On the resilience of scalar and vector vortex modes in turbulence

Author(s):

Cox, Mitchell A.; Rosales-Guzman, Carmelo; Lavery, Martin P. J.; Versfeld, Daniel J. & Forbes, Andrew

Abstract:

“Free-space optical communication with spatial modes of light has become topical due to the possibility of dramatically increasing communication bandwidth via Mode Division Multiplexing (MDM). While both scalar and vector vortex modes have been used as transmission bases, it has been suggested that the latter is more robust in turbulence. Using orbital angular momentum as an example, we demonstrate theoretically and experimentally that the crosstalk due to turbulence is the same in the scalar and vector basis sets of such modes. This work brings new insights about the behaviour of vector and scalar modes in turbulence, but more importantly it demonstrates that when considering optimal modes for MDM, the choice should not necessarily be based on their vectorial nature.”

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Publication: Opt. Express
Issue/Year: Opt. Express, Volume 24; Number 16; Pages 18105-18113; 2016
DOI: 10.1364/OE.24.018105

Focusing light into desired patterns through turbid media by feedback-based wavefront shaping

Author(s):

Lipeng Wan and Ziyang Chen and Huiling Huang and Jixiong Pu

Abstract:

“We demonstrate that the focusing of light into desired patterns through turbid media can be realized using feedback-based wavefront shaping. Three desired focused patterns—a triangle, a circle, and a rectangle—are used as examples to study this ability. During the process of modulating scattered light, the Pearson’s correlation coefficient is introduced as a feedback signal. It is found that the speckle field formed by the turbid media gradually transforms into the desired pattern through a process of modulation of the input beam wave front. The proposed approach has potential applications in biomedical treatment and laser material processing.”

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Publication: Applied Physics B
Issue/Year: Applied Physics, B 122, 204 (2016)
DOI: 10.1007/s00340-016-6466-0

Pre-turbulence compensation of orbital angular momentum beams based on a probe and the Gerchberg–Saxton algorithm

Author(s):

Fu, Shiyao; Zhang, Shikun; Wang, Tonglu & Gao, Chunqing

Abstract:

“We propose a scheme that uses a probe Gaussian beam and the Gerchberg-Saxton (GS) algorithm to realize the pre-turbulence compensation of beams carrying orbital angular momentum (OAM). In the experiment, spatial light modulators are utilized to simulate the turbulent atmosphere and upload the retrieval holograms. A probe Gaussian beam is used to detect the turbulence. Then, the retrieval holograms, which can correct the phase distortion of the OAM beams, are obtained by the GS algorithm. The experimental results show that single or multiplexed OAM beams can be compensated well. The compensation performances under different iterations are also analyzed.”

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Publication: Opt. Lett.
Issue/Year: Opt. Lett., Volume 41; Number 14; Pages 3185-3188; 2016
DOI: 10.1364/OL.41.003185

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

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

Binocular adaptive optics vision analyzer with full control over the complex pupil functions

Author(s): Christina Schwarz, Pedro M. Prieto, Enrique J. Fernández, and Pablo Artal

Abstract:

“We present a binocular adaptive optics vision analyzer fully capable of controlling both amplitude and phase of the two complex pupil functions in each eye of the subject. A special feature of the instrument is its comparatively simple setup. A single reflective liquid crystal on silicon spatial light modulator working in pure phase modulation generates the phase profiles for both pupils simultaneously. In addition, another liquid crystal spatial light modulator working in transmission operates in pure intensity modulation to produce a large variety of pupil masks for each eye. Subjects perform visual tasks through any predefined variations of the complex pupil function for both eyes. As an example of the system efficiency, we recorded images of the stimuli through the system as they were projected at the subject’s retina. This instrument proves to be extremely versatile for designing and testing novel ophthalmic elements and simulating visual outcomes, as well as for further research of binocular vision.”

