66 research outputs found
Avoiding Aliasing in Allan Variance: an Application to Fiber Link Data Analysis
Optical fiber links are known as the most performing tools to transfer
ultrastable frequency reference signals. However, these signals are affected by
phase noise up to bandwidths of several kilohertz and a careful data processing
strategy is required to properly estimate the uncertainty. This aspect is often
overlooked and a number of approaches have been proposed to implicitly deal
with it. Here, we face this issue in terms of aliasing and show how typical
tools of signal analysis can be adapted to the evaluation of optical fiber
links performance. In this way, it is possible to use the Allan variance as
estimator of stability and there is no need to introduce other estimators. The
general rules we derive can be extended to all optical links. As an example, we
apply this method to the experimental data we obtained on a 1284 km coherent
optical link for frequency dissemination, which we realized in Italy
Distributed Raman optical amplification in phase coherent transfer of optical frequencies
We describe the application of Raman Optical-fiber Amplification (ROA) for
the phase coherent transfer of optical frequencies in an optical fiber link.
ROA uses the transmission fiber itself as a gain medium for bi-directional
coherent amplification. In a test setup we evaluated the ROA in terms of on-off
gain, signal-to-noise ratio, and phase noise added to the carrier. We
transferred a laser frequency in a 200 km optical fiber link with an additional
16 dB fixed attenuator (equivalent to 275 km of fiber on a single span), and
evaluated both co-propagating and counter-propagating amplification pump
schemes, demonstrating nonlinear effects limiting the co-propagating pump
configuration. The frequency at the remote end has a fractional frequency
instability of 3e-19 over 1000 s with the optical fiber link noise
compensation
Spectral purity transfer with 5 Ć 10ā17 instability at 1 s using a multibranch Er:fiber frequency comb
In this work we describe the spectral purity transfer between a 1156 nm ultrastable laser and a
1542 nm diode laser by means of an Er:fiber multibranch comb. By using both the master laser
light at 1156 nm and its second-harmonic at 578 nm, together with the 1542 nm slave laser,
we investigate the residual noise between the main comb output, the octave-spanning output,
and a wavelength conversion module including non-linear fibers, second-harmonic generation
crystal and amplifiers. With an ultimate stability of the system at the level of 5Eā17 at 1 s
and accuracy of 3Eā19, this configuration can sustain spectral transfer at the level required
by the contemporary optical clocks with a simple and robust setup
Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network
We performed a two-way remote optical phase comparison on optical fiber. Two
optical frequency signals were launched in opposite directions in an optical
fiber and their phases were simultaneously measured at the other end. In this
technique, the fiber noise was passively cancelled, and we compared two optical
frequencies at the ultimate 1E-21 stability level. The experiment was performed
on a 47 km fiber that is part of the metropolitan network for Internet traffic.
The technique relies on the synchronous measurement of the optical phases at
the two ends of the link, that is made possible by the use of digital
electronics. This scheme offers several advantages with respect to active noise
cancellation, and can be upgraded to perform more complex tasks
Absolute frequency measurement of the 1S0 - 3P0 transition of 171Yb
We report the absolute frequency measurement of the unperturbed transition
1S0 - 3P0 at 578 nm in 171Yb realized in an optical lattice frequency standard.
The absolute frequency is measured 518 295 836 590 863.55(28) Hz relative to a
cryogenic caesium fountain with a fractional uncertainty of 5.4x10-16 . This
value is in agreement with the ytterbium frequency recommended as a secondary
representation of the second in the International System of Units.Comment: This is an author-created, un-copyedited version of an article
accepted for publication/published in Metrologia. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The Version of Record is available online at
http://dx.doi.org/10.1088/1681-7575/aa4e62. It is published under a CC BY
licenc
LinkO: un'infrastruttura in fibra ottica per confronti remoti di tempo e frequenza ad alta accuratezza
Planar-Waveguide External Cavity Laser Stabilization for an Optical Link with 1E-19 Frequency Stability
We stabilized the frequency of a compact planar-waveguide external cavity
laser (ECL) on a Fabry-P\'erot cavity (FPC) through a Pound-Drever-Hall scheme.
The residual frequency stability of the ECL is 1E-14, comparable to the
stability achievable with a fiber laser (FL) locked to a FPC through the same
scheme. We set up an optical link of 100 km, based on fiber spools, that
reaches 1E-19 relative stability, and we show that its performances using the
ECL or FL are comparable. Thus ECLs could serve as an excellent replacement for
FLs in optical links where cost-effectiveness and robustness are important
considerations
effect of a timebase mismatch in two way optical frequency transfer
Two-way frequency transfer on optical fibers is a powerful technique for the comparison of distant clocks over long and ultra-long hauls. In contrast to traditional Doppler noise cancellation, it is capable of sustaining higher link attenuation, mitigating the need of optical amplification and regeneration and thus reducing the setup complexity. We investigate the ultimate limitations of the two-way approach on a 300 km multiplexed fiber haul, considering fully independent setups and acquisition systems at the two link ends. We derive a theoretical model to predict the performance deterioration due to a bad synchronisation of the measurements, which is confirmed by experimental results. This study demonstrates that two-way optical frequency transfer is a reliable and performing technique, capable of sustaining remote clocks comparisons at the resolution, and is relevant for the development of a fiber network of continental scale for frequency metrology in Europe
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