Optical Vortices from Liquid Crystal Droplets

Brasselet, Étienne; Murazawa, Naoki; Misawa, Hiroaki; Juodkazis, Saulius

doi:10.1103/physrevlett.103.103903

Cited by 247 publications

(218 citation statements)

References 28 publications

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“…This expression reveals two contributions: a polarization dependent geometric phase, within the matrix, that stems from the spin-orbit coupling at the annular groove, and a factorized dynamic phase that arises due to the spiral twist of the structure [20]. Note, that for m out = m in = 0, T describes a pure spinorbit angular momentum transfer, conserving the total angular momentum [20,[30][31][32]. We can cast in a table these results in the form of summation rules for the OAM generated and transmitted through the membrane.…”

Section: By Rewriting the Polarization Coupling Term [E Inmentioning

confidence: 99%

Generating Far-Field Orbital Angular Momenta from Near-Field Optical Chirality

et al. 2013

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We demonstrate that nanostructures carefully designed on both sides of a thin suspended metallic membrane couple light into a chiral near field and transmit vortex beams through a central aperture that connects the two sides of the membrane. We show how far-field orbital angular momentum (OAM) indices can be tailored through nanostructure designs. We reveal the crucial importance of OAM selection rules imposed by the central aperture and derive OAM summation rules in perfect agreement with experimental data. PACS numbers:Structured light beams with phase or polarization singularities, have revealed unique optical properties with applications ranging from super-resolution imaging [1] to high-resolution sensing [2] and from particle micromanipulation [3] to quantum optics [4]. Currently, chiral nanostructures draw promising routes for enhancing singular optical signatures, thus providing extended control over new functionalities in metamaterial science [5] and biomimetics engineering [6,7]. Interestingly, while the connection between optics and chirality is well established for 3 dimensional (3D) chiral structures, the interaction of chiral light with 2D chiral objects is a topic of on-going debate [8][9][10], with strong potential in physical chemistry for chirality enhancement in the near field [11][12][13].Recently, singular optical effects have been discussed in the near field, in particular in relation to chiral surface plasmon (SP) modes which have been shown to carry orbital angular momentum (OAM) [14][15][16][17]. But until now, singular SP modes and associated spin-orbit coupling have only been probed in the near field [18][19][20]. Studies on plasmonic beaming with OAM have been scarce [21,22] and the relation between near-field chirality and OAM in the far field was never addressed.In this Letter, we demonstrate that nanostructures carefully designed on both sides of a thin suspended membrane lead to tailoring optical OAM in the far field. Single and double-sided plasmonic structures consisting of concentric grooves periodically spaced from a central subwavelength aperture -so called plasmonic bull's eye (BE)-have shown extraordinary optical transmission and beaming effects [23,24]. Yet, the OAM behaviour of these structures was not discussed. This Letter presents a comprehensive analysis of the OAM transfer during plasmonic in-coupling and out-coupling by chiral nanostructures at each side of a membrane, stressing in particular the role of a back-side structure in generating vortex beams as e iℓϕ with tunable OAM indices ℓ. With such membranes, we achieve propagating beams carrying OAM up to |ℓ| = 8. Moreover we reveal and analyze the fundamental role of the central aperture in the system's OAM generation through specific selection rules.Our device consists of a suspended thin (h ∼ 300 nm) metallic membrane, fabricated by evaporating a metal film over a poly(vinyl formal) resine supported by a transmission electron microscopy copper grid. After evaporation, the resine is removed using a focused ion-bea...

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Section: By Rewriting the Polarization Coupling Term [E Inmentioning

confidence: 99%

Generating Far-Field Orbital Angular Momenta from Near-Field Optical Chirality

et al. 2013

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“…4(b). These results are obtained following the Stokes polarimetry procedure used in [11], namely, È ¼ arctan½ðI þ45 À I À45 Þ=ðI 0 À I 90 Þ , where I refers to the transverse spatial intensity distribution of the linearly polarized component of the output light field oriented at an angle from the x axis.…”

Section: H Y S I C a L R E V I E W L E T T E R Smentioning

confidence: 99%

“…In particular, the realization of micron-size spin-orbit optical vortex generators has been reported using nematic droplets [11]. However, so far, natural [11], electrical [12], optical [13,14], or electro-optical [15] strategies based on the spontaneous creation of defects all correspond to the case jsj ¼ 1. Following Eq.…”

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confidence: 99%

Manipulating the Orbital Angular Momentum of Light at the Micron Scale with Nematic Disclinations in a Liquid Crystal Film

2013

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We report on the experimental manipulation of the orbital angular momentum of light by exploiting a kind of topological defects that spontaneously appear in nematics-disclinations-as microscopic optical spin-orbit interfaces whose operating wavelength can be controlled electrically. Using six different kinds of disclinations, we demonstrate the efficient generation of both scalar and vectorial singular light beams with a broad topological diversity from a fundamental Gaussian beam.

