Influence of atmospheric turbulence on optical communications using orbital angular momentum for encoding

May, 2012

Author(s): Mehul Malik, Malcolm O’Sullivan, Brandon Rodenburg, Mohammad Mirhosseini, Jonathan Leach, Martin P. J. Lavery, Miles J. Padgett, and Robert W. Boyd

Abstract:

“We describe an experimental implementation of a free-space 11-dimensional communication system using orbital angular momentum (OAM) modes. This system has a maximum measured OAM channel capacity of 2.12 bits/photon. The effects of Kolmogorov thin-phase turbulence on the OAM channel capacity are quantified. We find that increasing the turbulence leads to a degradation of the channel capacity. We are able to mitigate the effects of turbulence by increasing the spacing between detected OAM modes. This study has implications for high-dimensional quantum key distribution (QKD) systems. We describe the sort of QKD system that could be built using our current technology.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 20, Issue 12, pp. 13195-13200 (2012)
doi:10.1364/OE.20.013195


Nonimaging speckle interferometry for high-speed nanometer-scale position detection

March, 2012

Author(s): E. G. van Putten, A. Lagendijk, and A. P. Mosk

Abstract:

“We experimentally demonstrate a nonimaging approach to displacement measurement for complex scattering materials. By spatially controlling the wavefront of the light that incidents on the material, we concentrate the scattered light in a focus on a designated position. This wavefront acts as a unique optical fingerprint that enables precise position detection of the illuminated material by simply measuring the intensity in the focus. By combining two fingerprints we demonstrate position detection along one in-plane dimension with a displacement resolution of 2.1 nm. As our approach does not require an image of the scattered field, it is possible to employ fast nonimaging detectors to enable high-speed position detection of scattering materials.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 37, Issue 6, pp. 1070-1072 (2012)
doi:10.1364/OL.37.001070


Fabrication of three-dimensional electrospun microstructures using phase modulated femtosecond laser pulses

January, 2012

Author(s): Nathan J. Jenness, Yiquan Wu, Robert L. Clark.

Abstract:

“Electrospun polycaprolactone nanofibers were selectively ablated to form microstructures via the phase modulation of femtosecond laser beams. Ablation width (1–15 μm) and depth (15–110 μm) resolution were dependent upon the selection of pulse energy and microscope objective. Because phase modulation shapes light in a maskless fashion, desired templates were digitally created and physically transferred to electrospun mats within a matter of minutes. Several microarchitectures were formed in parallel by dividing pulse energy between multiple foci, substantially increasing throughput. The data presented herein demonstrates that phase-based laser ablation can be used to rapidly shape and tailor electrospun mats in three dimensions.”

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Publication: Materials Letters, (subscription required)

Issue/Year/DOI: Materials Letters, Volume 66, Issue 1, 1 January 2012, Pages 360–363
doi:10.1016/j.matlet.2011.09.015


Photo-designed terahertz devices

October, 2011

Author(s): Takanori Okada & Koichiro Tanaka

Abstract:

“Technologies are being developed to manipulate electromagnetic waves using artificially structured materials such as photonic crystals and metamaterials, with the goal of creating primary optical devices. For example, artificial metallic periodic structures show potential for the construction of devices operating in the terahertz frequency regime. Here we demonstrate the fabrication of photo-designed terahertz devices that enable the real-time, wide-range frequency modulation of terahertz electromagnetic waves. These devices are comprised of a photo-induced, planar periodic-conductive structure formed by the irradiation of a silicon surface using a spatially modulated, femtosecond optical pulsed laser. We also show that the modulation frequency can be tuned by the structural periodicity, but is hardly affected by the excitation power of the optical pump pulse. We expect that our findings will pave the way for the construction of all-optical compact operating devices, such as optical integrated circuits, thereby eliminating the need for materials fabrication processes.”

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Publication: Scientific Reports, (free download)

Issue/Year/DOI: Scientific Reports, Volume 1, Article number:121, (2011)
doi:10.1038/srep00121


Arbitrarily shaped high-coherence electron bunches from cold atoms

July, 2011

Author(s): A. J. McCulloch, D. V. Sheludko, S. D. Saliba, S. C. Bell, M. Junker, K. A. Nugent & R. E. Scholten

Abstract:

“Ultrafast electron diffractive imaging of nanoscale objects such as biological molecules and defects in solid-state devices provides crucial information on structure and dynamic processes: for example, determination of the form and function of membrane proteins, vital for many key goals in modern biological science, including rational drug design. High brightness and high coherence are required to achieve the necessary spatial and temporal resolution, but have been limited by the thermal nature of conventional electron sources and by divergence due to repulsive interactions between the electrons, known as the Coulomb explosion. It has been shown that, if the electrons are shaped into ellipsoidal bunches with uniform density, the Coulomb explosion can be reversed using conventional optics, to deliver the maximum possible brightness at the target. Here we demonstrate arbitrary and real-time control of the shape of cold electron bunches extracted from laser-cooled atoms. The ability to dynamically shape the electron source itself and to observe this shape in the propagated electron bunch provides a remarkable experimental demonstration of the intrinsically high spatial coherence of a cold-atom electron source, and the potential for alleviation of electron-source brightness limitations due to Coulomb explosion.”

