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ABSTRACT: We propose and experimentally demonstrate a new method for free-space optical (FSO) communication, where the transmitter encodes data into a composite computer-generated hologram and the receiver decodes through a retrieved array of sidelobe-modulated optical vortices (SMOVs). By employing the SMOV generation and detection technique, the usual stringent alignment and phase-matching requirement of the detection of optical vortices is released. In transmitting a gray-scale picture with 180×180 pixels, a bit error rate as low as 3.01×10<sup>-3</sup> has been achieved. Due to the orbital angular momentum multiplexing and spatial paralleling, this FSO communication method possesses the ability to greatly increase the capacity of data transmission.
Optics Letters 02/2013; 38(4):588-90. · 3.40 Impact Factor
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ABSTRACT: Plasmonic vortices (PVs) are generated by focusing a radially polarized optical vortex (OV) beam onto a metal surface. The intensity distribution of the PV is registered with a near-field scanning optical microscopy and agrees well with a theoretical prediction as well as numerical calculation. Beside the dark central spot, the numerical calculation also shows an azimuthal Poynting vector belonging to the PV, implying that the orbital angular momentum (OAM) was transferred from the radially polarized OV. To directly verify the OAM, plasmonic trapping experiments with gold micrometer particles are performed and the particle rotation is visualized. Further experiments by varying the topological charge of radially polarized OVs show the corresponding changes in rotation in terms of speed and radius.
Optics Letters 11/2012; 37(22):4627-9. · 3.40 Impact Factor
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ABSTRACT: An improved sinusoidal phase plate is proposed by adding a new parameter to the conventional sinusoidal phase plate. A series of performance comparisons are made among various phase plates, including sinusoidal, cubic phase, and the modified logarithmic phase. The results demonstrate that the improved sinusoidal phase plate can further extend the depth of field in incoherent hybrid imaging systems, with lower surface relief phase structures fabricated in photoresist (AR-N 4340, ALL Resist, Germany).
Optics Letters 11/2012; 37(21):4534-6. · 3.40 Impact Factor
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ABSTRACT: Novel hybrid-polarized vector beams with radial and azimuthal polarization states in arbitrary fan-sectors are generated and studied for manipulating surface plasmon polaritons (SPPs). The method has high energy conversion efficiency based on an interferometric arrangement with a Dammann vortex phase grating. The polarization states of generated beams are measured by a linear polarizer and show excellent agreement with theoretical predictions. The manipulation properties of the hybrid-polarized beams on SPPs excitation and distribution are demonstrated by both experiments and simulations. The results show that focusing or standing wave patterns of SPPs can be obtained depending on the polarization of the beams.
Optics Express 10/2012; 20(22):24748-53. · 3.59 Impact Factor
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ABSTRACT: A novel phase modulation method for dynamic manipulation of surface plasmon polaritons (SPPs) with a phase engineered optical vortex (OV) beam illuminating on nanoslits is experimentally demonstrated. Because of the unique helical phase carried by an OV beam, dynamic control of SPP multiple focusing and standing wave generation is realized by changing the OV beam's topological charge constituent with the help of a liquid-crystal spatial light modulator. Measurement of SPP distributions with near-field scanning optical microscopy showed an excellent agreement with numerical predictions. The proposed phase modulation technique for manipulating SPPs features has seemingly dynamic and reconfigurable advantages, with profound potential for development of SPP coupling, routing, multiplexing and high-resolution imaging devices on plasmonic chips.
Nanotechnology 09/2012; 23(38):385204. · 3.98 Impact Factor
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ABSTRACT: We generate and investigate a self-healing pillar array with a specific phase function comprised of four engineered cubic phase plates with encoded amplitude and phase. This array shows an enhanced self-healing effect at arbitrary obstructed positions in transverse as well as longitudinal locations along propagation where its symmetrical pattern with uniform intensity distribution can be maintained. The transverse power flow in terms of Poynting vector is studied for better interpretation of the self-healing property.
Optics Letters 09/2012; 37(17):3540-2. · 3.40 Impact Factor
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ABSTRACT: To quantify OCT images of rectal tissue for clinic diagnosis, the scattering coefficient of the tissue is extracted by curve fitting the OCT signals to a confocal single model. A total of 1000 measurements (half and half of normal and malignant tissues) were obtained from 16 recta. The normal rectal tissue has a larger scattering coefficient ranging from 1.09 to 5.41 mm⁻¹ with a mean value of 2.29 mm⁻¹ (std:±0.32), while the malignant group shows lower scattering property and the values ranging from 0.25 to 2.69 mm⁻¹ with a mean value of 1.41 mm⁻¹ (std:±0.18). The peri-cancer of recta has also been investigated to distinguish the difference between normal and malignant rectal tissue. The results demonstrate that the quantitative analysis of the rectal tissue can be used as a promising diagnostic criterion of early rectal cancer, which has great value for clinical medical applications.
