34 research outputs found
Two regimes of confinement in photonic nanocavities: bulk confinement versus lightning rods
We present a theoretical study of dielectric bowtie cavities and show that
they are governed by two essentially different confinement regimes. The first
is confinement inside the bulk dielectric and the second is a local
lightning-rod regime where the field is locally enhanced at sharp corners and
may yield a vanishing mode volume without necessarily enhancing the mode inside
the bulk dielectric. We show that while the bulk regime is reminiscent of the
confinement in conventional nanocavities, the most commonly used definition of
the mode volume gauges in fact the lightning-rod effect when applied to
ultra-compact cavities, such as bowties. Distinguishing between these two
regimes will be crucial for future research on nanocavities, and our insights
show how to obtain strongly enhanced light-matter interaction over large
bandwidths.Comment: 9 pages, 5 figures, 39 reference
Impact of transduction scaling laws on nanoelectromechanical systems
We study the electromechanical transduction in nanoelectromechanical
actuators and show that the differences in scaling for electrical and
mechanical effects lead to an overall non-trivial scaling behavior. In
particular, the previously neglected fringing fields considerably increase
electrical forces and improve the stability of nanoscale actuators. This shows
that electrostatics does not pose any limitations to downscaling of
electromechanical systems, in fact in several respects, nanosystems outperform
their microscale counterparts. As a specific example, we consider in-plane
actuation of ultrathin slabs and show that devices consisting of a few layers
of graphene are feasible, implying that electromechanical resonators operating
beyond 40 GHz are possible with currently available technology
Stepwise Luneburg Lens for Bloch Surface Waves
In order to enlarge the capability for in-plane manipulation of the Bloch surface wave (BSW), we investigate 2D gradient index (GRIN) optical components using a finite-difference time-domain (FDTD) numerical method. To ease difficulties in fabrication to acquire a continuous index profile of GRIN optical components, we propose a stepwise index profile. For 2D surface wave devices, such discrete index steps can be achieved by stepwise structuring of the top layer, also called the device layer. For the demonstration of the stepwise GRIN optics concept, we consider a Luneburg lens, which is a good example of the GRIN optical component that produces a strong focal spot on the shadow-side curvature of the lens. The limited index contrast of the BSW systems loosens the confinement of the focal spot. A mitigation plan is to elongate the circular geometry to the prolate ellipse. BSW-based Luneburg lenses with a relatively small number of steps and an elliptical geometry are demonstrated with comparable performances to a standard Luneburg lens
Observation of strong backscattering in valley-Hall photonic topological interface modes
The unique properties of light underpin the visions of photonic quantum
technologies, optical interconnects, and a wide range of novel sensors, but a
key limiting factor today is losses due to either absorption or backscattering
on defects. Recent developments in topological photonics have fostered the
vision of backscattering-protected waveguides made from topological interface
modes, but, surprisingly, measurements of their propagation losses were so far
missing. Here we report on measurements of losses in the slow-light regime of
valley-Hall topological waveguides and find no indications of topological
protection against backscattering on ubiquitous structural defects. We image
the light scattered out from the topological waveguides and find that the
propagation losses are due to Anderson localization. Since valley-Hall photonic
topological interfaces are currently the only viable contenders for
backscattering-protected topological waveguides without absorption or
out-of-plane losses, our work raises fundamental questions about the real-world
value of topological protection in photonics
Optical surface waves on one-dimensional photonic crystals: investigation of loss mechanisms and demonstration of centimeter-scale propagation
It has been predicted that optical surface waves at interfaces that separate
purely dielectric media should be able to propagate over long distances,
particularly over distances greater than possible with surface plasmon
polaritons. Despite numerous studies, there has been no report of such an
observation, and an estimate of the propagation length achievable with
dielectric optical surface waves is yet to be provided. In this work, we focus
on the propagation properties of optical modes supported at the free surface of
a one-dimensional photonic crystal. The contributions of intrinsic and
extrinsic loss mechanisms are discussed. The developed understanding is applied
to the design of structures that are optimized to support long propagating
optical surface waves. We experimentally demonstrate, for the first time, the
existence of optical surface waves capable of propagating over centimeter-scale
distances in the visible spectral range. This result opens new perspectives for
the use of optical surface waves in integrated optics and for light-matter
interactions at interfaces.Comment: 11 pages, 4 figure
Inverse photonic design of functional elements that focus Bloch surface waves
Bloch surface waves (BSWs) are sustained at the interface of a suitably designed one-dimensional (1D) dielectric photonic crystal and an ambient material. The elements that control the propagation of BSWs are defined by a spatially structured device layer on top of the 1D photonic crystal that locally changes the effective index of the BSW. An example of such an element is a focusing device that squeezes an incident BSW into a tiny space. However, the ability to focus BSWs is limited since the index contrast achievable with the device layer is usually only on the order of Înâ0.1 for practical reasons. Conventional elements, e.g., discs or triangles, which rely on a photonic nanojet to focus BSWs, operate insufficiently at such a low index contrast. To solve this problem, we utilize an inverse photonic design strategy to attain functional elements that focus BSWs efficiently into spatial domains slightly smaller than half the wavelength. Selected examples of such functional elements are fabricated. Their ability to focus BSWs is experimentally verified by measuring the field distributions with a scanning near-field optical microscope. Our focusing elements are promising ingredients for a future generation of integrated photonic devices that rely on BSWs, e.g., to carry information, or lab-on-chip devices for specific sensing applications
A SAW Delay Line Sensor Combined with Micro-hotplate for Bio-chemical Applications
This paper presents a SAW delay line sensor for chemical and biological applications. The impulse response model is used for determination of IDT parameters and first order investigation. A three-dimensional finite element model of a SAW delay line on a silicon membrane with an AlN thin film is simulated. An additional micro-hotplate is combined with SAW system for thermal adjustment of sensing layer on required temperature and thermal stabilization for whole sensor. The designed SAW system works at 618 MHz with adequate wave confinement at the surface of the device. QUOTE S21 parameter and phase response of the sensor is calculated by applying an impulse signal to the sensor
Stepwise Luneburg Lens for Bloch Surface Waves
In order to enlarge the capability for in-plane manipulation of the Bloch surface wave (BSW), we investigate 2D gradient index (GRIN) optical components using a finite-difference time-domain (FDTD) numerical method. To ease difficulties in fabrication to acquire a continuous index profile of GRIN optical components, we propose a stepwise index profile. For 2D surface wave devices, such discrete index steps can be achieved by stepwise structuring of the top layer, also called the device layer. For the demonstration of the stepwise GRIN optics concept, we consider a Luneburg lens, which is a good example of the GRIN optical component that produces a strong focal spot on the shadow-side curvature of the lens. The limited index contrast of the BSW systems loosens the confinement of the focal spot. A mitigation plan is to elongate the circular geometry to the prolate ellipse. BSW-based Luneburg lenses with a relatively small number of steps and an elliptical geometry are demonstrated with comparable performances to a standard Luneburg lens
Investigation of the Propagation Length of Bloch Surface Waves on One Dimensional Photonic Crystals
A 1D photonic crystal structure sustaining optical surface waves is investigated. The propagation length of the surface mode is studied both using an eigenmode model and a rigorous time domain solver. The two models show good convergence. Our results demonstrate that by a carefully designed 1D photonic crystal, dielectric surface waves may propagate over several millimeters, even if a Kretschmann-type coupling configuration is used