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ABSTRACT: We show that in high-index-contrast nanoscale waveguides counter propagating waves can posses distinct spatial near-field profiles. Using transmission-based near-field scanning optical microscopy (TraNSOM), we identify and map the unique near-field intensity distributions of these counter-propagating modes in a single-mode silicon waveguide. Based on this phenomenon, we design and simulate an integrated device 45 µm in length that selectively attenuates reflected light with an insertion loss of -3.6 dB and an extinction of greater than -20 dB.
Optics Express 09/2011; 19(19):18380-92. · 3.59 Impact Factor
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ABSTRACT: On-chip photonic networks have the potential to transmit and route information more efficiently than electronic circuits. Recently, a number of silicon-based optical devices including modulators, buffers, and wavelength converts have been reported. However, a number of technical challenges need to be overcome before these devices can be combined into network-level architectures. In particular, due to the high refractive index contrast between the core and cladding of semiconductor waveguides, nanoscale defects along the waveguide often scatter light into the backward-propagating mode. These reflections could result in unwanted feedback to optical sources or crosstalk in bidirectional interconnects such as those employed in fiber-optic networks. It is often assumed that these reflected waves spatially overlap the forward-propagating waves making it difficult to implement optical circulators or isolators which separate or attenuate light based on its propagation direction. Here, we individually identify and map the near-field mode profiles of forward-propagating and reflected light in a single-mode silicon waveguide using Transmission-based near-field scanning optical microscopy (TraNSOM). We show that unlike fiber-optic waveguides, the high-index-contrast and nanoscale dimensions of semiconductor waveguides create counter propagating waves with distinct spatial near-field profiles. These near-field differences are a previously-unobserved consequence of nanoscale light confinement and could provide a basis for novel elements to filter forward-propagating from reflected light.
09/2010;
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ABSTRACT: We demonstrate that optomechanical devices can exhibit nonreciprocal behavior when the dominant light-matter interaction takes place via a linear momentum exchange between light and the mechanical structure. As an example, we propose a microscale optomechanical device that can exhibit a nonreciprocal behavior in a microphotonic platform operating at room temperature. We show that, depending on the direction of the incident light, the device switches between a high and low transparency state with more than a 20 dB extinction ratio.
Physical Review Letters 06/2009; 102(21):213903. · 7.37 Impact Factor
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ABSTRACT: We fabricate high-Q arsenic triselenide glass microspheres through a three-step resistive heating process. We demonstrate quality factors greater than 2 x 10(6) at 1550 nm and achieve efficient coupling via a novel scheme utilizing index-engineered unclad silicon nanowires. We find that at powers above 1 mW the microspheres exhibit high thermal instability, which limits their application for resonator-enhanced nonlinear optical processes.
Optics Express 05/2009; 17(8):5998-6003. · 3.59 Impact Factor
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ABSTRACT: We demonstrate low loss silicon waveguides fabricated without any silicon etching. We define the waveguides by selective oxidation which produces ultra-smooth sidewalls with width variations of 0.3 nm. The waveguides have a propagation loss of 0.3 dB/cm at 1.55 microm. The waveguide geometry enables low bending loss of approximately 0.007 dB/bend for a 90 degrees bend with a 50 microm bending radius.
Optics Express 04/2009; 17(6):4752-7. · 3.59 Impact Factor
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ABSTRACT: From first principles we develop figures of merit to determine the gain experienced by the guided mode and the lasing threshold for devices based on high-index-contrast waveguides. We show that as opposed to low-index-contrast systems, this quantity is not equivalent to the power confinement since in high-index-contrast structures the electric and magnetic field distributions cannot be related by proportionality constant. We show that with a slot waveguide configuration it is possible to achieve more gain than one would expect based on the power confinement in the gain media. Using the figures of merit presented here we optimize a slot waveguide geometry to achieve low-threshold lasing and discuss the fabrication tolerances of such a design.
Optics Express 11/2008; 16(21):16659-69. · 3.59 Impact Factor
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ABSTRACT: We demonstrate a chip-scale photonic system for the room-temperature detection of gas composition and pressure using a slotted silicon microring resonator. We measure shifts in the resonance wavelength due to the presence and pressure of acetylene gas and resolve differences in the refractive index as small as 10(-4) in the near-IR. The observed sensitivity of this device (enhanced due to the slot-waveguide geometry) agrees with the expected value of 490 nm/refractive index unit.
Optics Express 04/2008; 16(6):4296-301. · 3.59 Impact Factor
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ABSTRACT: We demonstrate long-range control of the radiative lifetime of a silicon optical nanocavity using a metallic atomic force microscope probe. We extract changes in the radiative lifetime from changes in the cavity's transmittivity resulting from probe-cavity interaction over distances of several optical wavelengths. Analogous to atomic systems, the cavity acts as an individual radiating dipole with a radiative rate that is modified by a metallic interface.
Physical Review Letters 03/2008; 100(4):043902. · 7.37 Impact Factor
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ABSTRACT: We show the existence of direct photonic transitions between modes of a silicon optical microcavity spaced apart in wavelength by over 8 nm. This is achieved by using ultrafast tuning of the refractive index of the cavity over a time interval that is comparable to the inverse of the frequency separation of modes. The demonstrated frequency mixing effect, i.e., the transitions between the modes, would enable on-chip silicon comb sources which can find wide applications in optical sensing, precise spectroscopy, and wavelength-division multiplexing for optical communications and interconnects.
Physical Review Letters 02/2008; 100(3):033904. · 7.37 Impact Factor
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ABSTRACT: Through full-vectorial simulations and analytical models, we investigate the role of radiation and surface plasmon polaritons (SPP) in the optical interaction between a nano-slit and a parallel nano-groove on a metal surface. We quantitatively confirm the radiaton as the interaction mechanism in perfect electrical conductors (PEC), and verify the role of radiation and SPP in the slit-groove interaction in silver. While the contribution of SPP dominates for the nano-slit and nano-groove placed far apart, the radiation plays a significant role for the nano-slit and nano-groove with smaller separations comparable to one wavelength. We present the first quantitative of the individual contributions of the radiation and SPP on the transmission through the nano-slit.
Optics Express 01/2007; 14(26):12629-36. · 3.59 Impact Factor
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ABSTRACT: We demonstrate a new technique for high resolution imaging of near field profiles in highly confining photonic structures. This technique, Transmission-based Near-field Scanning Optical Microscopy (TraNSOM), measures changes in transmission through a waveguide resulting from near field perturbation by a scanning metallic probe. Using this technique we compare different mode polarizations and measure a transverse optical decay length of lambda/15 in sub-micron Silicon On Insulator (SOI) waveguides. These measurements compare well to theoretical results.
Optics Express 11/2006; 14(22):10588-95. · 3.59 Impact Factor
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ABSTRACT: We theoretically demonstrate a mechanism for reduction of mode volume in high index contrast optical microcavities to below a cubic half wavelength. We show that by using dielectric discontinuities with subwavelength dimensions as a means of local field enhancement, the effective mode volume (V(eff)) becomes wavelength independent. Cavities with V(eff) on the order of 10(-2)(lambda/2n)(-3) can be achieved using such discontinuities, with a corresponding increase in the Purcell factor of nearly 2 orders of magnitude relative to previously demonstrated high index photonic crystal cavities.
Physical Review Letters 10/2005; 95(14):143901. · 7.37 Impact Factor
