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


Parallel phase-shifting digital holography with adaptive function using phase-mode spatial light modulator

May, 2012

Author(s): Miao Lin, Kouichi Nitta, Osamu Matoba, and Yasuhiro Awatsuji

Abstract:

“Parallel phase-shifting digital holography using a phase-mode spatial light modulator (SLM) is proposed. The phase-mode SLM implements spatial distribution of phase retardation required in the parallel phase-shifting digital holography. This SLM can also compensate dynamically the phase distortion caused by optical elements such as beam splitters, lenses, and air fluctuation. Experimental demonstration using a static object is presented.”

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Publication: Applied Optics, (subscription required)

Issue/Year/DOI: Applied Optics, Vol. 51, Issue 14, pp. 2633-2637 (2012)
doi:10.1364/AO.51.002633


An active coronagraph using a liquid crystal array for exoplanet imaging: principle and testing

May, 2012

Author(s): Xi Zhang, De-Qing Ren, Yong-Tian Zhu and Jiang-Pei Dou.

Abstract:

“High-contrast imaging coronagraphs, used for the detection of exoplanets, have always adopted passive coronagraph optical components. It is therefore impossible to actively optimize the coronagraphs to achieve their best performance. To solve this problem, we propose a novel high-contrast imaging coronagraph which combines a liquid crystal array (LCA) for active pupil apodization and a deformable mirror (DM) for phase correction. The LCA we use is an amplitude-only spatial light modulator. The LCA is well calibrated and compensates for its amplitude non-uniformity and nonlinear intensity responsivity. We measured the imaging contrasts of the coronagraph system with the LCA only and without the DM deployed. Imaging contrasts of 10-4 and 10-5 can be reached at an inner working angular distance of 2.5 and 5λ/D, respectively. A simulation shows that the phase errors on the coronagraph pupil limit the contrast performance. The contrast could be further improved if a DM is deployed to correct the phase errors induced by the LCA and coronagraph optics.”

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Publication: Research in Astronomy and Astrophysics, (subscription required)

Issue/Year/DOI: Res. Astron. Astrophys., Vol. 12, Issue 5,(2012)
doi:10.1088/1674-4527/12/5/011


Double peacock eye optical element for extended focal depth imaging with ophthalmic applications

April, 2012

Author(s): Lenny A. Romero, María S. Millán, Zbigniew Jaroszewicz, Andrzej Kolodziejczyk.

Abstract:

“The aged human eye is commonly affected by presbyopia, and therefore, it gradually loses its capability to form images of objects placed at different distances. Extended depth of focus (EDOF) imaging elements can overcome this inability, despite the introduction of a certain amount of aberration. This paper evaluates the EDOF imaging performance of the so-called peacock eye phase diffractive element, which focuses an incident plane wave into a segment of the optical axis and explores the element’s potential use for ophthalmic presbyopia compensation optics. Two designs of the element are analyzed: the single peacock eye, which produces one focal segment along the axis, and the double peacock eye, which is a spatially multiplexed element that produces two focal segments with partial overlapping along the axis. The performances of the peacock eye elements are compared with those of multifocal lenses through numerical simulations as well as optical experiments in the image space. The results demonstrate that the peacock eye elements form sharper images along the focal segment than the multifocal lenses and, therefore, are more suitable for presbyopia compensation. The extreme points of the depth of field in the object space, which represent the remote and the near object points, have been experimentally obtained for both the single and the double peacock eye optical elements. The double peacock eye element has better imaging quality for relatively short and intermediate distances than the single peacock eye, whereas the latter seems better for far distance vision.”

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Publication: Journal of Biomedical Optics , (subscription required)

Issue/Year/DOI: J. Biomed. Opt. 17, 046013 (Apr 27, 2012)
doi:10.1117/1.JBO.17.4.046013


Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination

March, 2012

Author(s): Antonio Ambrosio, Lorenzo Marrucci, Fabio Borbone, Antonio Roviello, Pasqualino Maddalena

Abstract:

