectors (205). Each of the eight sectors can be designed to focus a specific wavelength. For example, in Fig. 2 four sectors (210) are designed for wavelength of 1550 nm, while the other four sectors (215) are designed for 775 nm. In Fig.
  • a zoomed-in view (220) of the center of the metasurface lens is also visible.
  • the lens in Fig. 2 is designed with cylindrical posts of a-Si, amorphous Si, as scattering elements on a glass substrate.
  • the scattering elements, or posts are 938 nm tall, and have different diameters to generate different phases. In other embodiments, different geometries and height may be used for the scattering elements.
  • the present disclosure describes double-wavelength lenses based on a dielectric metasurface structure described in Ref. [1].
  • the high index material used in these embodiments can be, for example, a-Si with a thickness of 938 nm, on a fused silica substrate.
  • a lens can have a 100 ⁇ diameter and a 50 ⁇ focal distance. The total lens area can be divided into multiple sectors.
  • Fig. 2 shows a lens designed for 1550 nm and 775 nm with eight sectors (four for each wavelength), while Fig. 3 shows a SEM micrograph of a fabricated device according to this example.
  • cylindrical a-Si scatterers on a fused silica substrate can be seen, having two diameters (305, 310). Each of the diameters scatters light at a specific wavelength, such as 1550 and 775 nm.
  • Figs. 4-6 The simulated intensity patterns for the structure of Fig. 3, in the focal and axial planes, are shown in Figs. 4-6 for both wavelengths.
  • An efficiency higher than 40 % is expected at both wavelengths.
  • Efficiency is defined as the ratio of power focused to an area of 5 ⁇ ⁇ 5 ⁇ around the focal point, to the total power of the beam incident upon the lens. This performance can be understood by the fact that only around 50 % of the incident beam power is incident on parts of the metasurface designed for that specific wavelength. Increasing the number of sectors can improve the focus shape by removing the division effects, but can result in a lower efficiency as the edge effects become more important.
  • Fig. 4 illustrates the simulated intensity in the focal plane for 775 (405) and 1550 (410) nm, for a lens with 8 sectors.
  • Fig. 5 illustrates the simulated intensity in the axial plane for 775 (505) and 1550 (510) nm, for a lens with 8 sectors.
  • Fig. 6 illustrates the simulated intensity in the focal plane for 775 (605) and 1550 (610) nm, for a lens with 14 sectors.
  • the optical intensity is plotted at the focal plane of a double-wavelength lens. The resultant efficiency is reduced to about 35 % in this example.
  • a double wavelength lens can be designed by alternatingly assigning the posts in each row of the lattice to one of each of two wavelengths, as visible in Fig. 7.
  • Fig. 7 illustrates a zoomed detail (705) view of the area (710).
  • a double wavelength metasurface is realized by alternating the operating wavelength in each row of the lattice.
  • the zoomed-in view (710) of the metasurface shows the large size difference between posts on each row relative to its adjacent rows.
  • the smaller size rows are designed for the shorter wavelength, while the larger ones are designed for the longer wavelength.
  • the rows can be circular rows, progressively radiating outward from the center of a circular lens.
  • a lens can be realized with a diameter of 300 ⁇ and a focal distance of 400 ⁇ , for operation at the 1550 nm and 775 nm wavelengths. Normalized simulated field intensities for this exemplary lens are shown in Figs. 8-9. An efficiency of about 27 % is expected in both wavelengths for this case.
  • Fig. 8 illustrates the normalized optical intensity plotted in the axial plane of the double- wavelength lens of Fig. 7, for 775 nm (805), and 1550 nm (810).
  • Fig. 9 illustrates the normalized intensity profile in the focal plane (905) around the focal point, showing a good focus pattern for both wavelengths, 775 nm (915) and 1550 nm (920).
  • Fig. 9 also illustrates the normalized intensity plotted in the axial plane (910), showing an equal focal distance of 400 ⁇ for both wavelengths, 775 nm (925) and 1550 nm (930), as designed.