Physics in Medicine and Biology 07/2012; 57(16):5235-44. · 2.83 Impact Factor
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ABSTRACT: A novel phase-sensitive surface plasmon resonance (pSPR) biosensor based on differential phase measurement between two cylindrical vector beams, namely radially polarized and azmuthally polarized beams, is proposed and studied in an inverted microscope. Different from a fixed angle or a relatively small angular range for SPR excitation in the attenuated total reflection (ATR) configuration, the signal beam focused by a total internal reflection fluorescence microscopic objective contains the entire angular range from 0 to the maximum angle given by the numerical aperture, leading to a dynamic range of 0.41 RIU which is over seven times wider than the best result of the ATR pSPR sensor. Moreover, with the technique of differential phase measurement between radial and azimuthal polarizations employed in our configuration, high sensitivity of ±9.05×10(-8) refractive index unit/1 deg can simultaneously be achieved in principle. The proposed technique maintains the unique advantages in terms of securing high imaging resolution and sensitivity with an ultra-wide dynamic range simultaneously.
Optics Letters 06/2012; 37(11):2091-3. · 3.40 Impact Factor
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ABSTRACT: In this paper we report on recent development in the areas of optical vortices generated by micro-optical elements and applications
of optical vortices, including optical manipulation, radial polarization and secure free space optical communication
Optoelectronics Letters 04/2012; 3(2):136-140.
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ABSTRACT: Plasmonic vortices (PV) excited by a highly focused radially polarized
optical vortex (RPOV) beam on a metal surface are investigated experimentally
and theoretically. The proposed method reveals a direct phase singularity and
orbital angular momentum (OAM) transfer from an incident structured beam to its
counterpart in surface plasmon with dynamic, reconfigurable and high-efficiency
advantages. The plasmonic field pattern, phase distributions, Poynting vector
and focusing efficiency of PV are studied in detail. Experimental verification
further shows that nanoparticles can be confined and manipulated within the
region of PV and orbital rotation speed of the trapped particles is altered
dynamically by changing the topological charge of the incident light.
10/2011;
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ABSTRACT: We experimentally demonstrate that a Bessel-like amplitude modulated spiral phase filter can be used in a real-time spatial image edge enhancement system in optical microscopy for biological sample imaging. Compared with previous methods based on a conventional spiral phase filter, a dark-field spiral phase filter and the Laguerre–Gaussian modulated spiral phase filter, the proposed technique further reduces the imaging diffraction noise. Experimental verifications in edge enhancement are implemented by a phase-only spatial light modulator for realizing the amplitude modulated spiral phase. It is shown that the proposed technique is able to efficiently suppress the diffraction noise and achieve high quality edge enhancement images for biological samples.
Journal of optics 09/2011; 13(10):105704. · 1.57 Impact Factor
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ABSTRACT: Generation of a nondiffracting transversally polarized beam by means of transmitting an azimuthally polarized beam through a multibelt spiral phase hologram and then highly focusing by a high-NA lens is presented. A relatively long depth of focus (∼4.84λ) of the electric field with only radial and azimuthal components is achieved. The polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the polarization is spatially varying and entirely transversally polarized, and the polarization singularity disappears at the beam center, which makes the central bright channel possible.
Optics Letters 09/2011; 36(17):3479-81. · 3.40 Impact Factor
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ABSTRACT: We demonstrate an experimental result that shows the phase singularity of surface plasmon waves generated by the direct transform of optical vortices at normal incidence focused on a structureless metal surface. The near-field two-dimensional intensity distribution near the focal plane is experimentally examined by using near-field scanning optical microscopy and shows a good agreement with the finite-difference time-domain simulation result. The experimental realization demonstrates a potential of the proposed excitation scheme to be reconfigured locally with advantages over structures milled into optically thick metallic films for plasmonics applications involving plasmonic vortices.
