The increasing demand for early detection of diseases drives the efforts to develop more and more sensitive techniques to detect biomarkers in extremely low concentrations. Electromagnetic modes at the surface of one dimensional photonic crystals, usually called Bloch surface waves, were demonstrated to enhance the resolution and constitute an attractive alternative to surface plasmon polariton optical biosensors. We report on the development of Bloch surface wave biochips operating in both label-free and fluorescence modes and demonstrate their use in ovalbumin recognition assays.
Bloch surface waves (BSW) propagating at the boundary of truncated photonic crystals (1D-PC) have emerged as an attractive approach for label-free sensing in plasmon-like sensor configurations. Due to the very low losses in such dielectric thin film stacks, BSW feature very low angular resonance widths compared to the surface plasmon resonance (SPR) case. Besides label-free operation, the large field enhancement and the absence of quenching allow utilizing BSW coupled fluorescence detection to additionally sense the presence of fluorescent labels. This approach can be adapted to the case of angularly resolved resonance detection, thus giving rise to a combined label-free / labelled biosensor platform. It features a parallel analysis of multiple spots arranged as a one-dimensional array inside a microfluidic channel of a disposable chip. Application of such a combined biosensing approach to the detection of the Angiopoietin-2 cancer biomarker in buffer solutions is reported.
Optical sensors exploiting Bloch surface waves at the truncation edge of one dimensional photonic crystals are used here as a valid alternative to surface plasmon resonance operating in the Kretschmann-Raether configuration, and commonly adopted for label-free optical biosensing. In order to reduce the Bloch surface waves resonance width and increase the resolution it is desirable to work with one dimensional photonic crystals with as small losses as possible. However this makes that the resonances observed in a single polarization reflection scheme are shallow and difficult to track in a sensing experiment. Here we report on the practical implementation of an angularly resolved ellipsometric optical sensing scheme based on Bloch surface waves sustained by tantalia/silica multilayers. The angular resolution is obtained by a focused illumination at fixed wavelength and detecting the angular reflectance spectrum by means of a CMOS array detector. The experimental results, obtained by using one tantalia/silica multilayer with a defined structure, show that the limit of detection can be pushed below 2.1x10-7RIU/Hz1/2.
Optoelectronic properties of Er3+-doped slot waveguides electrically driven are presented. The active waveguides have been coupled to a Si photonic circuit for the on-chip distribution of the electroluminescence (EL) signal at 1.54 μm. The Si photonic circuit was composed by an adiabatic taper, a bus waveguide and a grating coupler for vertical light extraction. The EL intensity at 1.54 μm was detected and successfully guided throughout the Si photonic circuit. Different waveguide lengths were studied, finding no dependence between the waveguide length and the EL signal due to the high propagation losses measured. In addition, carrier injection losses have been observed and quantified by means of time-resolved measurements, obtaining variable optical attenuation of the probe signal as a function of the applied voltage in the waveguide electrodes. An electro-optical modulator could be envisaged if taking advantage of the carrier recombination time, as it is much faster than the Er emission lifetime.
In this work, the optoelectronic properties of silicon light emitting field-effect transistors (LEFETs) have been
investigated. The devices have been fabricated with silicon nanocrystals in the gate oxide and a
semitransparent polycrystalline silicon gate. We compare the properties of LEFET with a more conventional
MOS-LED (two-terminal light-emitting capacitor) with the same active material. The ~45 nm thick gate siliconrich
oxide is deposited in a size-controlled multilayer geometry by low pressure chemical vapor deposition
using standard microelectronic processes in a CMOS line. The multilayer stack is formed by layers of silicon
oxide and silicon rich silicon oxide. The nanocrystal size and the tunneling barrier width are controlled by the
thickness of silicon-rich silicon oxide and stochiometric silicon oxide layers, respectively. The silicon
nanocrystals have been characterized by means of spectrally and time resolved photoluminescence, high
resolution TEM, and x-ray photoelectron spectroscopy. Resistivity of the devices, capacitance, and
electroluminescence under direct and pulsed injection current scheme have been studied and here reported.
The optical power density and the external quantum efficiency of the LEFETs will be compared with the MOSLED
results. This study will help to develop practical optoelectronic and photonic devices via accurate
modeling and engineering of charge transport and exciton recombination in silicon nanocrystal arrays.
The convergence of photonics and microelectronics within a single chip is still lacking of a monolithical on-chip optical
amplifier. Rare-earth doped slot waveguides show a large potential as on-chip source. Slot waveguides with silicon
nanocrystals embedded in a dielectric host matrix can increase the light confinement in the active layer and allow
electrical injection. In this work, horizontal slot waveguides formed by two thick silicon layers separated by a thin
erbium doped silicon rich silicon oxide layer are studied as on-chip optical amplifiers. The waveguides are grown in a
CMOS line with the active material grown by low-pressure chemical vapor deposition. Optical tests are performed and
light propagation in the slot waveguides is observed. Using the cut-back technique, spectra propagation losses are
evaluated. Room temperature electroluminescence is observed at 1.54 μm. Transmitted optical signal resonant with Er
absorption is studied as a function of the injected current for different probing laser wavelengths.
Materials used as luminescent down shifters (LDS) have to absorb light effectively in the spectral area where solar cells
have poor internal quantum efficiency. At the same time these materials have to emit most of the absorbed spectral
powers at lower energies where the internal quantum efficiency of the solar cell is close to the maximum. The effects of
silicon nanocrystals prepared by thermal treatment of a silicon-rich-oxide (SRO) layer on the efficiency of c-Si cells are
investigated in this paper. The SRO layer is characterized by a high photoluminescence peak at around 800 nm.
Influence of the active layer on light transmission and on the modification of the optical spectra due to
photoluminescence generation has been determined with the help of optical measurements and transfer matrix
simulations. The solar cell efficiency for cells with and without down-shifting layer were measured under illumination
with AM1.5G solar spectrum and compared with the simulations. Finally, we model the behavior of cells with and
without LDS layer showing that a cell with LDS suffers less from bad surface passivation.