52 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
Nonlinear and Quantum Optics with Whispering Gallery Resonators
Optical Whispering Gallery Modes (WGMs) derive their name from a famous
acoustic phenomenon of guiding a wave by a curved boundary observed nearly a
century ago. This phenomenon has a rather general nature, equally applicable to
sound and all other waves. It enables resonators of unique properties
attractive both in science and engineering. Very high quality factors of
optical WGM resonators persisting in a wide wavelength range spanning from
radio frequencies to ultraviolet light, their small mode volume, and tunable
in- and out- coupling make them exceptionally efficient for nonlinear optical
applications. Nonlinear optics facilitates interaction of photons with each
other and with other physical systems, and is of prime importance in quantum
optics. In this paper we review numerous applications of WGM resonators in
nonlinear and quantum optics. We outline the current areas of interest,
summarize progress, highlight difficulties, and discuss possible future
development trends in these areas.Comment: This is a review paper with 615 references, submitted to J. Op
Gallium arsenide whispering gallery mode resonators for terahertz photonics
As the field of terahertz (THz) photonics advances, we present a monolithic
gallium arsenide (GaAs) disk-shaped whispering gallery mode resonator that has
potential as a component in THz nonlinear optics. GaAs is a material with
significant optical nonlinearity which can be enhanced when the crystal is
shaped into a microdisk resonator. A 4-mm-disk-resonator was fabricated using
single-point diamond turning and was characterised to obtain a quality (Q)
factor of 2.2k at ~150 GHz and 1.4k at ~300 GHz. We also demonstrated the
blue-shifting of up to ~0.3 GHz of the THz modes using a block of metal. This
post-fabrication degree of freedom could be useful for phase-matching
requirements for nonlinear optical processes, such as detection based on
optical up-conversion of THz radiation. Such a compact, tunable and efficient
device could be integrated into nonlinear photonic platforms for THz
generation, manipulation and detection.Comment: 8 pages, 5 figure
Polarization properties and dispersion relations for spiral resonances of a dielectric rod
Dielectric microcavities based on cylindrical and deformed cylindrical shapes
have been employed as resonators for microlasers. Such systems support spiral
resonances with finite momentum along the cylinder axis. For such modes the
boundary conditions do not separate and simple TM and TE polarization states do
not exist. We formulate a theory for the dispersion relations and polarization
properties of such resonances for an infinite dielectric rod of arbitrary
cross-section and then solve for these quantities for the case of a circular
cross-section (cylinder). Useful analytic formulas are obtained using the
eikonal (Einstein-Brillouin-Keller) method which are shown to be excellent
approximations to the exact results from the wave equation. The major finding
is that the polarization of the radiation emitted into the far-field is linear
up to a polarization critical angle (PCA) at which it changes to elliptical.
The PCA always lies between the Brewster and total-internal-reflection angles
for the dielectric, as is shown by an analysis based on the Jones matrices of
the spiraling rays.Comment: submitted to JOSA
Finite element simulation of a perturbed axial-symmetric whispering-gallery mode and its use for intensity enhancement with a nanoparticle coupled to a microtoroid
We present an optical mode solver for a whispering gallery resonator coupled
to an adjacent arbitrary shaped nano-particle that breaks the axial symmetry of
the resonator. Such a hybrid resonator-nanoparticle is similar to what was
recently used for bio-detection and for field enhancement. We demonstrate our
solver by parametrically studying a toroid-nanoplasmonic device and get the
optimal nano-plasmonic size for maximal enhancement. We investigate cases near
a plasmonic resonance as well as far from a plasmonic resonance. Unlike common
plasmons that typically benefit from working near their resonance, here working
far from plasmonic resonance provides comparable performance. This is because
the plasmonic resonance enhancement is accompanied by cavity quality
degradation through plasmonic absorption.Comment: Supplementary COMSOL script, see
http://www.quantumchaos.de/Media/comsol2013/Supplement_Script_for_Fig.3_Comsol_4.3a.mp
Static Envelope Patterns in Composite Resonances Generated by Level Crossing in Optical Toroidal Microcavities
We study level crossing in the optical whispering-gallery (WG) modes by using toroidal microcavities. Experimentally, we image the stationary envelope patterns of the composite optical modes that arise when WG modes of different wavelengths coincide in frequency. Numerically, we calculate crossings of levels that correspond with the observed degenerate modes, where our method takes into account the not perfectly transverse nature of their field polarizations. In addition, we analyze anticrossing with a large avoidance gap between modes of the same azimuthal number
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