Optics Letters 08/2011; 36(16):3287-9. · 3.40 Impact Factor
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ABSTRACT: We propose an approach to the generation of nondiffracting quasi-circularly polarized beams by a highly focusing azimuthally polarized beam using an amplitude modulated spiral phase hologram. Numerical verifications are implemented in the calculation of the electromagnetic fields and Poynting vector field near the focus based on the vector diffraction theory, and the polarization of the wavefront near the focal plane is analyzed in detail by calculating the Stokes polarization parameters. It is found that the electric field, magnetic field, and Poynting vector field can simultaneously be uniform and nondiverging over a relatively long axial range of ~7.23λ. In the transverse plane, the ellipticity and azimuthal angle of the local polarization ellipse varies from point to point. No polarization singularity and phase singularity are found at the beam center, which makes the bright spot possible.
Journal of the Optical Society of America A 08/2011; 28(8):1716-20. · 1.56 Impact Factor
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ABSTRACT: A dynamic optical tweezers system is employed for generation of an optical trap in continuous rotation for manipulating a biological cell in an aqueous solution. When the rotating speed is increased, the trapped cell experiences an augmented viscous drag force, and eventually it escapes from the trap at the critical rotating speed: when the drag force is greater than the trapping force. With experimental verifications, the method can easily be employed to differentiate cells in terms of trapping forces due to different refractive indices. The proposed method is a simple, robust, accurate and noninvasive label-free technique for cell detection.
The Review of scientific instruments 06/2011; 82(6):064301. · 1.52 Impact Factor
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ABSTRACT: We present an approach to calculating the complex amplitude of a three-dimensional (3D) diffracted light field in the paraxial approximation based on a 3D Fourier transform. Starting from the Huygens-Fresnel principle, the method is first developed for the computation of the light distribution around the focus of an apertured spherical wave. The method, with modification, is then extended to treat the 3D diffraction of an aperture with an arbitrary transmittance function.
Optics Letters 04/2011; 36(8):1341-3. · 3.40 Impact Factor
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ABSTRACT: Manipulation of surface plasmon polaritons (SPP) by phase modulation of incident light beams is proposed with analytical and numerical verifications when an optical vortex (OV) beam is employed as an example. Fundamental functionalities of a plasmonic chip such as in-plane focusing, coupling and multiplexing of SPP by sequentially varying the topological charge of OV beam are demonstrated. Complementary to the manually-controlled optical-path-different technique reported in literature, the proposed method reveals a direct phase transform from OV beam to SPP with dynamic and reconfigurable advantages.
Optics Express 01/2011; 19(1):224-9. · 3.59 Impact Factor
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ABSTRACT: In optical coherence tomography (OCT) systems, there is a trade-off between the depth of focus (DOF) and lateral resolution when conventional lenses are used. We propose a new method that employs a modified fractal generalized zone plate (MFraGZP) combined with a conventional lens to improve the trade-off effect, with an extended DOF of about 2.5 mm (14 times larger) while the lateral resolution is maintained at similar to 9.5 mu m. As an example, images of the calibration microspheres are obtained and demonstrated with the extended DOF in a spectral domain OCT system.
Journal of Optics. 01/2011; 13(5).
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ABSTRACT: We report an approach to the increase of signal channels in free-space optical communication based on composed optical vortices (OVs). In the encoding process, conventional algorithm employed for the generation of collinearly superimposed OVs is combined with a genetic algorithm to achieve high-volume OV multiplexing. At the receiver end, a novel Dammann vortex grating is used to analyze the multihelix beams with a large number of OVs. We experimentally demonstrate a digitized system which is capable of transmitting and receiving 16 OV channels simultaneously. This system is expected to be compatible with a high-speed OV multiplexing technique, with potentials to extremely high-volume information density in OV communication.
Optics Express 01/2011; 19(2):482-92. · 3.59 Impact Factor
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ABSTRACT: An on-chip optical trapping and sorting system composed of a microchamber and a microlens array (MLA) is demonstrated. The MLA focuses the incident light into multiple confocal spots to trap the particles within the microchamber. The SiO(2)/ZrO(2) solgel material is introduced in the fabrication of MLA for its unique optical and chemical characters. Moreover, in order to prove the effectiveness of the system, experimental demonstration of multibeam trapping and locked-in transport of micropolymer particles in the microchamber is implemented. The system may easily be integrated as microfluidic devices, offering a simple and efficient solution for optical trapping and sorting of biological particles in lab-on-a-chip technologies.
Applied Optics 01/2011; 50(3):318-22. · 1.41 Impact Factor
