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ABSTRACT: A hybrid spiral plasmonic lens that consists of alternating spiral slot and spiral triangular sub-aperture array can differentiate circular polarization of different handedness and enable a miniature circular polarization analyzer design with high efficiency. The improved performance compared to pure spiral slot lens comes from the fact that the hybrid lens is capable of focusing both the radial and the azimuthal polarization components of a circular polarization, doubling the coupling efficiency. In this paper, the spin-dependent plasmonic focusing properties of a spatially arranged triangular sub-aperture array and a hybrid spiral plasmonic lens are demonstrated using a collection mode near field scanning optical microscope. The coupling efficiency could be further improved through optimizing the geometry of the hybrid lens.
Optics Express 11/2012; 20(24):26299-307. · 3.59 Impact Factor
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ABSTRACT: We analytically and numerically study the emission properties of an electric dipole coupled to a plasmonic spiral structure with different pitch. As a transmitting antenna, the spiral structure couples the radiation from the electric dipole into circularly polarized emitted photons in the far field. The spin carried by the emitted photons is determined by the handedness of the spiral antenna. By increasing the spiral pitch in the unit of surface plasmon wavelength, these circularly polarized photons also gain orbital angular momentum with different topological charges. This phenomenon is attributed to the presence of a geometric phase arising from the interaction of light from point source with the anisotropic spiral structure. The circularly polarized vortex emission from such optically coupled spiral antenna also has high directivity, which may find important applications in quantum optical information, single molecule sensing, and integrated photonic circuits.
Optics Express 08/2012; 20(17):18819-26. · 3.59 Impact Factor
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ABSTRACT: Coupling nanoscale emitters via optical antennas enables comprehensive control of photon emission in terms of intensity, directivity and polarization. In this work we report highly directional emission of circularly polarized photons from quantum dots coupled to a spiral optical antenna. The structural chirality of the spiral antenna imprints spin state to the emitted photons. Experimental results reveal that a circular polarization extinction ratio of 10 is obtainable. Furthermore, increasing the number of turns of the spiral gives rise to higher antenna gain and directivity, leading to higher field intensity and narrower angular width of emission pattern in the far field. For a five-turn Archimedes' spiral antenna, field intensity increase up to 70-fold simultaneously with antenna directivity of 11.7 dB has been measured in the experiment. The highly directional circularly polarized photon emission from such optically coupled spiral antenna may find important applications in single molecule sensing, quantum optics information processing and integrated photonic circuits as a nanoscale spin photon source.
Optics Express 08/2012; 20(17):19297-304. · 3.59 Impact Factor
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ABSTRACT: The spin dependence of the focusing behavior of a spiral slot plasmonic lens can be utilized for a miniature circular polarization analyzer. However, the azimuthal polarization component of the incident circular polarization does not contribute to surface plasmon excitation and focusing because it is TE polarized with respect to the spiral slot. In this Letter, a hybrid metallic lens that consists of alternating spiral triangle array and spiral slot is designed to improve the plasmonic coupling efficiency. The spiral triangle array is responsible for coupling the azimuthal polarization component into surface plasmon. Numerical studies show that the field enhancement at the focus and power conversion efficiency can be increased by 39.53% and 94.69% compared to that of pure spiral slot plasmonic lens.
Optics Letters 05/2012; 37(9):1442-4. · 3.40 Impact Factor
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ABSTRACT: A single notch plasmonic spectral filter design using evanescently coupled resonant ultrathin metal grating is numerically
studied in this article. Due to excitation and coupling of long range surface plasmon between the metal grating nanowires,
a deep and narrow reflection spectrum dip can be obtained. Narrower spectral bandwidth is achieved through decreased damping
from the existence of large dielectric gaps between the grating nanowires. This physical explanation is confirmed by the field
distribution calculation. As an example, a single notch filter design with full width half maximum band width less than 3nm
centered at 808nm is presented.
Plasmonics 04/2012; 3(2):103-108. · 2.99 Impact Factor
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ABSTRACT: Owing to a geometric phase effect, an isosceles triangular aperture etched into thin metal film leads to constructive or destructive interference of surface plasmons excited at the two equal sides under linearly polarized illumination. Through appropriate spatial arrangement of an array of triangles, a highly confined focal spot beyond the diffraction limit can be achieved at the geometric center under azimuthally polarized excitation with field enhancement comparable to a bull's eye plasmonic lens under radially polarized illumination. Through simply rotating the orientation of each triangle aperture by 90°, the plasmonic structure defocuses the same azimuthal polarization illumination due to destructive interference caused by a geometric π-phase difference between the two sides of the triangle and between the adjacent triangles.
Optics Letters 02/2012; 37(4):581-3. · 3.40 Impact Factor
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ABSTRACT: In this Letter, we study the emission properties of an electric dipole emitter coupled to a plasmonic spiral structure. The plasmonic spiral structure functions as an optical antenna, coupling the electric dipole emission into circularly polarized unidirectional emission in the far field. Increasing number of turns of the spiral leads to narrower angular width of the emission pattern in the far field. For a spiral antenna with six turns, antenna directivity of 23.5 dB with a directional emission into a narrow angular cone of 4.3° can be achieved. The emitted photons carry spin that is essentially determined by the handedness of the spiral antenna. By reversing the spiral, one can switch the polarization of the emission field between left-hand and right-hand circular polarizations. The spiral antenna may be used as a nanoscale circular polarization source in single molecule sensing, single-photo sources, and integrated photonic circuits.