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Publication: Nature Physics, (subscription required)

Issue/Year/DOI: Nature Physics, 7, 785–788, (2011)
doi:10.1038/nphys2052


Far field subwavelength focusing using optical eigenmodes

May, 2011

Author(s): Jörg Baumgartl, Sebastian Kosmeier, Michael Mazilu, Edward T. F. Rogers, Nikolay I. Zheludev, and Kishan Dholakia.

Abstract:

“We report the focusing of light to generate a subdiffractive, subwavelength focal spot of full width half maximum 222 nm at an operating wavelength of 633 nm using an optical eigenmode approach. Crucially, the spot is created in the focal plane of a microscope objective thus yielding a practical working distance for applications. The optical eigenmode approach is implemented using an optimal superposition of Bessel beams on a spatial light modulator. The effects of partial coherence are also discussed. This far field method is a key advance toward the generation of subdiffractive optical features for imaging and lithographic purposes.”

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Publication: Applied Physics Letters, (subscription required)

Issue/Year/DOI: Appl. Phys. Lett. 98, 181109 (2011)
doi:10.1063/1.3587636


A high speed wavefront determination method based on spatial frequency modulations for focusing light through random scattering media

February, 2011

Author(s): Meng Cui

Abstract:

“A large number of degrees of freedom are required to produce a high quality focus through random scattering media. Previous demonstrations based on spatial phase modulations suffer from either a slow speed or a small number of degrees of freedom. In this work, a high speed wavefront determination technique based on spatial frequency domain wavefront modulations is proposed and experimentally demonstrated, which is capable of providing both a high operation speed and a large number of degrees of freedom. The technique was employed to focus light through a strongly scattering medium and the entire wavefront was determined in 400 milliseconds, ~three orders of magnitude faster than the previous report.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 19, Issue 4, pp. 2989-2995 (2011)
doi:10.1364/OE.19.002989


Dynamic generation of Debye diffraction-limited multifocal arrays for direct laser printing nanofabrication

January, 2011

Author(s): Han Lin, Baohua Jia, and Min Gu

Abstract:

“We propose a Debye-theory-based iterative method to produce accurate phase patterns for generating highly uniform diffraction-limited multifocal arrays with a high-NA objective. It is shown that by using the Debye method, the uniformity of the diffraction-limited focal arrays can reach 99%, owing to the critical consideration of the depolarization effect associated with high-NA objectives. The generated phase patterns are implemented in fast dynamic laser printing nanofabrication for the generation of individually controlled high-quality microvoid arrays in a solid polymer material by a single exposure of a femtosecond laser beam. As a result of the high-quality multifocal arrays, functional three-dimensional photonic crystals possessing multiple stopgaps with suppression up to 80% in transmission spectra are demonstrated.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 3, pp. 406-408 (2011)
doi:10.1364/OL.36.000406


Frequency bandwidth of light focused through turbid media

January, 2011

Author(s): Frerik van Beijnum, Elbert G. van Putten, Ad Lagendijk, and Allard P. Mosk

Abstract:

“We study the effect of frequency detuning on light focused through turbid media. By shaping the wavefront of the incident beam light is focused through an opaque scattering layer. When detuning the laser we observe a gradual decrease of the focus intensity, while the position, size,and shape of the focus remain the same within experimental accuracy. The frequency dependence of the focus intensity follows a measured speckle correlation function. We support our experimental findings with calculations based on transport theory. Our results imply wavefront shaping methods can be generalized to allow focusing of optical pulses in turbid media.”

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Publication: Optics Letters, (subscription required)

Issue/Year/DOI: Optics Letters, Vol. 36, Issue 3, pp. 373-375 (2011)
doi:10.1364/OL.36.000373


Constructing petal modes from the coherent superposition of Laguerre-Gaussian modes

January, 2011

Author(s): Darryl Naidoo, Andrew Forbes, Kamel Ait-Ameur, Marc Brunel

Abstract:

“An experimental approach in generating Petal-like transverse modes, which are similar to what is seen in porro-prism resonators, has been successfully demonstrated. We hypothesize that the petal-like structures are generated from a coherent superposition of Laguerre-Gaussian modes of zero radial order and opposite azimuthal order. To verify this hypothesis, visually based comparisons such as petal peak to peak diameter and the angle between adjacent petals are drawn between experimental data and simulated data. The beam quality factor of the Petal-like transverse modes and an inner product interaction is also experimentally compared to numerical results.”

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Publication: SPIE Proceedings, (subscription required)

Issue/Year/DOI: Proc. SPIE 7913, 791304 (2011)
doi:10.1117/12.876854