  • the design of multi -wavelength metasurfaces uses extra degrees of freedom in the geometry of the scattering elements to independently control the phase profiles of the metasurfaces at different wavelengths.
  • elliptical high contrast scatterers can be used instead of cylindrical ones.
  • the elliptical elements will have two control parameters (i.e. two ellipse diameters) instead of one (radius of cylindrical posts). Therefore, the elliptical elements have one additional degree of freedom compared to the cylindrical elements.
  • the additional degrees of freedom the phases imparted on two polarizations of light (such as vertical and horizontal) can be controlled almost independently.
  • Fig. 10 illustrates an example of elliptical scattering elements (1005, 1010), with a schematic drawing of an elliptical scatterer.
  • the elliptical scattering elements can control the polarization directions of light in two perpendicular axis, x-polarized and y-polarized light, with respect to the ellipsoidal cross section.
  • Fig. 10 comprises a SEM micrograph of fabricated a-Si elliptical scatterers (1015).
  • the orientation of each scatterer, as visible in Fig. 10 can be designed according to the required specification of a lens, to scatter light at different wavelengths.
  • metasurfaces In addition to designing metasurfaces to have the same functionality at different wavelengths, the methods described above can be used to design a metasurface for distinct desired functionalities at different wavelengths. For instance, a lens that has two different (but desired) focal distances at two different wavelengths, or a lens that is converging at one wavelength, and diverging at another wavelength.
  • the scattering elements assigned to each wavelength have different geometric dimensions, and may have different spacing.
  • the consecutive circular rows have decreasing thickness radiating outward from the center of the lens.
  • the sectors assigned to each type of scattering elements are octaves in a circular lens.
  • three or more types of scattering elements may be employed to scatter light at three or more different wavelengths.
  • the scattering elements have a height between 100 and 1000 nm.
  • the metasurface platform described in the present disclosure is based on amorphous silicon (a-Si) nano-posts on a fused silica substrate, see Fig. 12 (1205).
  • the nano-posts can be placed on the vertices of a hexagonal lattice, or equally in the centers of the hexagons (1210), and locally sample the phase to generate the desired phase profile, see Ref. [8].
  • the transmission phase of a nano-post can be controlled by varying its diameter. The height of the posts can be chosen such that at a certain wavelength the whole 2 ⁇ phase shift is covered, while keeping the transmission amplitude high.
  • a unit cell consisting of four different nano-posts (1210) can be chosen because it has more parameters to control the phases at two wavelengths almost independently.
  • one type of post (1215) may have a larger diameter than other posts (1220).
  • meta-molecules As molecules consisting of multiple atoms form the units of more complex materials, these unit cells with multiple meta-atoms can be termed meta-molecules.
  • the meta-molecules can also form a periodic lattice (in this example hexagonal), and effectively sample the desired phase profiles simultaneously at two wavelengths. The lattice is subwavelength at both wavelengths of interest; therefore, the non-zero diffraction orders are not excited.
  • the four nano-posts of the exemplary meta-molecule of Fig. 12 can each have different diameters and distances from each other. However, to make the design process more tractable, in some embodiments three of the four nano-posts have the same diameter and the fourth post has a diameter D 2 .
  • each meta-molecule can have two parameters, D and D 2 , to control the phases at two wavelengths.
  • the two wavelengths can be 1550 nm and 915 nm, because of the availability of lasers at these wavelengths.
  • a periodic array of meta-molecules was simulated to find the transmission amplitude and phase as shown in (1230).
  • and ⁇ 2 ) are plotted as functions of Di and D 2 in (1235) and (1240).
  • E and ⁇ 2
  • the corresponding transmission amplitudes for the chosen meta-molecules are plotted in (1250), and show this automatic avoidance of low transmission meta-molecules.
  • the desired transmission phases of the lens are sampled at the lattice points at both wavelengths resulting in a ⁇ ) pair at each lattice site.
  • values of the two post diameters can be found for each lattice point.
