38 research outputs found
Dielectric tuning and coupling of whispering gallery modes using an anisotropic prism
Optical whispering gallery mode (WGM) resonators are a powerful and versatile
tool used in many branches of science. Fine tuning of the central frequency and
line width of individual resonances is however desirable in a number of
applications including frequency conversion, optical communications and
efficient light-matter coupling. To this end we present a detailed theoretical
analysis of dielectric tuning of WGMs supported in axisymmetric resonators.
Using the Bethe-Schwinger equation and adopting an angular spectrum field
representation we study the resonance shift and mode broadening of high
WGMs when a planar dielectric substrate is brought close to the resonator.
Particular focus is given to use of a uniaxial substrate with an arbitrarily
aligned optic axis. Competing red and blue resonance shifts ( MHz),
deriving from generation of a near field material polarisation and back action
from the radiation continuum respectively, are found. Anomalous resonance
shifts can hence be observed depending on the substrate material, whereas mode
broadening on the order of MHz can also be simply realised.
Furthermore, polarisation selective coupling with extinction ratios of
can be achieved when the resonator and substrate are of the same composition
and their optic axes are chosen correctly. Double refraction and properties of
out-coupled beams are also discussed
Resonant Electro-Optic Frequency Comb
High speed optical telecommunication is enabled by wavelength division
multiplexing, whereby hundreds of individually stabilized lasers encode the
information within a single mode optical fiber. In the seek for larger
bandwidth the optical power sent into the fiber is limited by optical
non-linearities within the fiber and energy consumption of the light sources
starts to become a significant cost factor. Optical frequency combs have been
suggested to remedy this problem by generating multiple laser lines within a
monolithic device, their current stability and coherence lets them operate only
in small parameter ranges. Here we show that a broadband frequency comb
realized through the electro-optic effect within a high quality whispering
gallery mode resonator can operate at low microwave and optical powers.
Contrary to the usual third order Kerr non-linear optical frequency combs we
rely on the second order non-linear effect which is much more efficient. Our
result uses a fixed microwave signal which is mixed with an optical pump signal
to generate a coherent frequency comb with a precisely determined carrier
separation. The resonant enhancement enables us to operate with microwave
powers three order magnitude smaller than in commercially available devices. We
can expect the implementation into the next generation long distance
telecommunication which relies on coherent emission and detection schemes to
allow for operation with higher optical powers and at reduced cost
Experimental characterization of an uniaxial angle cut whispering gallery mode resonator
The usual configuration of uniaxial whispering gallery mode resonators is a
disk shaped geometry where the optic axis points along the symmetry axis, a so
called z-cut resonator. Recently x-cut resonators, where the optic axis lies in
the equatorial plane, became of interest as they enable extremely broadband
second harmonic generation. In this paper we report on the properties of a more
generalized system, the so called angle-cut resonator, where the optic axis
exhibits an arbitrary angle against the symmetry axis. We show experimentally
that the modal structure and quality factors are similar to common resonators
but that the polarization properties differ quite significantly: due to the
asymmetry the polarization depends on the equatorial position and is, in
general, elliptical
Coherent conversion between microwave and optical photons -- an overview of physical implementations
Quantum information technology based on solid state qubits has created much
interest in converting quantum states from the microwave to the optical domain.
Optical photons, unlike microwave photons, can be transmitted by fiber, making
them suitable for long distance quantum communication. Moreover, the optical
domain offers access to a large set of very well developed quantum optical
tools, such as highly efficient single-photon detectors and long-lived quantum
memories. For a high fidelity microwave to optical transducer, efficient
conversion at single photon level and low added noise is needed. Currently, the
most promising approaches to build such systems are based on second order
nonlinear phenomena such as optomechanical and electro-optic interactions.
Alternative approaches, although not yet as efficient, include magneto-optical
coupling and schemes based on isolated quantum systems like atoms, ions or
quantum dots. In this Progress Report, we provide the necessary theoretical
foundations for the most important microwave-to-optical conversion experiments,
describe their implementations and discuss current limitations and future
prospects.Comment: 17 Pages, 8 Figure
Frequency tuning of a triply-resonant whispering-gallery mode resonator to MHz wide transitions for proposed quantum repeater schemes
Quantum repeaters rely on an interfacing of flying qubits with quantum
memories. The most common implementations include a narrowband single photon
matched in bandwidth and central frequency to an atomic system. Previously, we
demonstrated the compatibility of our versatile source of heralded single
photons, which is based on parametric down-conversion in a triply-resonant
whispering-gallery mode resonator, with alkaline transitions [Schunk et al.,
Optica 2, 773 (2015)]. In this paper, we analyze our source in terms of phase
matching, available wavelength-tuning mechanisms, and applications to
narrow-band atomic systems. We resonantly address the D1 transitions of cesium
and rubidium with this optical parametric oscillator pumped above its
oscillation threshold. Below threshold, the efficient coupling of single
photons to atomic transitions heralded by single telecom-band photons is
demonstrated. Finally, we present an accurate analytical description of our
observations. Providing the demonstrated flexibility in connecting various
atomic transitions with telecom wavelengths, we show a promising approach to
realize an essential building block for quantum repeaters.Comment: 18 pages, 14 figure
Interfacing transitions of different alkali atoms and telecom bands using one narrowband photon pair source
Quantum information technology strongly relies on coupling of optical photons
with narrowband quantum systems, such as quantum dots, color centers, and
atomic systems. This coupling requires matching the optical wavelength and
bandwidth to the desired system, which presents a considerable problem for most
available sources of quantum light. Here we demonstrate coupling of alkali
dipole transitions with a tunable source of photon pairs. Our source is based
on spontaneous parametric down-conversion in a triply-resonant
whispering-gallery mode resonator. For this, we have developed novel wavelength
tuning mechanisms, which allow for a coarse tuning to either cesium or rubidium
wavelength with subsequent continuous fine-tuning to the desired transition. As
a demonstration of the functionality of the source, we performed a heralded
single photon measurement of the atomic decay. We present a major advance in
controlling the spontaneous down-conversion process, which makes our bright
source of single photons now compatible with a plethora of narrow-band resonant
systems.Comment: 8 pages, 5 figure
Revealing the Landscape of Privacy-Enhancing Technologies in the Context of Data Markets for the IoT: A Systematic Literature Review
IoT data markets in public and private institutions have become increasingly
relevant in recent years because of their potential to improve data
availability and unlock new business models. However, exchanging data in
markets bears considerable challenges related to disclosing sensitive
information. Despite considerable research focused on different aspects of
privacy-enhancing data markets for the IoT, none of the solutions proposed so
far seems to find a practical adoption. Thus, this study aims to organize the
state-of-the-art solutions, analyze and scope the technologies that have been
suggested in this context, and structure the remaining challenges to determine
areas where future research is required. To accomplish this goal, we conducted
a systematic literature review on privacy enhancement in data markets for the
IoT, covering 50 publications dated up to July 2020, and provided updates with
24 publications dated up to May 2022. Our results indicate that most research
in this area has emerged only recently, and no IoT data market architecture has
established itself as canonical. Existing solutions frequently lack the
required combination of anonymization and secure computation technologies.
