Nanoscale Optical Waveguides Research Articles

Nanomotion of Micro-Objects Driven by Light-Induced Elastic Waves on Solid Interfaces

It has been recently reported that elastic waves induced by nanosecond light pulses can be used to drive nanomotion of micro-objects on frictional solid interfaces, a challenging task for traditional techniques using tiny optical force. In this technique, the main physical quantities and parameters involved are temporal width and energy of light pulses, thermal heating and cooling time, friction force, and elastic waves. Despite a few experimental observations based on microfiber systems, a microscopic theory, which reveals how these quantities collaboratively enable motion of the micro-objects and derives what the underlying manipulation principles emerge, is absent. In this paper, a comprehensive theoretical analysis---centralized around the above listed physical quantities, and illuminated by a single-friction-point model in conjunction with numerical simulations---is established to pedagogically clarify the physics. Our results reveal the two essential factors in this technique: (1) the use of short light pulses for rapid thermal expansion overwhelming friction resistance and (2) the timescale asymmetry in thermal heating and cooling for accumulating a net sliding distance. Moreover, we examine the effects of spatially distributed friction beyond the single-friction-point consideration, and show ``tug-of-war''-like friction stretching in the driving process. Given these insights, we positively predict that this elastic-wave-based manipulation principle could be directly translated to micro- and nanoscale optical waveguides on optical chips, and propose a practical design. We wish that these results offer theoretical guidelines for ongoing efforts of optical manipulation on solid interfaces with light-induced elastic waves.

Optical properties of nanowires based on a blend of poly (9,9-dioctylfluorene) [PFO] and poly(9,9-dioctyl fluorene-alt-benzothiadiazole) [F8BT

Near-field and far-field optical microscopy are used to study the optical properties of nanowires based on a blend of 95% poly (9,9-dioctylfluorene) [PFO] doped with 5% poly (9,9-dioctylfluorene-alt-benzothiadiazole) [F8BT]. Single nanowires were imaged and optical investigations revealed that they act as nanoscale optical waveguides. Investigation using polarization-resolved far-field PL spectroscopy revealed emission from the nanowires was strongly anisotropic having preferred axial polarization. This suggests that a significant number of the polymer chains are oriented along the nanowire axis.

Bright Quadruplex Nanostructures Using Masked Porphyrin Lanterns

DNA-based self-assembly, that incorporates numerous dyes, is an attractive modality to construct 2D and 3D nanoscale structures with photonic properties. Such assemblies have potential applications in multiple arenas, including as nanoscale optical waveguides for photonic circuits, synthetic light-harvesting materials, and signal enhanced fluorescent devices. However, densely arranged dyes tend to aggregate (especially in water) leading to attenuated photophysical properties. Additionally, increasing dye density can substantially compromise the DNA assembly mode due to competing hydrophobic interactions. In this seminar we will illustrate a “tether, mask, and assemble” strategy that first incorporates the porphyrin dye onto DNA and then masks the dye (forming a porphyrin lantern state wherein detrimental aggregation is negated) and finally assembles the DNA into bright nanostructures. We particularly focus on using versatile, guanine-rich, sequences that can form cyclic and cylindrically arranged porphyrin lanterns.

EXACT SOLUTIONS AND DYNAMICS OF THE RAMAN SOLITON MODEL IN NANOSCALE OPTICAL WAVEGUIDES, WITH METAMATERIALS, HAVING PARABOLIC LAW NON-LINEARITY

This paper investigate the Raman soliton model in nanoscale optical waveguides, with metamaterials, having parabolic law non-linearity by using the method of dynamical systems. The functions $ q(x, t) = \phi(\xi)\exp(i(-kx+\omega t)) $ are solutions of the equation (1.1) that governs the propagation of Raman solitons through optical metamaterials, where $ \xi = x-vt $ and $ \phi(\xi) $ in the solutions satisfy a singular planar dynamical system (1.5) which has two singular straight lines. By using the bifurcation theory method of dynamical systems to the equation of $ \phi(\xi) $, bifurcations of phase portraits for this dynamical system are obtained under 28 different parameter conditions. Based on those phase portraits, 62 exact solutions of system (1.5) including periodic solutions, heteroclinic and homoclinic solutions, periodic peakons and peakons as well as compacton solutions are derived.

Exact Solutions and Dynamics of the Raman Soliton Model in Nanoscale Optical Waveguides, with Metamaterials, Having Polynomial Law Nonlinearity

Raman soliton model in nanoscale optical waveguides, with metamaterials, having polynomial law nonlinearity is investigated by the method of dynamical systems. The functions [Formula: see text] in the solutions [Formula: see text] [Formula: see text] satisfy a singular planar dynamical system having two singular straight lines. By using the bifurcation theory method of dynamical systems to the equations of [Formula: see text], under 23 different parameter conditions, bifurcations of phase portraits and exact periodic solutions, homoclinic and heteroclinic solutions, periodic peakons and peakons as well as compacton solutions for this planar dynamical system are obtained. 92 exact explicit solutions of system (6) are derived.