  • the values of the two diameters are limited by D ⁇ + D 2 ⁇ a. In this example, a minimum value of 50 nm can be set for the gaps between the posts to facilitate the metasurface fabrication.
  • a double wavelength aspherical lens can be designed using the exemplary platform described above, to operate at both 1550 nm and 915 nm.
  • the lens has a diameter of 300 ⁇ and focuses the light emitted from single mode fibers at each wavelength to a focal plane 400 ⁇ away from the lens surface (the corresponding paraxial focal distance is 286 ⁇ , thus the numerical aperture is 0.46).
  • the exemplary lens was fabricated using standard nanofabrication techniques: a 718-nm-thick layer of a-Si was deposited on a fused silica substrate, the lens pattern was generated using electron beam lithography and transferred to the a-Si layer using aluminum oxide as a hard mask.
  • Optical (1305) and scanning electron microscope (1310, 1315) images of the lens and nano-posts are shown in Fig. 13.
  • the fabricated metasurface lens was illuminated by light emitted from the end facet of a single mode fiber, and the transmitted light intensity was imaged at different distances from the lens using a custom built microscope.
  • Fig. 14 (1405) and (1410) show the intensity profiles in the focal plane measured at 915 nm and 1550 nm, respectively.
  • the measured full width at half maximum (FWFDVI) is 1.9 ⁇ at 915 nm, and 2.9 ⁇ at 1550 nm.
  • the intensity measured at the two axial plane cross sections is plotted in (1415) and 1420) for the two wavelengths. A nearly diffraction limited focus is observed in the measurements, and no other secondary focal points with comparable intensity is seen.
  • a lens designed with the same method and based on the same metasurface platform is simulated using finite difference time domain (FDTD) method with a freely available software (MEEP), see Ref. [27].
  • FDTD finite difference time domain
  • MEEP freely available software
  • Fig. 14, (1425) and (1430) show the simulated focal plane intensity of the lens at 915 nm and 1550 nm, respectively.
  • the simulated FWFDVI is 1.9 ⁇ at 915 nm and 3 ⁇ at 1550 nm, both of which are in accordance with their corresponding measured values.
  • the simulated intensity distributions in the axial cross section planes, which are shown in (1435) and (1440) demonstrate only one strong focal point.
  • the focusing efficiency was found to be 32% at 915 nm, and 73% at 1550 nm.
  • the difference in the simulated and measured efficiencies can be attributed to fabrication imperfections and measurement artifacts.
  • the efficiency at 915 nm is found to be lower than what expected both in measurement and FDTD simulation. While the average power transmission of the selected meta-molecules is about 73%) as calculated from (1435), the simulated focusing efficiency is about 32%. To better understand the reasons for this difference, two blazed gratings with different angles were designed and simulated for both wavelengths using the same meta-molecules. It is observed that for the gratings (that are aperiodic), a significant portion of the power is diffracted to other angles both in reflection and transmission. Additionally, the power lost into diffractions to other angles is higher for the grating with larger deflection angle. The main reason for the large power loss to other angles is the relatively large lattice constant.
  • the chosen lattice constant of a 720 nm is just slightly smaller than 727 nm, the lattice constant at which the first-order diffracted light starts to propagate in the glass substrate for a perfectly periodic structure.
  • the lower transmission of some meta-molecules reduces the purity of the plane wave wavefronts diffracted to the design angle.
  • the desired phase profile of high numerical aperture lenses cannot be sampled at high enough resolution using large lattice constants. Therefore, as shown in this work, a lens with a lower numerical aperture has a higher efficiency.
  • the lattice constant is bound by the geometrical and fabrication constraint: + D 2 + 50nm ⁇ a, hence the smallest value of D + D 2 that gives full phase coverage at the longer wavelength sets the lower bound for the lattice constant.
  • This limit can usually be decreased by using taller posts, however, that would result in a high sensitivity to fabrication errors at the shorter wavelength.