Furthermore, there is no consensus on the appropriate use of blockchain
technology for IoT data markets and a low degree of leveraging existing
libraries or reusing generic data market architectures. We also identified
significant challenges remaining, such as the copy problem and the recursive
enforcement problem that-while solutions have been suggested to some extent-are
often not sufficiently addressed in proposed designs. We conclude that
privacy-enhancing technologies need further improvements to positively impact
data markets so that, ultimately, the value of data is preserved through data
scarcity and users' privacy and businesses-critical information are protected.Comment: 49 pages, 17 figures, 11 table
Squeezed vacuum states from a whispering gallery mode resonator
Squeezed vacuum states enable optical measurements below the quantum limit
and hence are a valuable resource for applications in quantum metrology and
also quantum communication. However, most available sources require high pump
powers in the milliwatt range and large setups, which hinders real world
applications. Furthermore, degenerate operation of such systems presents a
challenge. Here, we use a compact crystalline whispering gallery mode resonator
made of lithium niobate as a degenerate parametric oscillator. We demonstrate
about 1.4 dB noise reduction below the shot noise level for only 300
of pump power in degenerate single mode operation. Furthermore,
we report a record pump threshold as low as 1.35 . Our results
show that the whispering gallery based approach presents a promising platform
for a compact and efficient source for nonclassical light.Comment: 2019 Optical Society of America. Users may use, reuse,
and build upon the article, or use the article for text or data mining, so
long as such uses are for non-commercial purposes and appropriate attribution
is maintained. All other rights are reserve
Nonlinear power dependence of the spectral properties of an optical parametric oscillator below threshold in the quantum regime
Photon pairs and heralded single photons, obtained from cavity-assisted
parametric down-conversion (PDC), play an important role in quantum
communications and technology. This motivated a thorough study of the spectral
and temporal properties of parametric light, both above the Optical Parametric
Oscillator (OPO) threshold, where the semiclassical approach is justified, and
deeply below it, where the linear cavity approximation is applicable. The
pursuit of a higher two-photon emission rate leads into an interesting
intermediate regime where the OPO still operates considerably below the
threshold but the nonlinear cavity phenomena cannot be neglected anymore. Here,
we investigate this intermediate regime and show that the spectral and temporal
properties of the photon pairs, as well as their emission rate, may
significantly differ from the widely accepted linear model. The observed
phenomena include frequency pulling and broadening in the temporal correlation
for the down-converted optical fields. These factors need to be taken into
account when devising practical applications of the high-rate cavity-assisted
SPDC sources
Revealing the landscape of privacy-enhancing technologies in the context of data markets for the IoT: A systematic literature review
IoT data markets in public and private institutions have become increasingly relevant in recent years because of their potential to improve data availability and unlock new business models. However, exchanging data in markets bears considerable challenges related to disclosing sensitive information. Despite considerable research focused on different aspects of privacy-enhancing data markets for the IoT, none of the solutions proposed so far seems to find a practical adoption. Thus, this study aims to organize the state-of-the-art solutions, analyze and scope the technologies that have been suggested in this context, and structure the remaining challenges to determine areas where future research is required. To accomplish this goal, we conducted a systematic literature review on privacy enhancement in data markets for the IoT, covering 50 publications dated up to July 2020, and provided updates with 24 publications dated up to May 2022. Our results indicate that most research in this area has emerged only recently, and no IoT data market architecture has established itself as canonical. Existing solutions frequently lack the required combination of anonymization and secure computation technologies. Furthermore, there is no consensus on the appropriate use of blockchain technology for IoT data markets and a low degree of leveraging existing libraries or reusing generic data market architectures. We also identified significant challenges remaining, such as the copy problem and the recursive enforcement problem that - while solutions have been suggested to some extent - are often not sufficiently addressed in proposed designs. We conclude that privacy-enhancing technologies need further improvements to positively impact data markets so that, ultimately, the value of data is preserved through data scarcity and users' privacy and businesses-critical information are protected