50 research outputs found
Optical Frequency Comb Generation in Monolithic Microresonators
This thesis presents an entirely novel approach for frequency comb generation based on nonlinear frequency conversion in micrometer sized optical resonators. Here, the comb generation process can be directly described in frequency domain as energy conserving interactions between four photons (four-photon mixing). This process is a result of extremely high light intensities that build up in microresonators with long photon storage times. The thesis is composed of four main parts that answer fundamental questions in the context of microresonator-based frequency comb generation as well as providing insights in the control and possible applications of this type of comb generators
Hybrid Electro-Optically Modulated Microcombs
Optical frequency combs based on mode-locked lasers have proven to be
invaluable tools for a wide range of applications in precision spectroscopy and
metrology. A novel principle of optical frequency comb generation in
whispering-gallery mode microresonators ("microcombs") has been developed
recently, which represents a promising route towards chip-level integration and
out-of-the-lab use of these devices. Presently, two families of microcombs have
been demonstrated: combs with electronically detectable mode spacing that can
be directly stabilized, and broadband combs with up to octave-spanning spectra
but mode spacings beyond electronic detection limits. However, it has not yet
been possible to achieve these two key requirements simultaneously, as will be
critical for most microcomb applications. Here we present a key step to
overcome this problem by interleaving an electro-optic comb with the spectrum
from a parametric microcomb. This allows, for the first time, direct control
and stabilization of a microcomb spectrum with large mode spacing (>140 GHz)
with no need for an additional mode-locked laser frequency comb. The attained
residual 1-second-instability of the microcomb comb spacing is 10^-15, with a
microwave reference limited absolute instability of 10^-12 at a 140 GHz mode
spacing.Comment: 8 pages, 4 figures; accepted for publication in Physical Review
Letter
Parametric seeding of a microresonator optical frequency comb
We have investigated parametric seeding of a microresonator frequency comb
(microcomb) by way of a pump laser with two electro-optic-modulation sidebands.
We show that the pump-sideband spacing is precisely replicated throughout the
microcomb's optical spectrum, and we demonstrate a record absolute line-spacing
stability for microcombs of at 1 s. The spectrum of a
parametric comb is complex, and often non-equidistant subcombs are observed.
Our results demonstrate that parametric seeding can not only control the
subcombs, but can lead to the generation of a strictly equidistant microcomb
spectrum.Comment: 10 pages, 5 figure
Microresonator Soliton Frequency Combs in the Zero-Dispersion Regime
Chip-scale optical frequency combs have attracted significant research
interest and can be used in applications ranging from precision spectroscopy to
telecom channel generators and lidar systems. In the time domain,
microresonator based frequency combs correspond to self-stabilized soliton
pulses. In two distinct regimes, microresonators have shown to emit either
bright solitons in the anomalous dispersion regime or dark solitons (a short
time of darkness in a bright background signal) in the normal dispersion
regime. Here, we investigate the dynamics of continuous-wave-laser-driven
soliton generation in the zero-group-velocity-dispersion (GVD) regime, as well
as the generation of solitons that are spectrally crossing different dispersion
regimes. In the measurements we observe zero-dispersion solitons with doublet
structures (soliton molecules) that can be deterministically accessed with a
predictable spectral envelope. Numerical simulations agree well with the
observed soliton structures. These results could be of interest for chip-based
pump-probe schemes, optical telecom systems, gas sensing and precision
metrology
Self-synchronization of Kerr-nonlinear Optical Parametric Oscillators
We introduce a new, reduced nonlinear oscillator model governing the
spontaneous creation of sharp pulses in a damped, driven, cubic nonlinear
Schroedinger equation. The reduced model embodies the fundamental connection
between mode synchronization and spatiotemporal pulse formation. We identify
attracting solutions corresponding to stable cavity solitons and Turing
patterns. Viewed in the optical context, our results explain the recently
reported and steps in the phase spectrum of microresonator-based
optical frequency combs
Self-synchronization Phenomena in the Lugiato-Lefever Equation
The damped driven nonlinear Schr\"odinger equation (NLSE) has been used to
understand a range of physical phenomena in diverse systems. Studying this
equation in the context of optical hyper-parametric oscillators in
anomalous-dispersion dissipative cavities, where NLSE is usually referred to as
the Lugiato-Lefever equation (LLE), we are led to a new, reduced nonlinear
oscillator model which uncovers the essence of the spontaneous creation of
sharply peaked pulses in optical resonators. We identify attracting solutions
for this model which correspond to stable cavity solitons and Turing patterns,
and study their degree of stability. The reduced model embodies the fundamental
connection between mode synchronization and spatiotemporal pattern formation,
and represents a novel class of self-synchronization processes in which
coupling between nonlinear oscillators is governed by energy and momentum
conservation.Comment: This manuscript is published in Physical Review A. Copyright 2017 by
the American Physical Society. arXiv admin note: text overlap with
arXiv:1602.0852
Optical memories and switching dynamics of counterpropagating light states in microresonators
The Kerr nonlinearity can be a key enabler for many digital photonic circuits
as it allows access to bistable states needed for all-optical memories and
switches. A common technique is to use the Kerr shift to control the resonance
frequency of a resonator and use it as a bistable, optically-tunable filter.
However, this approach works only in a narrow power and frequency range or
requires the use of an auxiliary laser. An alternative approach is to use the
asymmetric bistability between counterpropagating light states resulting from
the interplay between self- and cross-phase modulation, which allows light to
enter a ring resonator in just one direction. Logical HIGH and LOW states can
be represented and stored as the direction of circulation of light, and
controlled by modulating the input power. Here we study the switching speed,
operating laser frequency and power range, and contrast ratio of such a device.
We reach a bitrate of 2 Mbps in our proof-of-principle device over an optical
frequency range of 1 GHz and an operating power range covering more than one
order of magnitude. We also calculate that integrated photonic circuits could
exhibit bitrates of the order of Gbps, paving the way for the realization of
robust and simple all-optical memories, switches, routers and logic gates that
can operate at a single laser frequency with no additional electrical power.Comment: 10 pages, 10 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