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Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 36, Issue 24, pp. 4779-4781 (2011)
DOI: 10.1364/OL.36.004779

Coaxial holographic encoding based on pure phase modulation

Author(s): Wei Jia, Zhongyu Chen, Fung Jacky Wen, Changhe Zhou, Yuk Tak Chow, and Po Sheun Chung

Abstract:

“We describe a simple technique for coaxial holographic image recording and reconstruction, employing a spatial light modulator (SLM) modified in pure phase mode. In the image encoding system, both the reference beam in the outside part and the signal beam in the inside part are displayed by an SLM based on the twisted nematic LCD. For a binary image, the part with amplitude of “1” is modulated with random phase, while the part with amplitude of “0” is modulated with constant phase. After blocking the dc component of the spatial frequencies, a Fourier transform (FT) hologram is recorded with a uniform intensity distribution. The amplitude image is reconstructed by illuminating the reference beam onto the hologram, which is much simpler than existing phase modulated FT holography techniques. The technique of coaxial holographic image encoding and recovering with pure phase modulation is demonstrated theoretically and experimentally in this paper. As the holograms are recorded without the high-intensity dc component, the storage density with volume medium may be increased with the increase of dynamic range. Such a simple modulation method will have potential applications in areas such as holographic encryption and high-density disk storage systems.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 50, Issue 34, pp. H10-H15 (2011)
DOI: 10.1364/AO.50.000H10

Quantum control of electron spins in the two-dimensional electron gas of a CdTe quantum well with a pair of Raman-resonant phase-locked laser pulses

Author(s): Timothy M. Sweeney, Carey Phelps, and Hailin Wang

Abstract:

“We demonstrated optical spin control of a two-dimensional electron gas in a modulation-doped CdTe quantum well by driving a spin-flip Raman transition with a pair of phase-locked laser pulses. In contrast to single-pulse optical spin control, which features a fixed spin-rotation axis, manipulation of the initial relative phase of the pulse pair enables us to control the axis of the optical spin rotation. We show that the Raman pulse pair acts like an effective microwave field, mapping the relative optical phase onto the phase of the electron spin polarization and making possible ultrafast, all-optical, and full quantum control of the electron spins.”

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Publication: Physical Review B
Issue/Year: Phys. Rev. B, Volume 84, Issue 7, (2011)
DOI: 10.1103/PhysRevB.84.075321

Generation of Optical Vortices by Linear Phase Ramps

Author(s): Sunil Vyas

Abstract:

“Generation of optical vortices using linear phase ramps is experimentally demonstrated. When two regions of a wavefront have opposite phase gradients then along the line of phase discontinuity vortices can be generated. It is shown that vortices can evolve during propagation even with the unequal magnitude of tilt in the two regions of the wavefront. The number of vortices and their location depend upon the magnitude of tilt. vortex generation is experimentally realized by encoding phase mask on spatial light modulator and their presence is detected interferometrically. Numerical simulation has been performed to calculate the diffracted intensity distribution from the phase mask, and presence of vortices in the diffracted field is detected by computational techniques.”

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Publication: International Journal of Optics
Issue/Year: International Journal of Optics, Volume 2012, Article ID 794259, 6 pages, (2012)
DOI: 10.1155/2012/794259

Mean focal length of an aberrated lens

Author(s): Cosmas Mafusire and Andrew Forbes

Abstract:

“We outline an approach for the calculation of the mean focal length of an aberrated lens and provide closed-form solutions that show that the focal length of the lens is dependent on the presence of defocus, x-astigmatism, and spherical aberration. The results are applicable to Gaussian beams in the presence of arbitrary-sized apertures. The theoretical results are confirmed experimentally, showing excellent agreement. As the final results are in algebraic form, the theory may readily be applied in the laboratory if the aberration coefficients of the lens are known.”

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Publication: Journal of the Optical Society of America A
Issue/Year: JOSA A, Vol. 28, Issue 7, pp. 1403-1409 (2011)
DOI: 10.1364/JOSAA.28.001403

Phase extraction in microscopy using tunable defocusing by means of a SLM

Author(s): Luis Camacho, Vicente Micó, Javier García, Zeev Zalevsky

Abstract:

“In many practical microscopy applications the use of phase information is crucial. In this contribution we propose a method for phase extraction in a microscopy system based on analysis of images with varying defocusing. The system has no mobile parts owing to the defocusing by means of a spatial light modulator. The base of the method is the captre of images in a microscope with varying tube lens focal lengths. This produce a set of intensity images, all of them related, because the can be generated by free space propagation of a complex distribution which is unknown.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE 8082, 80820O (2011);
DOI: 10.1117/12.889591