“When an azobenzene-containing polymer film is exposed to a non-uniform illumination, a light-induced mass migration process may be induced, leading to the formation of relief patterns on the polymer free surface. Despite a research effort of many years and several proposed models many aspects of this phenomenon remain not well understood. Here we report the appearance of spiral-shaped relief patterns on the polymer under the illumination of focused Laguerre-Gauss beams, having helical wavefront and an optical vortex at their axis. The induced spiral reliefs are sensitive to the vortex topological charge and to the wavefront handedness. These findings are unexpected, because the “doughnut”-shaped intensity profile of Laguerre- Gauss beams contains no information about the wavefront handedness. We propose a model that explains the main features of this phenomenon from the surface-mediated interference of the longitudinal and the transverse components of the optical field. These results may find applications in optical micro- and nanolithography and optical-field. ”

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Publication: eprint arXiv:1203.5205, (free download)

Issue/Year/DOI: eprint arXiv:1203.5205 (2012)
Bibliographic Code: 2012arXiv1203.5205A


Determination of wavefront structure for a Hartmann Wavefront Sensor using a phase-retrieval method

March, 2012

Author(s): A. Polo, V. Kutchoukov, F. Bociort, S.F. Pereira, and H.P. Urbach

Abstract:

“We apply a phase retrieval algorithm to the intensity pattern of a Hartmann wavefront sensor to measure with enhanced accuracy the phase structure of a Hartmann hole array. It is shown that the rms wavefront error achieved by phase reconstruction is one order of magnitude smaller than the one obtained from a typical centroid algorithm. Experimental results are consistent with a phase measurement performed independently using a Shack-Hartmann wavefront sensor.”

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Publication: Optics Express, (free download)

Issue/Year/DOI: Optics Express, Vol. 20, Issue 7, pp. 7822-7832 (2012)
doi:10.1364/OE.20.007822


Three dimensional optical twisters-driven helically stacked multi-layered microrotors

March, 2012

Author(s): Jolly Xavier, Raktim Dasgupta, Sunita Ahlawat, Joby Joseph, and Pradeep Kumar Gupta

Abstract:

“We demonstrate tunable helically stacked multi-layered microrotors realized in vortex-embedded three dimensional (3D) optical twister patterns. Intensity-tunable annular irradiance profiles with higher order vortex are generated as well as simultaneously unfolded by phase-engineered multiple plane wave interference. In the individually tunable 3D helical bright arms of these unfolded vortex structures, 2 μm silica beads are optically trapped as spiraling multilayered handles of multi-armed microrotors. Further, multiple rows of such microrotors are parallelly actuated with controllable sense of rotation. We also present our observation on helical 3D stacking of micro-particles in these longitudinally gyrating multi-armed rotor traps.”

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Publication: Applied Physics Letters, (subscription required)

Issue/Year/DOI: Applied Physics Letters, Volume 100, Issue 12, (2012)
doi:10.1063/1.3693413


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


Experimental generation and characterization of Devil’s vortex-lenses

February, 2012

Author(s): A. Calatayud, J. A. Rodrigo, L. Remón, W. D. Furlan, G. Cristóbal und J. A. Monsoriu

Abstract:

“We propose the first experimental approach for both generation and characterization of high quality Devil’s vortex-lenses. These new type of lenses, able to produce a sequence of optical vortices, are addressed onto a programmable spatial light modulator (SLM) operating in phase-only modulation. The static aberrations arising by the lack of flatness of the SLM display are characterized and mostly compensated by using a Shack–Hartmann wavefront sensor. The analysis of the residual aberrations and their effect on the vortex-lens performance are studied. ”

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Publication: Applied Physics B: Lasers and Optics, (subscription required)

Issue/Year/DOI: Applied Physics B, Volume 106, Number 4 (2012), 915-919,
doi:10.1007/s00340-012-4913-0


Vertical differential interference contrast

February, 2012

Author(s): Michael Warber, Tobias Haist, Malte Hasler, and Wolfgang Osten

Abstract:

“We propose a new phase contrast filtering technique based on a combination of a focused and a defocused point-spread-function. This way, an axial shear is introduced in the imaging system. Compared to conventional differential interference contrast, an isotropic behavior is achieved. The lateral resolution is improved compared to conventional defocusing. Furthermore, the digital combination of multiple images leads to strongly enhanced visualization of small structures. We show simulated results as well as experimental results using a spatial-light modulator-based microscope.”

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Publication: Optical Engineering, (subscription required)

Issue/Year/DOI: Opt. Eng., Volume 51, Issue 1, 013204, (2012)
doi:10.1117/1.OE.51.1.013204