Extraordinary light focusing and Fourier transform properties of gradient-index metalenses

Ma, Chaoqun; Escobar, Marco Antonio Camacho; Liu, Zhaowei

doi:10.1103/physrevb.84.195142

Cited by 37 publications

(32 citation statements)

References 40 publications

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“…Various types of phase compensation mechanism have been proposed for focusing plane waves in metalenses [18][19][20] . The underlying design principle is to satisfy the phase matching condition to constructively bring plane waves from air into deep subwavelength focus inside the metamaterial.…”

Section: Principles Of the Metalensmentioning

confidence: 99%

“…The underlying design principle is to satisfy the phase matching condition to constructively bring plane waves from air into deep subwavelength focus inside the metamaterial. This can be accomplished by either geometric variations, such as plasmonic waveguide couplers (PWC) 18,[51][52][53] and shaped metamaterial-air interfaces 19,54 , or material refractive-index variations like gradient-index (GRIN) metamaterials 20 . For example, a PWC, composed of an array of specially designed non-periodic metalinsulator-metal waveguides, can turn non-flat wave-fronts at the metamaterial-PWC interface into flat ones at the PWC-air interface, thus matching the phase condition for realizing a deep subwavelength focus inside the metamaterial slab 18,51 .…”

Section: Principles Of the Metalensmentioning

confidence: 99%

“…Using transformation optics 55,56 , such geometry variations can be transformed to refractive-index variations within the material space, resulting in a GRIN metalens. Analogous to a conventional GRIN lens 57 , the designed permittivity profiles for a GRIN metalens gradually bring plane waves to a super-resolution focus inside the metamaterial 20,58 .…”

Section: Principles Of the Metalensmentioning

confidence: 99%

“…Inhomogeneous metamaterials have been utilized to focus light in the infrared 58,62 or surface waves 63 . The GRIN metalens, with appropriately designed permittivity profiles, was first investigated for its superresolution imaging, as well as its Fourier transform capabilities at optical wavelengths 20 . The hyperbolic permittivity profile, enabled by the use of silver nanowires grown in an alumina template, gradually converges a normally incident wave to a subdiffraction-limited focus inside the metamaterial (Fig.…”

Section: Principles Of the Metalensmentioning

confidence: 99%

“…super-resolving power and Fourier transform function, making them more like conventional lenses but with superior capabilities [18][19][20][21] .…”

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Hyperlenses and metalenses for far-field super-resolution imaging

2012

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The resolution of conventional optical lens systems is always hampered by the diffraction limit. Recent developments in artificial metamaterials provide new avenues to build hyperlenses and metalenses that are able to image beyond the diffraction limit. Hyperlenses project super-resolution information to the far field through a magnification mechanism, whereas metalenses not only super-resolve subwavelength details but also enable optical Fourier transforms. Recently, there have been numerous designs for hyperlenses and metalenses, bringing fresh theoretical and experimental advances, though future directions and challenges remain to be overcome.O ptical microscopy has revolutionized many fields such as microelectronics, biology and medicine. However, the resolution of a conventional optical lens system is always limited by diffraction to about half the wavelength of light. This diffraction barrier arises from the fact that subwavelength information from an object is carried by high spatial-frequency evanescent waves, which only exist in the near field. To overcome this diffraction limit, pioneering work has been carried out, including near-field scanning microscopy 1 , as well as fluorescence-based imaging methods 2,3 . These scanning-or random sampling-based nonprojection techniques achieve super-resolving power by sacrificing imaging speed, making them uncompetitive for dynamic imaging.Lens-based projection imaging remains the best option for high-speed microscopy. Immersion techniques have been proposed to enhance resolution, but they are limited by the low refractive indices of natural materials 4 . Emerging within the last decade, the fields of plasmonics and metamaterials provide solutions for engineering extraordinary material properties not found in nature, such as negative index of refraction 5,6 or strongly anisotropic materials 7,8 . This has provided tremendous opportunities for novel lens designs with unprecedented resolution 9 . Initiated by Pendry's seminal concept of the perfect lens 10 , a number of superlenses were demonstrated with resolving powers beyond the diffraction limit [11][12][13][14][15][16][17] . The optical superlens first achieved sub-diffraction-limited resolution by enhancing evanescent waves through a slab of silver 11 . As the evanescent-field enhancement is enabled by surface plasmon excitation, the subwavelength image is typically limited to the near field of the metal slab. However, the hyperlens-a metamaterial-based lens-can send super-resolution images into the far field by introducing a magnification mechanism. This has been considered as one of the most promising candidates for practical applications since its first demonstration in 2007 (refs 13,14). Recently, various other metamaterial-based lenses, that is, metalenses, have also been developed with both

