349 research outputs found
Characterization of Power-to-Phase Conversion in High-Speed P-I-N Photodiodes
Fluctuations of the optical power incident on a photodiode can be converted
into phase fluctuations of the resulting electronic signal due to nonlinear
saturation in the semiconductor. This impacts overall timing stability (phase
noise) of microwave signals generated from a photodetected optical pulse train.
In this paper, we describe and utilize techniques to characterize this
conversion of amplitude noise to phase noise for several high-speed (>10 GHz)
InGaAs P-I-N photodiodes operated at 900 nm. We focus on the impact of this
effect on the photonic generation of low phase noise 10 GHz microwave signals
and show that a combination of low laser amplitude noise, appropriate
photodiode design, and optimum average photocurrent is required to achieve
phase noise at or below -100 dBc/Hz at 1 Hz offset a 10 GHz carrier. In some
photodiodes we find specific photocurrents where the power-to-phase conversion
factor is observed to go to zero
Soliton crystals in Kerr resonators
Strongly interacting solitons confined to an optical resonator would offer
unique capabilities for experiments in communication, computation, and sensing
with light. Here we report on the discovery of soliton crystals in monolithic
Kerr microresonators-spontaneously and collectively ordered ensembles of
co-propagating solitons whose interactions discretize their allowed temporal
separations. We unambiguously identify and characterize soliton crystals
through analysis of their 'fingerprint' optical spectra, which arise from
spectral interference between the solitons. We identify a rich space of soliton
crystals exhibiting crystallographic defects, and time-domain measurements
directly confirm our inference of their crystal structure. The crystallization
we observe is explained by long-range soliton interactions mediated by
resonator mode degeneracies, and we probe the qualitative difference between
soliton crystals and a soliton liquid that forms in the absence of these
interactions. Our work explores the rich physics of monolithic Kerr resonators
in a new regime of dense soliton occupation and offers a way to greatly
increase the efficiency of Kerr combs; further, the extreme degeneracy of the
configuration space of soliton crystals suggests an implementation for a robust
on-chip optical buffer
Fundamental noise limitations to supercontinuum generation in microstructure fiber
Broadband noise on supercontinuum spectra generated in microstructure fiber
is shown to lead to amplitude fluctuations as large as 50 % for certain input
laser pulse parameters. We study this noise using both experimental
measurements and numerical simulations with a generalized stochastic nonlinear
Schroedinger equation, finding good quantitative agreement over a range of
input pulse energies and chirp values. This noise is shown to arise from
nonlinear amplification of two quantum noise inputs: the input pulse shot noise
and the spontaneous Raman scattering down the fiber.Comment: 16 pages with 6 figure
Measurement of excited-state transitions in cold calcium atoms by direct femtosecond frequency-comb spectroscopy
We apply direct frequency-comb spectroscopy, in combination with precision cw
spectroscopy, to measure the transition
frequency in cold calcium atoms. A 657 nm ultrastable cw laser was used to
excite atoms on the narrow ( Hz) clock transition, and the direct output of the frequency comb was
used to excite those atoms from the state to the state. The resonance of this second stage was detected by observing a
decrease in population of the ground state as a result of atoms being optically
pumped to the metastable states. The transition frequency is measured to be kHz; which is an improvement by almost four orders of magnitude over
the previously measured value. In addition, we demonstrate spectroscopy on
magnetically trapped atoms in the state.Comment: 4 pages 5 figure
Ultra-precise measurement of optical frequency ratios
We developed a novel technique for frequency measurement and synthesis, based
on the operation of a femtosecond comb generator as transfer oscillator. The
technique can be used to measure frequency ratios of any optical signals
throughout the visible and near-infrared part of the spectrum. Relative
uncertainties of for averaging times of 100 s are possible. Using a
Nd:YAG laser in combination with a nonlinear crystal we measured the frequency
ratio of the second harmonic at 532 nm to the fundamental at
1064 nm, .Comment: 4 pages, 4 figure
Kilohertz-resolution spectroscopy of cold atoms with an optical frequency comb
We have performed sub-Doppler spectroscopy on the narrow intercombination
line of cold calcium atoms using the amplified output of a femtosecond laser
frequency comb. Injection locking of a 657-nm diode laser with a femtosecond
comb allows for two regimes of amplification, one in which many lines of the
comb are amplified, and one where a single line is predominantly amplified. The
output of the laser in both regimes was used to perform kilohertz-level
spectroscopy. This experiment demonstrates the potential for high-resolution
absolute-frequency spectroscopy over the entire spectrum of the frequency comb
output using a single high-finesse optical reference cavity.Comment: 4 pages, 4 Figure
Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider
We present an optical frequency divider based on a 200 MHz repetition rate
Er:fiber mode-locked laser that, when locked to a stable optical frequency
reference, generates microwave signals with absolute phase noise that is equal
to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz
carrier, the phase noise is below -100 dBc/Hz, limited by the optical
reference. For offset frequencies > 10 kHz, the phase noise is shot noise
limited at -145 dBc/Hz. An analysis of the contribution of the residual noise
from the Er:fiber optical frequency divider is also presented.Comment: 4 pages, 3 figure
Testing the stability of fundamental constants with the 199Hg+ single-ion optical clock
Over a two-year duration, we have compared the frequency of the 199Hg+ 5d106s
2S 1/2 (F=0) 5d9 6s2 2D 5/2 (F=2) electric-quadrupole transition at 282 nm
with the frequency of the ground-state hyperfine splitting in neutral 133Cs.
These measurements show that any fractional time variation of the ratio
nu(Cs)/nu(Hg) between the two frequencies is smaller than +/- 7 10^-15 / yr (1
sigma uncertainty). According to recent atomic structure calculations, this
sets an upper limit to a possible fractional time variation of g(Cs) m_e / m_p
alpha^6.0 at the same level.Comment: 4 pages with 3 figures. RevTeX 4, Submitted to Phys. Rev. Let
A Near Infrared Laser Frequency Comb for High Precision Doppler Planet Surveys
We discuss the laser frequency comb as a near infrared astronomical
wavelength reference, and describe progress towards a near infrared laser
frequency comb at the National Institute of Standards and Technology and at the
University of Colorado where we are operating a laser frequency comb suitable
for use with a high resolution H band astronomical spectrograph.Comment: 8 pages, 5 figures. Conference Proceedings, New Technologies for
Probing the Diversity of Brown Dwarfs and Exoplanets, Shanghai, China, 19-24
July, 2009. Submitted to Eur. Phys. J. Conference
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