  • the lattice constant can also be smaller if less than the full 2 ⁇ phase shift is used at 1550 nm (thus lowering efficiency at 1550 nm).
  • the exemplary approach presented above cannot be directly used to correct for chromatic dispersion over a continuous bandwidth; the multi -wavelength lenses still have chromatic dispersion similarly to normal metasurface lenses in narrow bandwidths around the corrected wavelengths.
  • the meta-atoms should independently control the phase at two very close wavelengths. High quality factor resonances must be present for the meta-atom phase to change rapidly over a narrow bandwidth, and such resonances will result in high sensitivities to fabrication errors that would make the metasurface impractical.
  • the meta-molecule platform described in the present disclosure to correct for chromatic aberration at specific wavelengths, can also be used for applications where different functionalities at different wave- lengths are desired. For instance, it can be used to implement a lens with two given focal distances at two wavelengths, or a lens converging at one wavelength and diverging at another wavelength. Multi -wavelength operation is necessary in various microscopy applications where fluorescence is excited at one wavelength and collected at another. In the example above, only two of the degrees of freedom of the meta-molecules were used, but increased functionalities at more than two wavelengths can be achieved by making use of all the degrees of freedom. Operation at more than two wavelengths enables applications in color display technologies or more complex fluorescence imaging techniques.
  • the paraxial focal distance of the two lenses were calculated to be 286 ⁇ and 495 ⁇ for the lenses that focus light from the fiber to 400 ⁇ and 1000 ⁇ respectively, by fitting a parabola to the phase profiles of the lenses.
  • the corresponding numerical apertures can then found to be 0.46 and 0.29 for the two lenses.
  • the perfect phase mask (that also served as the goal phase profile for the designed devices) was calculated from the illuminating field and the aspherical desired phase profile using the method described Ref. [8].
  • the illuminating field was calculated by propagating the output fields of single mode fibers at each wavelength using plane wave expansion (PWE) method up to the metasurface layer.
  • PWE plane wave expansion
  • the perfect phase mask was then applied to the field, and the result was propagated using the PWE method to the focal point.
  • the diffraction limited FWHM was then calculated from the intensity profile at the focal plane.
  • a 718-nm-thick hydrogenated a-Si layer was deposited on a fused silica substrate using the plasma enhanced chemical vapor deposition (PECVD) technique with a 5% mixture of silane in argon at 200 ° C.
  • PECVD plasma enhanced chemical vapor deposition
  • a Vistec EBPG5000+TM electron beam lithography system was used to define the metasurface pattern in the ZEP-520ATM positive resist (about 300 nm, spin coated at 5000 rpm for 1 min). The pattern was developed in a resist developer for 3 minutes (ZED-N50 TM from Zeon ChemicalsTM).
  • a fiber coupled semiconductor laser with a single mode fiber with an angled polished connector was used for illumination. Fiber tip angle was adjusted to correct for the angled connector cut.
  • a calibration sample with known feature sizes was measured to find the pixel-size transferred to the object plane. The objective was moved with a translation stage to image different planes around the focus.
  • the plotted axial plane intensities are upsampled 2: 1 in the axial direction (4 ⁇ adjacent measurement planes distance to 2 ⁇ ) to achieve a smoother graph.
  • a 20-//m-diameter pinhole was placed in the focal plane of the metasurface lens to only let the focused light pass through.
  • the pinhole was made by wet etching a 20 ⁇ hole in a thick layer of chrome deposited on a fused silica substrate.
  • a power meter Thin-PM100DTM with photodetector head Thorlabs S122CTM
  • the efficiency was calculated as the ratio of these two powers.
  • the reported measured efficiency is therefore a lower bound on the actual efficiency as it does not include reflection from the substrate, and two reflections from the two sides of the pinhole glass substrate.
  • a similar setup was used for measurements at 1550: a tunable 1550 nm laser (Photonetics Tunics-PlusTM) was used with a single mode fiber for illumination. The same 100X objective was used with a 20 cm tube lens (Thorlabs AC254-200- C-MLTM) to image the intensity in the object plane to a camera (Digital CamIR 1550TM by Applied Scintillation TechnologiesTM). The camera has a significantly non-uniform sensitivity for different pixels which leads to high noise level of the images captured by the camera.
