62 research outputs found
The role of index contrast in the efficiency of absoprtion and emission of a luminescent particle near a slab waveguide
Enhanced spontaneous raman signal collected evanescently by silicon nitride slot waveguides
We investigate the effect of waveguide geometry on the conversion efficiency of Raman signals collected by integrated photonic waveguides. Compared to strip-type photonic wires, we report a six-fold increase in conversion efficiency for silicon-nitride slot-waveguides
Enhancement of raman scattering efficiency by a metallic nano-antenna on top of a high index contrast waveguide
We theoretically study coupling of dipole radiation into integrated Si3N4 strip waveguides functionalized with a nanoplasmonic antenna. This structure enables efficient coupling of enhanced Raman signals into the fundamental TE-mode of the waveguide
Surface enhanced Raman spectroscopy on single mode nanophotonic-plasmonic waveguides
We analyze the generation of Surface Enhanced Raman Spectroscopy signals from integrated bowtie antennas, excited and collected by a single mode silicon nitride waveguide, and discuss strategies to enhance the Signal-to-Noise Ratio
Surface enhanced Raman spectroscopy using a single mode nanophotonic-plasmonic platform
Surface Enhanced Raman Spectroscopy (SERS) is a well-established technique
for enhancing Raman signals. Recently photonic integrated circuits have been
used, as an alternative to microscopy based excitation and collection, to probe
SERS signals from external metallic nanoparticles. However, in order to develop
quantitative on-chip SERS sensors, integration of dedicated nanoplasmonic
antennas and waveguides is desirable. Here we bridge this gap by demonstrating
for the first time the generation of SERS signals from integrated bowtie
nanoantennas, excited and collected by a single mode waveguide, and rigorously
quantify the enhancement process. The guided Raman power generated by a
4-Nitrothiophenol coated bowtie antenna shows an 8 x 10^6 enhancement compared
to the free-space Raman scattering. An excellent correspondence is obtained
between the theoretically predicted and observed absolute Raman power. This
work paves the way towards fully integrated lab-on-a-chip systems where the
single mode SERS-probe can be combined with other photonic, fluidic or
biological functionalities.Comment: Submitted to Nature Photonic
Silicon-nitride waveguides for on-chip Raman spectroscopy
The evanescent tail of the guided modes can efficiently excite Raman active molecules located in the cladding of a waveguide. Similarly, a significant fraction of the total emitted Stokes power is evanescently coupled to the same mode. Further, the enhancement effects inherent to the waveguide, alongside with the long interaction length, lead to an increased light-matter interaction, resulting in a higher sensitivity as required by spectroscopic applications, especially in the context of Raman spectroscopy. We calculate the spontaneous Raman scattering efficiency as a function of siliconnitride strip waveguide dimensions and show that under typical conditions, the overall efficiency is approximately two orders of magnitude higher than in confocal configuration in the free space. We also report the experimental demonstration of the use of silicon-nitride based photonic waveguides in a lab-on-a-chip context for Raman spectroscopy. To the best of our knowledge, this is the first demonstration of Raman spectroscopy using photonic waveguides
Near-infrared grating couplers for silicon nitride photonic wires
Silicon nitride is a promising high-index material for dense photonic circuits and applications in the visible-midinfrared wavelength regime. Design, fabrication, and optical characterization of silicon nitride waveguides at visible-near-infrared wavelength are presented. Finally, design and experimental results are presented for the first time for linear and focused grating couplers (GCs) at near-infrared wavelength (900 nm) for plasma-enhanced chemical vapor deposition silicon nitride wires (220 x 500 nm) and compared with theoretical simulations. An experimental efficiency of 5.7 and 6.5 dB and 1-dB bandwidth of 26 and 40 nm are reported for the linear and focused GCs, respectively
Determining size of an optically trapped particle via modulated Raman spectroscopy
The average Raman signal power obtained in a modulated optical trap is
dependent on the Brownian motion - therefore hydrodynamic properties of the
trapped particle. Hence, in addition to the molecular properties obtained from
the Raman signal, it is possible to study hydrodynamic properties (e.g. size)
of the particle by analyzing the change in the average Raman power as a
function of modulation frequency. Our results, based on the over-damped
Langevin equation, show that several minimas exist for the Raman signal at
unique modulating frequencies for a given particle size and signal acquisition
time. In typical experimental conditions, such minimas can be as low as 50% of
the Raman signal in an unmodulated trap
Nanophotonic waveguide enhanced Raman spectroscopy of biological submonolayers
Characterizing a monolayer of biological molecules has been a major
challenge. We demonstrate nanophotonic wave-guide enhanced Raman spectroscopy
(NWERS) of monolayers in the near-infrared region, enabling real-time
measurements of the hybridization of DNA strands and the density of
sub-monolayers of biotin-streptavidin complex immobilized on top of a photonics
chip. NWERS is based on enhanced evanescent excitation and collection of
spontaneous Raman scattering near nanophotonic waveguides, which for a one
centimeter silicon nitride waveguide delivers a signal that is more than four
orders of magnitude higher in comparison to a confocal Raman microscope. The
reduced acquisition time and specificity of the signal allows for a
quantitative and real-time characterization of surface species, hitherto not
possible using Raman spectroscopy. NWERS provides a direct analytic tool for
monolayer research and also opens a route to compact microscope-less
lab-on-a-chip devices with integrated sources, spectrometers and detectors
fabricated using a mass-producible CMOS technology platform
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