Bloch mode selection in silicon photonic crystal microring resonators.

A novel method of selecting a subset of Bloch modes in silicon-based photonic crystal microring resonators (PhCR)s is demonstrated. Bloch modes in the PhCR are calculated, and their intensity beating patterns are analyzed. Based on the different spatial intensity distribution for each resonance, a subset of resonances is out-coupled using an output coupler waveguide (CWG) which is positioned at an angle θ=90° with respect to the input CWG.

Photonic crystal microring resonator for label-free biosensing.

A label-free optical biosensor based on a one-dimensional photonic crystal microring resonator with enhanced light-matter interaction is demonstrated. More than a 2-fold improvement in volumetric and surface sensing sensitivity is achieved compared to conventional microring sensors. The experimental bulk detection sensitivity is ~248nm/RIU and label-free detection of DNA and proteins is reported at the nanomolar scale.

Numerical study of sensitivity enhancement in a photonic crystal microcavity biosensor due to optical forces.

Photonic crystal microcavity biosensors can detect single biomolecules, but reliance on diffusion from microfluidic flow for particle delivery limits the minimum detectable particle concentration. Here the particle equation of motion is solved to find the sensitivity enhancement due to optical forces. The enhancement is examined for a range of parameters, including input optical power, fluid flow rate, device quality factor, and particle size.

Plasmonic effects in ultrathin amorphous silicon solar cells: performance improvements with Ag nanoparticles on the front, the back, and both.

Thin-film hydrogenated amorphous silicon (a-Si:H) solar cells that are free-standing over a 2x2 mm area have been fabricated with thicknesses of 150 nm, 100 nm, and 60 nm. Silver nanoparticles (NPs) created on the front and/or back surfaces of the solar cells led to improvement in performance measures such as current density, overall efficiency, and external quantum efficiency. The effect of changing silver nanoparticle size and incident light angle was tested.

Influence of silicon dioxide capping layers on pore characteristics in nanocrystalline silicon membranes.

Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications.

Highly porous silicon membranes fabricated from silicon nitride/silicon stacks.

Nanopore formation in silicon films has previously been demonstrated using rapid thermal crystallization of ultrathin (15 nm) amorphous Si films sandwiched between nm-thick SiO2 layers. In this work, the silicon dioxide barrier layers are replaced with silicon nitride, resulting in nanoporous silicon films with unprecedented pore density and novel morphology. Four different thin film stack systems including silicon nitride/silicon/silicon nitride (NSN), silicon dioxide/silicon/silicon nitride (OSN), silicon nitride/silicon/silicon dioxide (NSO), and silicon dioxide/silicon/silicon dioxide (OSO) are tested under different annealing temperatures.

Suppression of free carrier absorption in silicon using multislot SiO2/nc-Si waveguides.

Free carrier absorption (FCA) in silicon is the major obstacle toward achieving optical gain in Si nanostructure systems. In this Letter, we present experimental results of pump-induced loss for TE and TM polarization in multislot SiO2/nc-Si waveguides. Continuous wavelength and ultrafast studies of carriers excited in the nc-Si multilayers reveal strong suppression of transmission loss related to FCA in Si nanostructures for TM-polarized probe light.

High-performance, low-voltage electroosmotic pumps with molecularly thin silicon nanomembranes.

We have developed electroosmotic pumps (EOPs) fabricated from 15-nm-thick porous nanocrystalline silicon (pnc-Si) membranes. Ultrathin pnc-Si membranes enable high electroosmotic flow per unit voltage. We demonstrate that electroosmosis theory compares well with the observed pnc-Si flow rates.

Selective virus detection in complex sample matrices with photonic crystal optical cavities.

Rapid, sensitive, and selective detection of viruses is critical for applications in medical diagnostics, biosecurity, and environmental safety. In this article, we report the application of a point-defect-coupled W1 photonic crystal (PhC) waveguide biosensor to label-free optical detection of viruses. Fabricated on a silicon-on-insulator (SOI) substrate using electron-beam (e-beam) lithography and reactive-ion-etching, the PhC sensing platform allows optical detection based on resonant mode shifts in response to ambient refractive index changes produced by infiltration of target biomaterial within the holes of the PhC structure.

1-D and 2-D photonic crystals as optical methods for amplifying biomolecular recognition.

Label-free sensing strategies are an intensely studied and increasingly used alternative to signal amplification via fluorescent labels and enzymatic methods. This article discusses one class of optical sensors, termed "photonic crystals", that effectively amplify binding events (such as analyte capture) via strong light-matter interactions.

Slow-light dispersion in periodically patterned silicon microring resonators.

We demonstrate a novel periodically patterned ring resonator evanescently coupled with a coupler waveguide (CWG) on a silicon-on-insulator platform. In order to optimize the coupling, we phase match the ring resonator and the CWG by tuning the width of the CWG. In the transmission spectra, we measure a high extinction ratio of more than 20 dB and achieve a group index of ~20 in the slow-light regime.

Experimental demonstration of evanescent coupling and photon confinement in oxide-clad silicon microcavities.

For use in on-chip and integrated applications, photonic crystals must not only be embedded in silica but must also be able to easily integrate with other photonic devices. Here we provide an experimental demonstration of resonance in a SiO(2)-clad two-dimensional photonic crystal microcavity that is coupled to standard Si strip waveguides. We further show that well over 90% of the resonant field is confined within the cavity's silicon layer, which is necessary if the microcavity is to be used as a high-efficiency electro-optic modulator.

Silicon photonic crystal nanocavity-coupled waveguides for error-corrected optical biosensing.

A photonic crystal (PhC) waveguide based optical biosensor capable of label-free and error-corrected sensing was investigated in this study. The detection principle of the biosensor involved shifts in the resonant mode wavelength of nanocavities coupled to the silicon PhC waveguide due to changes in ambient refractive index. The optical characteristics of the nanocavity structure were predicted by FDTD theoretical methods.

