111 research outputs found
General Relativistic Contributions in Transformation Optics
One potentially realistic specification for devices designed with
transformation optics is that they operate with high precision in curved
space-time, such as Earth orbit. This raises the question of what, if any, role
does space-time curvature play in determining transformation media?
Transformation optics has been based on a three-vector representation of
Maxwell's equations in flat Minkowski space-time. I discuss a completely
covariant, manifestly four-dimensional approach that enables transformations in
arbitrary space-times, and demonstrate this approach for stable circular orbits
in the spherically symmetric Schwarzschild geometry. Finally, I estimate the
magnitude of curvature induced contributions to satellite-borne transformation
media in Earth orbit and comment on the level of precision required for
metamaterial fabrication before such contributions become important.Comment: 14 pages, 3 figures. Latest version has expanded analysis,
corresponds to published versio
Octave-spanning frequency comb generation in a silicon nitride chip
We demonstrate a frequency comb spanning an octave via the parametric process
of cascaded four-wave mixing in a monolithic, high-Q silicon nitride microring
resonator. The comb is generated from a single-frequency pump laser at 1562 nm
and spans 128 THz with a spacing of 226 GHz, which can be tuned slightly with
the pump power. In addition, we investigate the RF-noise characteristics of the
parametric comb and find that the comb can operate in a low-noise state with a
30-dB reduction in noise as the pump frequency is tuned into the cavity
resonance
Spectral Line-by-Line Pulse Shaping of an On-Chip Microresonator Frequency Comb
We report, for the first time to the best of our knowledge, spectral phase
characterization and line-by-line pulse shaping of an optical frequency comb
generated by nonlinear wave mixing in a microring resonator. Through
programmable pulse shaping the comb is compressed into a train of
near-transform-limited pulses of \approx 300 fs duration (intensity full width
half maximum) at 595 GHz repetition rate. An additional, simple example of
optical arbitrary waveform generation is presented. The ability to characterize
and then stably compress the frequency comb provides new data on the stability
of the spectral phase and suggests that random relative frequency shifts due to
uncorrelated variations of frequency dependent phase are at or below the 100
microHertz level.Comment: 18 pages, 4 figure
An Integrated-Photonics Optical-Frequency Synthesizer
Integrated-photonics microchips now enable a range of advanced
functionalities for high-coherence applications such as data transmission,
highly optimized physical sensors, and harnessing quantum states, but with
cost, efficiency, and portability much beyond tabletop experiments. Through
high-volume semiconductor processing built around advanced materials there
exists an opportunity for integrated devices to impact applications cutting
across disciplines of basic science and technology. Here we show how to
synthesize the absolute frequency of a lightwave signal, using integrated
photonics to implement lasers, system interconnects, and nonlinear frequency
comb generation. The laser frequency output of our synthesizer is programmed by
a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and
traceability to the SI second. This is accomplished with a heterogeneously
integrated III/V-Si tunable laser, which is guided by dual
dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through
out-of-loop measurements of the phase-coherent, microwave-to-optical link, we
verify that the fractional-frequency instability of the integrated photonics
synthesizer matches the reference-clock instability for a 1
second acquisition, and constrain any synthesis error to while
stepping the synthesizer across the telecommunication C band. Any application
of an optical frequency source would be enabled by the precision optical
synthesis presented here. Building on the ubiquitous capability in the
microwave domain, our results demonstrate a first path to synthesis with
integrated photonics, leveraging low-cost, low-power, and compact features that
will be critical for its widespread use.Comment: 10 pages, 6 figure
Performance analysis of polling systems with retrials and glue periods
We consider gated polling systems with two special features: (i) retrials,
and (ii) glue or reservation periods. When a type- customer arrives, or
retries, during a glue period of station , it will be served in the next
visit period of the server to that station. Customers arriving at station
in any other period join the orbit of that station and retry after an
exponentially distributed time. Such polling systems can be used to study the
performance of certain switches in optical communication systems.
For the case of exponentially distributed glue periods, we present an
algorithm to obtain the moments of the number of customers in each station. For
generally distributed glue periods, we consider the distribution of the total
workload in the system, using it to derive a pseudo conservation law which in
its turn is used to obtain accurate approximations of the individual mean
waiting times. We also consider the problem of choosing the lengths of the glue
periods, under a constraint on the total glue period per cycle, so as to
minimize a weighted sum of the mean waiting times
Dual-pump Kerr micro-cavity optical frequency comb with varying FSR spacing
In this paper, we demonstrate a novel dual-pump approach to generate robust optical frequency comb with varying free spectral range (FSR) spacing in a CMOS-compatible high-Q micro-ring resonator (MRR). The frequency spacing of the comb can be tuned by an integer number FSR of the MRR freely in our dual-pump scheme. The dual pumps are self-oscillated in the laser cavity loop and their wavelengths can be tuned flexibly by programming the tunable filter embedded in the cavity. By tuning the pump wavelength, broadband OFC with the bandwidth of >180nm and the frequency-spacing varying from 6 to 46-fold FSRs is realized at a low pump power. This approach could find potential and practical applications in many areas, such as optical metrology, optical communication, and signal processing systems, for its excellent flexibility and robustness
Performance investigation of microphotonic-silicon devices in a field-trial all-optical network
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The performance of microphotonic-silicon devices in a geographically-distributed optical fiber network is experimentally investigated. Two different devices are tested: an optical filter based on a silicon ring resonator and an all-optical wavelength converter based on four-wave mixing in a dispersion-tailored highly nonlinear silicon waveguide. The evaluation of the devices is performed by means of eye diagrams and measurements of the bit error rate. (C) 2008 Elsevier B.V. All rights reserved.2825849855Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2006/52952-1, 2006/50911-6, 2005/51689-2]CNPq [305992/2005-8
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