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Section: Principles Of the Metalensmentioning

confidence: 99%

Section: Principles Of the Metalensmentioning

confidence: 99%

Section: Principles Of the Metalensmentioning

confidence: 99%

Section: Principles Of the Metalensmentioning

confidence: 99%

“…super-resolving power and Fourier transform function, making them more like conventional lenses but with superior capabilities [18][19][20][21] .…”

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confidence: 99%

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Hyperlenses and metalenses for far-field super-resolution imaging

2012

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Three‐Dimensional Super Lens Composed of Fractal Left‐Handed Materials

Wang

et al. 2013

Advanced Optical Materials

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The lens which can focus electromagnetic (EM) waves below the wavelength represents one of the most fundamental building blocks in the optical microscopy. However, the spatial resolution of conventional lenses is commonly confi ned to half of the illuminating wavelength due to the diffraction limits. A survey of state of the art indicates that an explosion of activities and efforts, both theoretical and experimental, have been devoted to overcome these limits, namely designing super lenses with better resolution. To date, several techniques are available, e.g., lenses fabricated by using left-handed (LH) bulk materials with negative refractive index (NRI), [1][2][3][4][5][6][7][8] LH transmission-line (TL) materials, [9][10][11][12][13][14][15][16][17][18][19][20] photonic crystals, [ 21 ] gradient-index materials, [22][23][24] chiral medium, [ 25,26 ] biocompatible material, [ 27 ] complementary V-shaped antennas, [ 28 ] near-fi eld plate, [ 29 ] acoustic metamaterial, [ 30 ] perovskites, [ 31 ] silver fi lm or layer, [32][33][34] dielectric elastomers [ 35 ] and even based on compensation mechanism. [ 36 ] Moreover, the progress of super lenses has been extended significantly from the original gigahertz (GHz) region to terahertz and even optical frequencies [32][33][34]37 ] via the excitation of surface plasmons.Among them, the LH material (LHM) lens, also termed as Veselago-Pendry lens, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] has intrigued an enormous and long-holding interest in science and engineering communities since Veselago and Pendry predicted in their seminal work [ 1,2 ] that lens made of LHM slab is able to overcome the conventional diffraction limits. This is especially true for the representative LH-TL lenses due to their low loss and small volume, because the lossy and thick LHM drastically deteriorates the evanescent-wave enhancement which contributes much to the sub-diffraction imaging. The physical mechanism for super resolution is that the LHM lens is not only capable of focusing the propagating waves emanating from the sources but also of amplifying the evanescent waves which restore useful information of sources and decay exponentially in vacuum. [ 10 ] However, the subwavelength imaging is achieved only when some strict requirements are fulfi lled. First, specifi c material parameters are required with the permeability μ eff = − μ 0 and permittivity ε eff = − ε 0 at the focusing frequency in order to make the matched impedance Z = Z 0 and refractive index n eff = −1, where Z 0 is the intrinsic impedance of the free space and μ 0 and ε 0 are the permeability and permittivity in free space. Second, electrically small dimensions of basic elements are required. Third, appropriate position for the focal spot and suffi ciently large transverse dimensions are required in addition to the aforementioned low loss and thin thickness.Although the LH-TL lenses are able to provide a decent resolution, most of them are restricted to the planar TLs which are constructed by peri...

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Meta‐Imaging: from Non‐Computational to Computational

Sihvola

2020

Advanced Optical Materials

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Metamaterials are artificial media composed of periodic/aperiodic subwavelength metal/dielectric structures (i.e., meta-atom). This class of media possess electromagnetic properties not present in the constituent materials and have yielded breakthrough electromagnetic phenomena. The capability of tailoring effective electric permittivity and magnetic permeability responses leads to a wide range of accomplishments, such as enhanced nonlinearity, [1] and electromagnetic cloak. [2] However, high losses, strong

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Extraordinary light focusing and Fourier transform properties of gradient-index metalenses

Cited by 37 publications

References 40 publications

Hyperlenses and metalenses for far-field super-resolution imaging

Hyperlenses and metalenses for far-field super-resolution imaging

Three‐Dimensional Super Lens Composed of Fractal Left‐Handed Materials

Meta‐Imaging: from Non‐Computational to Computational

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