Dipole force free optical control and cooling of nanofiber trapped atoms.

The evanescent field surrounding nanoscale optical waveguides offers an efficient interface between light and mesoscopic ensembles of neutral atoms. However, the thermal motion of trapped atoms, combined with the strong radial gradients of the guided light, leads to a time-modulated coupling between atoms and the light mode, thus giving rise to additional noise and motional dephasing of collective states. Here, we present a dipole force free scheme for coupling of the radial motional states, utilizing the strong intensity gradient of the guided mode and demonstrate all-optical coupling of the cesium hyperfine ground states and motional sideband transitions. We utilize this to prolong the trap lifetime of an atomic ensemble by Raman sideband cooling of the radial motion which, to the best of our knowledge, has not been demonstrated in nano-optical structures previously. This Letter points towards full and independent control of internal and external atomic degrees of freedom using guided light modes only.

Raman solitons in nanoscale optical waveguides, with metamaterials, having polynomial law non-linearity

This paper reports bright Raman soliton solutions in optical metamaterials. The polynomial law and triple law non-linearity are discussed. Travelling wave hypothesis is employed to conduct the mathematical analysis. Implicit solutions in terms of elliptic integral of the third kind are obtained. The analytical results are supplemented with numerical simulations.

Brillouin scattering self-cancellation.

The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon–phonon interaction, enhancing or suppressing it.

Energy transfer effect of hybrid organic rubrene nanorod with CdSe/ZnS quantum dots: Application to optical waveguiding modulators

Organic rubrene (5,6,11,12-tetraphenyltetracene) nanorods (NRs) were fabricated through the physical vapor transport method for the study of active fluorescence optical waveguiding and its modulation. The functionalized CdSe/ZnS quantum dots (QDs) with blue and green emissions were partially attached to the surface of the rubrene NR. Using a high resolution laser confocal microscope (LCM), the nanoscale photoluminescence (PL) intensity of the pristine rubrene portion of the hybrid NR/QDs was observed to be considerably enhanced after it was attached with blue (or green) QDs. The nanoscale optical waveguiding characteristics of the hybrid NR/QDs were investigated in terms of the output LCM PL spectra as a function of propagation distance. We observed more efficient optical waveguiding characteristics from the hybrid rubrene NR/blue-QDs than from the pristine NR and the hybrid rubrene NR/green-QDs. These results can be analyzed in terms of the higher Förster resonance energy transfer efficiency for hybrid rubrene NR/blue-QDs system. The results and analysis were supported by a drastic decrease of exciton lifetime of QDs in the hybrid region as measured by time-resolved PL decay curves.

Identification of Higher Order Long-Propagation-Length Surface Plasmon Polariton Modes in Chemically Prepared Gold Nanowires

A comprehensive understanding of the type of modes and their propagation length for surface plasmon polaritons (SPPs) in gold nanowires is essential for potential applications of these materials as nanoscale optical waveguides. We have studied chemically synthesized single gold nanowires by a novel technique called bleach-imaged plasmon propagation (BlIPP), which relies on the plasmonic near-field induced photobleaching of a dye to report the SPP propagation in nanowires. We observed a much longer propagation length of 7.5 ± 2.0 μm at 785 nm compared to earlier reports, which found propagation lengths of ~2.5 μm. Finite difference time domain simulations revealed that the bleach-imaged SPP is a higher order m = 1 mode and that the lowest order m = 0 mode is strongly quenched due to the loss to the dye layer and cannot be resolved by BlIPP. A comparative assessment of BlIPP with direct fluorescence imaging furthermore showed that the significant difference in propagation lengths obtained by these two techniques can be attributed to the difference in their experimental conditions, especially to the difference in thickness of the dye layer coating on the nanowire. In addition to identifying a higher order SPP mode with long propagation length, our study infers that caution must be taken in selecting indirect measurement techniques for probing SPP propagation in nanoscale metallic waveguides.

Surface plasmon polariton analogue to Young's double-slit experiment

When a light wave strikes a metal film it can, under appropriate conditions, excite a surface plasmon polariton (SPP)--a surface electromagnetic wave that is coupled to the free electrons in the metal. Such SPPs are involved in a wide range of phenomena, including nanoscale optical waveguiding, perfect lensing, extraordinary optical transmission, subwavelength lithography and ultrahigh-sensitivity biosensing. However, before the full potential of technology based on SPPs (termed 'plasmonics') can be realized, many fundamental questions regarding the interaction between light and matter at the nanoscale need to be answered. For over 200 years, Young's double-slit experiment has been a valuable pedagogical tool for demonstrating the wave nature of light. Here, we perform a double-slit experiment with SPPs to reveal the strong analogy between SPP propagation along the surface of metallic structures and light propagation in conventional dielectric components (such as glass waveguides). This allows us to construct a general framework to describe the propagation, diffraction and interference of SPPs. It also suggests that there is an effective diffraction limit for the lateral confinement of SPPs on metal stripe waveguides, and justifies the use of well-developed concepts from conventional optics and photonics in the design of new plasmonic devices.