592 research outputs found
Optical microsphere resonators: optimal coupling to high-Q whispering gallery modes
A general model is presented for coupling of high- whispering-gallery
modes in optical microsphere resonators with coupler devices possessing
discrete and continuous spectrum of propagating modes. By contrast to
conventional high-Q optical cavities, in microspheres independence of high
intrinsic quality-factor and controllable parameters of coupling via evanescent
field offer variety of regimes earlier available in RF devices. The theory is
applied to the earlier-reported data on different types of couplers to
microsphere resonators and complemented by experimental demonstration of
enhanced coupling efficiency (about 80%) and variable loading regimes with
Q>10^8 fused silica microspheres.Comment: 14 pages, 4 figure
Mid-Infrared ultra-high-Q resonators based on fluoride crystalline materials
Decades ago, the losses of glasses in the near infrared (near-IR) were
investigated in views of developments for optical telecommunications. Today,
properties in the mid-infrared (mid-IR) are of interest for molecular
spectroscopy applications. In particular, high-sensitivity spectroscopic
techniques based on high-finesse mid-IR cavities hold high promise for medical
applications. Due to exceptional purity and low losses, whispering gallery mode
microresonators based on polished alkaline earth metal fluoride crystals (i.e
the family, where X Ca, Mg, Ba, Sr,...) have attained
ultra-high quality (Q) factor resonances (Q10) in the near-IR and
visible spectral ranges. Here we report for the first time ultra-high Q factors
in the mid-IR using crystalline microresonators. Using an uncoated chalcogenide
(ChG) tapered fiber, light from a continuous wave quantum cascade laser (QCL)
is efficiently coupled to several crystalline microresonators at 4.4 m
wavelength. We measure the optical Q factor of fluoride crystals in the mid-IR
using cavity ringdown technique. We observe that
microresonators feature quality factors that are very close to the fundamental
absorption limit, as caused by the crystal's multiphonon absorption
(Q10), in contrast to near-IR measurements far away from these
fundamental limits. Due to lower multiphonon absorption in and
, we show that ultra-high quality factors of Q 1.4
can be reached at 4.4 m. This corresponds to an optical
finesse of 4 10, the highest value achieved for any
type of mid-IR resonator to date, and a more than 10-fold improvement over the
state-of-the-art. Such compact ultra-high Q crystalline microresonators provide
a route for narrow linewidth frequency-stabilized QCL or mid-IR Kerr comb
generation.Comment: C. Lecaplain and C. Javerzac-Galy contributed equally to this wor
Frequency combs and platicons in optical microresonators with normal GVD
We predict the existence of a novel type of the flat-top dissipative
solitonic pulses, "platicons", in microresonators with normal group velocity
dispersion (GVD). We propose methods to generate these platicons from cw pump.
Their duration may be altered significantly by tuning the pump frequency. The
transformation of a discrete energy spectrum of dark solitons of the
Lugiato-Lefever equation into a quasicontinuous spectrum of platicons is
demonstrated. Generation of similar structures is also possible with
bi-harmonic, phase/amplitude modulated pump or via laser injection locking.Comment: 9 pages, 6 figure
Octave Spanning Frequency Comb on a Chip
Optical frequency combs have revolutionized the field of frequency metrology
within the last decade and have become enabling tools for atomic clocks, gas
sensing and astrophysical spectrometer calibration. The rapidly increasing
number of applications has heightened interest in more compact comb generators.
Optical microresonator based comb generators bear promise in this regard.
Critical to their future use as 'frequency markers', is however the absolute
frequency stabilization of the optical comb spectrum. A powerful technique for
this stabilization is self-referencing, which requires a spectrum that spans a
full octave, i.e. a factor of two in frequency. In the case of mode locked
lasers, overcoming the limited bandwidth has become possible only with the
advent of photonic crystal fibres for supercontinuum generation. Here, we
report for the first time the generation of an octave-spanning frequency comb
directly from a toroidal microresonator on a silicon chip. The comb spectrum
covers the wavelength range from 990 nm to 2170 nm and is retrieved from a
continuous wave laser interacting with the modes of an ultra high Q
microresonator, without relying on external broadening. Full tunability of the
generated frequency comb over a bandwidth exceeding an entire free spectral
range is demonstrated. This allows positioning of a frequency comb mode to any
desired frequency within the comb bandwidth. The ability to derive octave
spanning spectra from microresonator comb generators represents a key step
towards achieving a radio-frequency to optical link on a chip, which could
unify the fields of metrology with micro- and nano-photonics and enable
entirely new devices that bring frequency metrology into a chip scale setting
for compact applications such as space based optical clocks
Synthesis and Properties of Dipyridylcyclopentenes
A short and general route to the substituted dipyridylcyclopentenes was explored and several new compounds belonging to this new group of diarylethenes were synthesized. The study of their photochromic and thermochromic properties shows that the rate of the thermal ring opening is strongly dependent on the polarity of the solvent.
Mode spectrum and temporal soliton formation in optical microresonators
The formation of temporal dissipative solitons in optical microresonators
enables compact, high repetition rate sources of ultra-short pulses as well as
low noise, broadband optical frequency combs with smooth spectral envelopes.
Here we study the influence of the resonator mode spectrum on temporal soliton
formation. Using frequency comb assisted diode laser spectroscopy, the measured
mode structure of crystalline MgF2 resonators are correlated with temporal
soliton formation. While an overal general anomalous dispersion is required, it
is found that higher order dispersion can be tolerated as long as it does not
dominate the resonator's mode structure. Mode coupling induced avoided
crossings in the resonator mode spectrum are found to prevent soliton
formation, when affecting resonator modes close to the pump laser. The
experimental observations are in excellent agreement with numerical simulations
based on the nonlinear coupled mode equations, which reveal the rich interplay
of mode crossings and soliton formation
Temporal solitons in optical microresonators
Dissipative solitons can emerge in a wide variety of dissipative nonlinear
systems throughout the fields of optics, medicine or biology. Dissipative
solitons can also exist in Kerr-nonlinear optical resonators and rely on the
double balance between parametric gain and resonator loss on the one hand and
nonlinearity and diffraction or dispersion on the other hand. Mathematically
these solitons are solution to the Lugiato-Lefever equation and exist on top of
a continuous wave (cw) background. Here we report the observation of temporal
dissipative solitons in a high-Q optical microresonator. The solitons are
spontaneously generated when the pump laser is tuned through the effective zero
detuning point of a high-Q resonance, leading to an effective red-detuned
pumping. Red-detuned pumping marks a fundamentally new operating regime in
nonlinear microresonators. While usually unstablethis regime acquires unique
stability in the presence of solitons without any active feedback on the
system. The number of solitons in the resonator can be controlled via the pump
laser detuning and transitions to and between soliton states are associated
with discontinuous steps in the resonator transmission. Beyond enabling to
study soliton physics such as soliton crystals our observations open the route
towards compact, high repetition-rate femto-second sources, where the operating
wavelength is not bound to the availability of broadband laser gain media. The
single soliton states correspond in the frequency domain to low-noise optical
frequency combs with smooth spectral envelopes, critical to applications in
broadband spectroscopy, telecommunications, astronomy and low phase-noise
microwave generation.Comment: Includes Supplementary Informatio
- …