263 research outputs found
Monolithic whispering-gallery mode resonators with vertically coupled integrated bus waveguides
We report on the realization and optical characterization of a
CMOS-compatible silicon-based microresonator/waveguide coupled system, fully
integrated on a silicon chip. The device uses a vertical coupling scheme
between the resonator and a buried strip waveguide. We demonstrate that its
high optical quality follows from the accurate planarization of the waveguide
topography. More importantly, we demonstrate a wafer-scale mass fabrication of
freestanding planar resonators suspended in air and coupled to the integrated
bus waveguides. A nanometer control of the coupling distances allows for a
precise and selective excitation of different mode families of the resonator.
This opens the door for the realization of stable all-integrated complex
resonator systems for optomechanical and metrological applications, with the
potential to substitute the nowadays intensive use of complicated fiber-taper
coupling schemes.Comment: 3 pages, 3 figure
Photon energy lifter
We propose a time-dependent photonic structure, in which the carrier
frequency of an optical pulse is shifted without changing its shape. The
efficiency of the device takes advantage of slow group velocities of light
attainable in periodic photonic structures. The frequency shifting effect is
quantitatively studied by means of Finite Difference Time Domain simulations
for realistic systems with optical parameters of conventional silicon
technology.Comment: 4 pages 5 figure
Formation of optimal-order necklace modes in one-dimensional random photonic superlattices
We study the appearance of resonantly coupled optical modes, optical
necklaces, in Anderson localized one-dimensional random superlattices through
numerical calculations of the accumulated phase. The evolution of the optimal
necklace order m* shows a gradual shift towards higher orders with increasing
the sample size. We derive an empirical formula that predicts m* and discuss
the situation when in a sample length L the number of degenerate in energy
resonances exceeds the optimal one. We show how the \emph{extra} resonances are
pushed out to the miniband edges of the necklace, thus reducing the order of
the latter by multiples of two.Comment: 4 pages, 4 figure
Permanent mitigation of loss in ultrathin SOI high-Q resonators using UV light
In this paper, we demonstrate strip-loaded guiding optical components
realized on a 27 nm ultra-thin SOI platform. The absence of physically etched
boundaries within the guiding core suppresses majorly the scattering loss, as
shown by us previously for a silicon nitride (SiN) platform [Stefan
\textit{et. al.}, OL 40, 3316 (2015)]. Unexpectedly, the freshly fabricated Si
devices showed large losses of 5 dB/cm, originating from absorption by free
carriers, accumulated under the positively charged SiN loading layer.
We use 254 nm ultraviolet (UV) light exposures to neutralize progressively and
permanently silicon nitride's bulk charge associated with diamagnetic
K+defects. This in turn leads to a net decrease of electron concentration in
the SOI layer, reducing thus the propagation loss down to 0.9 dB/cm. Detailed
MOS-capacitance measurements on test samples were performed to monitor the
UV-induced modification of the electronic properties of the system. The
evolution of loss mitigation was directly monitored both by Beer-Lambert
approach in waveguide transmission experiments, as well as through more
accurate cavity linewidth measurements. In the last case, we demonstrate how
intrinsic cavity 's boost from 60,0000 to up to 500,000 after UV treatment.
Our results may open routes towards engineering of new functionalities in
photonic devices employing UV-modification of space charges and associated
local electric fields, unveil the origin of induced optical nonlinearities in
SiN/Si micro-photonic systems, as well as envisage possible integration
of these with ultra-thin SOI electronics.Comment: 8 pages, 5 figure
Role of edge inclination in optical microdisk resonator for label-free sensing
In this paper we report on the measurement and modelling of enhanced optical
refractometric sensors based on whispering-gallery-modes. The devices under
test are optical microresonators made of silicon nitride on silicon oxide. In
our approach, these microresonators are vertically coupled to a buried
waveguide with the aim of creating integrated and cost-effective devices. The
optimization analysis is a delicate balance of resonance quality factor and
evanescent field overlap with the sorrounding environment to analyze. By
numerical simulations we show that the microdisk thickness is critical to yield
high figure of merit for the sensor, while edge inclination is less important.
We also show that figures of merit as high as 1600/RIU are feasible.Comment: 10 page
A fully integrated high-Q Whispering-Gallery Wedge Resonator
Microresonator devices which posses ultra-high quality factors are essential
for fundamental investigations and applications. Microsphere and microtoroid
resonators support remarkably high Q's at optical frequencies, while planarity
constrains preclude their integration into functional lightwave circuits.
Conventional semiconductor processing can also be used to realize
ultra-high-Q's with planar wedge-resonators. Still, their full integration with
side-coupled dielectric waveguides remains an issue. Here we show the full
monolithic integration of a wedge-resonator/waveguide vertically-coupled system
on a silicon chip. In this approach the cavity and the waveguide lay in
different planes. This permits to realize the shallow-angle wedge while the
waveguide remains intact, allowing therefore to engineer a coupling of
arbitrary strength between these two. The precise size-control and the
robustness against post-processing operation due to its monolithic integration
makes this system a prominent platform for industrial-scale integration of
ultra-high-Q devices into planar lightwave chips.Comment: 6 pages, 4 figure
Optical pulse propagation in a switched-on photonic lattice: Rabi effect with the roles of light and matter interchanged
A light pulse propagating in a suddenly switched on photonic lattice, when
the central frequency lies in the photonic band gap, is an analog of the Rabi
model where the two-level system is the two resonant (i.e. Bragg-coupled)
Fourier modes of the pulse, while the photonic lattice serves as a
monochromatic external field. A simple theory of these Rabi oscillations is
given and confirmed by the numerical solution of the corresponding Maxwell
equations. This is a direct, i.e. temporal, analog of the Rabi effect,
additionally to the spatial analog in optical beam propagation described in
Opt. Lett. 32, 1920 (2007). An additional high-frequency modulation of the Rabi
oscillations reflects the lattice-induced energy transfer between the electric
and magnetic fields of the pulse.Comment: 3 pages, 5 figure
High frequency electro-optic measurement of strained silicon racetrack resonators
The observation of the electro-optic effect in strained silicon waveguides
has been considered as a direct manifestation of an induced
non-linearity in the material. In this work, we perform high frequency
measurements on strained silicon racetrack resonators. Strain is controlled by
a mechanical deformation of the waveguide. It is shown that any optical
modulation vanishes independently of the applied strain when the applied
voltage varies much faster than the carrier effective lifetime, and that the DC
modulation is also largely independent of the applied strain. This demonstrates
that plasma carrier dispersion is responsible for the observed electro-optic
effect. After normalizing out free carrier effects, our results set an upper
limit of to the induced high-speed tensor
element at an applied stress of . This upper limit is about one
order of magnitude lower than the previously reported values for static
electro-optic measurements
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