  • the nonphysical high frequency noise of the images was removed numerically to reduce the noise in the axial intensity patterns.
  • the intensity pattern was also upsampled in the axial direction from the actual 4 ⁇ distance between adjacent measurement planes, to 2 ⁇ to achieve a smoother intensity profile.
  • the focal plane of the lens was imaged using the microscope to a photodetector.
  • a 2 mm iris in the image plane (corresponding to 20 ⁇ in the object plane) was used to limit the light reaching the photodetector.
  • the input power was measured by imaging the fiber facet to the photodetector using the same setup and without the iris. The efficiency was obtained by dividing the focused power by the input power.
  • the lengths are chosen such that the grating phases at 915 nm and 1550 nm are both almost repeated after the chosen lengths (1605).
  • Periodic boundary conditions were set at the edges (1610).
  • An x- polarized plane-wave normally incident from the fused silica side was used as excitation in both simulations, and the transmitted and reflected electric and magnetic field intensities were calculated about a wavelength apart from the meta-molecules.
  • the transmitted fields were further propagated using a plane wave expansion program, and the resulting fields in an area of length 30 ⁇ around the center can be seen in (1615) and (1620) for 5 degree and 20 degree gratings, respectively.
  • the field distributions outside of the areas shown here look similar to the ones shown in Fig. 16.
  • Fig. 15 illustrates exemplary measurement setups.
  • the measurement setup used to capture the focus pattern and the intensity distribution in different planes around focus is shown in (1505).
  • the laser source (1510), fibers (1530), objective lens (1522), tube lens (1515), and camera (1525) were different in 915 nm and 1550 nm measurements of the metasurface (1520).
  • the measurement setup for measuring the efficiency of the lenses at 915 nm using a 20 ⁇ pinhole (1545) in the focal plane is illustrated in (1535).
  • the setup for measuring focusing efficiency of the lens at 1550 nm using a 2 mm iris (1540) in the image plane of a 100X microscope is illustrated in (1555).
  • An optical power meter (1550) and mirror (1560) are also used with the iris.
  • the first plurality of scattering elements are each located at a center of a respective hexagon in a first plurality of hexagons and the second plurality of scattering elements are each located at a center of a respective hexagon of a second plurality of hexagons, wherein the first and second plurality of hexagons are arranged in a single hexagonal two-dimensional lattice and at least six hexagons of the second plurality of hexagons surround at least one hexagon of the first plurality of hexagons.

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Abstract

L'invention concerne des structures pour disperser de la lumière à de multiples longueurs d'onde. Des éléments de dispersion sont fabriqués avec différentes dimensions et dispositions géométriques, afin de disperser ou focaliser de la lumière à la même distance focale pour chaque longueur d'onde, ou à des distances focales différentes, selon l'application souhaitée. Des éléments de dispersion peuvent être circulaires ou elliptiques, de façon à permettre une dispersion dépendant de la polarisation. Les éléments peuvent avoir des orientations différentes afin de disperser de la lumière à partir de multiples longueurs d'onde à la longueur focale souhaitée.
PCT/US2016/027086 2015-04-14 2016-04-12 Métasurfaces diélectriques optiques à longueurs d'onde multiples WO2016168173A1 (fr)

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EP3451027A1 (fr) * 2017-09-01 2019-03-06 Thomson Licensing Dispositif optique capable de fournir au moins deux fonctions optiques différentes
WO2019103762A3 (fr) * 2017-06-19 2019-07-04 President And Fellows Of Harvard College Méta-optique multicouche à topologie optimisée
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US11906698B2 (en) 2017-05-24 2024-02-20 The Trustees Of Columbia University In The City Of New York Broadband achromatic flat optical components by dispersion-engineered dielectric metasurfaces
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