High-performance separation of nanoparticles with ultrathin porous nanocrystalline silicon membranes.

Porous nanocrystalline silicon (pnc-Si) is a 15 nm thin free-standing membrane material with applications in small-scale separations, biosensors, cell culture, and lab-on-a-chip devices. Pnc-Si has already been shown to exhibit high permeability to diffusing species and selectivity based on molecular size or charge. In this report, we characterize properties of pnc-Si in pressurized flows.

Ultra-low power modulators using MOS depletion in a high-Q SiO₂-clad silicon 2-D photonic crystal resonator.

In modulators that rely on changing refractive index, switching energy is primarily dependent upon the volume of the active optical mode. Photonic crystal microcavities can exhibit extremely small mode volumes on the order of a single cubic wavelength with Q values above 10(6). In order to be useful for integration, however, they must be embedded in oxide, which in practice reduces Q well below 10(3), significantly increasing switching energy.

Pore size control of ultrathin silicon membranes by rapid thermal carbonization.

Rapid thermal carbonization in a dilute acetylene (C(2)H(2)) atmosphere has been used to chemically modify and precisely tune the pore size of ultrathin porous nanocrystalline silicon (pnc-Si). The magnitude of size reduction was controlled by varying the process temperature and time. Under certain conditions, the carbon coating displayed atomic ordering indicative of graphene layer formation conformal to the pore walls.

Ion-selective permeability of an ultrathin nanoporous silicon membrane as probed by scanning electrochemical microscopy using micropipet-supported ITIES tips.

We report on the application of scanning electrochemical microscopy (SECM) to the measurement of the ion-selective permeability of porous nanocrystalline silicon membrane as a new type of nanoporous material with potential applications in analytical, biomedical, and biotechnology device development. The reliable measurement of high permeability in the molecularly thin nanoporous membrane to various ions is important for greater understanding of its structure-permeability relationship and also for its successful applications. In this work, this challenging measurement is enabled by introducing two novel features into amperometric SECM tips based on the micropipet-supported interface between two immiscible electrolyte solutions (ITIES) to reveal the important ion-transport properties of the ultrathin nanopore membrane.

Ultrafast optical switching based on nonlinear polarization rotation in silicon waveguides.

We experimentally realize ultrafast all-optical switching in the 1.5-microm spectral region using cross-phase modulation inside a 5-mm long silicon waveguide. Modulation depths of up to 90% and switching window durations approximately 1 ps are achieved using 500-fs pump pulses with energies below 10 pJ.

Optical switching using nonlinear polarization rotation inside silicon waveguides.

We study the nonlinear polarization rotation induced by a pump pulse on a probe beam through cross-phase modulation inside a silicon waveguide and show that this phenomenon can be used to realize a fast Kerr shutter in spite of the free-carrier effects and walk-off. We show that free carriers generated by the pump pulse through two-photon absorption affect the switching process considerably, especially with the interaction of walk-off effects. However, numerical simulations reveal that their impact is not detrimental for short pump pulses.

Birefringence and optical power confinement in horizontal multi-slot waveguides made of Si and SiO2.

Through simulations and measurements, we show that in multi-slot thin film waveguides, the TM polarized modes can be confined mostly in the low refractive index layers of the waveguide. The structure consisted of alternating layers of a-Si and SiO(2), in the thickness range between 3 and 40 nm, for which the slots were the SiO(2) layers. Simulations were performed using the transfer matrix method and experiments using the m-line technique at 1.

A structure-permeability relationship of ultrathin nanoporous silicon membrane: a comparison with the nuclear envelope.

We report on a simple, quantitative relationship between structure and permeability of a novel ultrathin nanoporous membrane based on nanocrystalline silicon. Large permeability of the free-standing nanomembrane to Ru(NH3)63+, O2, or 1,1'-ferrocenedimethanol, which was able to be measured for the first time by employing scanning electrochemical microscopy, is proportional to the density (67 mum-2) and average radius (5.6 nm) of nanopores.

Nanoscale microcavity sensor for single particle detection.

Recently we demonstrated a biosensor based on a two-dimensional photonic crystal microcavity for detection of proteins. We present a theoretical and experimental study of a modified structure for single particle detection. With an active sensing volume of approximately 0.

Optical solitons in a silicon waveguide.

We observe, for the first time to our knowledge, the formation of optical solitons inside a short silicon waveguide (only 5 mm long) at subpicojoule pulse energy levels. We measure a significant spectral narrowing in the anomalous-dispersion regime of such a waveguide, in contrast to all previous reported experiments. The extent of spectral narrowing depends on the carrier wavelength of input pulses, and the observed spectrum broadens in the normal-dispersion region.

Two-dimensional silicon photonic crystal based biosensing platform for protein detection.

We theoretically and experimentally demonstrate an ultrasensitive two-dimensional photonic crystal microcavity biosensor. The device is fabricated on a silicon-on-insulator wafer and operates near its resonance at 1.58 microm.

Charge- and size-based separation of macromolecules using ultrathin silicon membranes.

Commercial ultrafiltration and dialysis membranes have broad pore size distributions and are over 1,000 times thicker than the molecules they are designed to separate, leading to poor size cut-off properties, filtrate loss within the membranes, and low transport rates. Nanofabricated membranes have great potential in molecular separation applications by offering more precise structural control, yet transport is also limited by micrometre-scale thicknesses. This limitation can be addressed by a new class of ultrathin nanostructured membranes where the membrane is roughly as thick (approximately 10 nm) as the molecules being separated, but membrane fragility and complex fabrication have prevented the use of ultrathin membranes for molecular separations.