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“…The realization of higher-order masks with even topological charges > 2 [5] that are desirable for future extremely large telescopes [15] is another manufacturing challenge. Since the basic technological bottleneck can be identified as the manmade technology itself, a nature-assisted approach would likely open a novel generation of vortex masks.Various kinds of spontaneously formed nematic liquid crystal topological defects have been previously demonstrated to behave as natural [16,17] or field-induced [18][19][20] vectorial optical vortex generators with even charge | | = 2 and optimal beam shaping characteristics. Optical vortex masks realized without the need for a machining technique have also been obtained from other mesophases such as cholesteric [21] and smectic [22] liquid crystals, but at the expense of efficiency.…”

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Vortex coronagraphy from self-engineered liquid crystal spin-orbit masks

Aleksanyan

Brasselet

2016

Opt. Lett.

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We report on a soft route toward optical vortex coronagraphy based on self-engineered electrically tunable vortex masks made of liquid crystal topological defects. These results suggest that a natureassisted technological approach to the fabrication of complex phase masks could be useful in optical imaging whenever optical phase singularities are at play.The observation of faint objects near a bright source of light is a basic challenge of high-contrast imaging techniques such as the quest for extrasolar planets in astronomical imaging. This has led to the development of instruments called coronagraphs, which combine the high extinction of stellar light and the high transmission of a low-level signal at small angular separation. Stellar coronagraphy was initiated more than 80 years ago when Lyot studied solar corona without an eclipse by selective occultation of sunlight, placing an opaque disk in the focal plane of a telescope [1]. On the other hand, phase mask coronagraphs offer good performance for the observation of point-like sources. An early version consisted of using a disk π-phase mask [2] whose chromatic drawback arising from discrete radial phase step was solved a few years later by incorporating discrete radial [3] or azimuthal [4] phase modulation to the original design. Later on, continuous azimuthal phase ramps improved the approach [5,6] and led to the advent of optical vortex coronagraphy.Vortex coronagraphs rely on the selective peripheral redistribution of on-axis light outside an area of null intensity at the exit pupil plane of the instrument, which is done by placing a spiraling phase mask in the Fourier plane characterized by a complex transmittance of the form exp(i φ), where the charge is an even integer and φ is the usual azimuthal angle in the transverse plane. This enables optimal on-axis rejection of light by placing an iris (called Lyot stop) at the exit pupil plane, while the off-axis weak signal is almost unaffected for an angular separation larger than the diffraction limit [7]. There are two families of optical vortex phase masks that rely on the scalar (phase) and vectorial (polarization degree of freedom) properties of light. The former case refers to the helical shaping of the wavefront from a refractive phase mask, whereas the latter one exploits the polarization properties of space-variant birefringent optical elements. Indeed, inhomogeneous anisotropic phase masks endowed with azimuthal optical axis orientation of the form ψ(φ) = mφ with m half-integer and associated with half-wave birefringent phase retardation lead to a vortex mask of charge = 2σm for incident on-axis circularly polarized light beam with helicity σ = ±1, as originally shown in [8] using form birefringence (subwavelength grating of dielectric materials) and, in [9], using true birefringence.The achromatic features of the vectorial option versus its scalar counterpart [10,11] have eventually led to equip state-of-the-art large instruments such as Keck, Subaru, Hale, Large Binocular Telescope, and Very Larg...

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Optical Vortices from Liquid Crystal Droplets

Cited by 247 publications

References 28 publications

Generating Far-Field Orbital Angular Momenta from Near-Field Optical Chirality

Generating Far-Field Orbital Angular Momenta from Near-Field Optical Chirality

Manipulating the Orbital Angular Momentum of Light at the Micron Scale with Nematic Disclinations in a Liquid Crystal Film

Vortex coronagraphy from self-engineered liquid crystal spin-orbit masks

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