Optics Letters 12/2011; 36(23):4533-5. · 3.40 Impact Factor
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ABSTRACT: We report the generation of cylindrical vector beams using a concentric metallic grating fabricated on optical fibers with a period smaller than the wavelength of the incident light. Similar to the wiregrid linear polarizer, such a subwavelength metallic annular structure strongly reflects azimuthal polarization and allows radial polarization to transmit through. Due to the polarization selectivity of the concentric metallic grating, a cylindrical vector beam is obtained when a circularly polarized light is launched into the fiber. Such a device is suitable for the end mirror coupler in an all-fiber laser design to produce radially polarized modes.
Journal of optics 11/2010; 13(1):015003. · 1.57 Impact Factor
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ABSTRACT: A spiral plasmonic lens can focus circular polarization of a given handedness while simultaneously defocus the circular polarization of the opposite chirality, which may be used as a miniature circular polarization analyzer. In this letter, we experimentally investigated the plasmonic focusing properties of the spiral lens using a collection mode near-field scanning optical microscope. A single Archimedes' spiral slot with a single turn was etched through gold thin film as a spiral plasmonic lens. The plasmonic field at the focus of a spiral lens strongly depends on the spin of the incident photon. Circular polarization extinction ratio better than 50 is obtainable with a device size as small as only 4 times of surface plasmon wavelength.
Nano Letters 06/2010; 10(6):2075-9. · 13.20 Impact Factor
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ABSTRACT: The spiral plasmonic lens is capable of focusing the left-hand and right-hand circular polarizations into spatially separated plasmonic fields caused by the geometric phase effect. Its function as a circular polarization analyzer has been studied analytically and numerically in a previous Letter [Opt. Lett.34, 3047 (2009)OPLEDP0146-959210.1364/OL.34.003047]. Single Archimedes' spiral grooves with lateral sizes of approximately 4lambda(spp) (approximately 2.8 microm) were milled into a gold thin film by using a focused ion beam. The function of such a simple spiral plasmonic lens serving as a circular polarization analyzer was experimentally characterized with two-photon fluorescence microscopy. The circular polarization extinction ratio of the two-photon fluorescent signal is estimated to be larger than 200 for a detector diameter up to 0.3lambda(spp).
Optics Letters 06/2010; 35(11):1755-7. · 3.40 Impact Factor
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ABSTRACT: A simple spiral plasmonic lens is studied both analytically and numerically. Owing to the geometric phase effect, a spiral plasmonic lens focuses the left-hand and right-hand circular polarizations into spatially separated plasmonic fields. Such a spatial multiplexing of the field distribution is utilized in miniature circular polarization analyzer design. A circular polarization extinction ratio better than 100 is obtainable with a device size as small as 4lambda(spp). The spiral plasmonic lens provides efficient plasmonic focusing while it eliminates the requirement of centering the incident beam to the plasmonic lens, making it suitable for full Stokes parameter polarimetric imaging applications.
Optics Letters 10/2009; 34(20):3047-9. · 3.40 Impact Factor
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ABSTRACT: Optimal plasmonic focusing can be achieved through matching the rotational symmetry of the plasmonic lens to the polarization symmetry of a radially polarized illumination. In this letter, we report the experimental confirmation of the focusing properties and field enhancement effect of plasmonic lens made of multiple concentric annular rings using a collection mode near field scanning optical microscope. Surface plasmons excited at all azimuthal directions propagate toward the geometric center and constructively interfere at the focus to create a strongly enhanced evanescent optical "needle" field that is substantially polarized vertically to the plasmonic lens surface. The field enhancement factor can be improved through adding more rings while maintaining the plasmonic focal spot size. Strategy for optimizing the field enhancement factor is studied with both analytical and numerical methods.
Nano Letters 10/2009; 9(12):4320-5. · 13.20 Impact Factor
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ABSTRACT: A plasmonic electro-optic modulator design using an evanescently coupled resonant metal grating is numerically studied in this Letter. Owing to excitation and propagation of long-range surface plasmons between the metal grating nanowires, a deep and narrow reflection dip can be obtained. Improved modulation performance is achieved through decreased damping from large dielectric gaps between the grating nanowires. An optimized electro-optic modulator design with lower insertion loss and low operating voltage is presented.
Optics Letters 04/2008; 33(6):551-3. · 3.40 Impact Factor
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ABSTRACT: Mach-Zehnder interferometers have been the primary type of architecture for construction of polymeric electro-optic modulators. Recent attention has been given to electro-optic modulators in the reflection geometry as well as modulators that employ a resonant cavity to enhance activity or provide for modulator compactness. Most efforts have focused on the Attenuated Total Refelction (ATR) modulators which utilize a guided surface plasmon mode for providing sharply defined angles of incidence at which intesity modulation can be efficiently achieved. This is also the basis of many sensign devices where in both modulation and sensing an active region is placed adjacent to the metal guide. In this work we focus on alternative optical scheems to the ATR for modulation and sensing as well as the possibility of enhanced ATR activity. Resonant cavities are formed using photonic crystals or leaky wave structures which offer the possibiilty of efficient modulation and sensing.
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ABSTRACT: Enhanced electroluminescent efficiency using a deoxyribonucleic acid (DNA)-based biopolymer complex as an electron blocking layer has been demonstrated in both green- and blue-emitting organic light emitting diodes. The resulting bio organic light emitting diodes, or BioLEDs, achieved a maximum luminous efficiency of 8.2 and 0.8 cd/A, respectively, resulting in as much as 10× higher efficiency, 30× brighter output and 3× longer lifetime than their OLED counterparts. In this paper we describe the device fabrication and present the performance of these new structures.
