The Omega Counter, a Frequency Counter Based on the Linear Regression

This article introduces the {\Omega} counter, a frequency counter -- or a frequency-to-digital converter, in a different jargon -- based on the Linear Regression (LR) algorithm on time stamps. We discuss the noise of the electronics. We derive the statistical properties of the {\Omega} counter on rigorous mathematical basis, including the weighted measure and the frequency response. We describe an implementation based on a SoC, under test in our laboratory, and we compare the {\Omega} counter to the traditional {\Pi} and {\Lambda} counters. The LR exhibits optimum rejection of white phase noise, superior to that of the {\Pi} and {\Lambda} counters. White noise is the major practical problem of wideband digital electronics, both in the instrument internal circuits and in the fast processes which we may want to measure. The {\Omega} counter finds a natural application in the measurement of the Parabolic Variance, described in the companion article arXiv:1506.00687 [physics.data-an].Comment: 8 pages, 6 figure, 2 table

The Parabolic variance (PVAR), a wavelet variance based on least-square fit

This article introduces the Parabolic Variance (PVAR), a wavelet variance similar to the Allan variance, based on the Linear Regression (LR) of phase data. The companion article arXiv:1506.05009 [physics.ins-det] details the $\Omega$ frequency counter, which implements the LR estimate. The PVAR combines the advantages of AVAR and MVAR. PVAR is good for long-term analysis because the wavelet spans over $2 \tau$, the same of the AVAR wavelet; and good for short-term analysis because the response to white and flicker PM is $1/\tau^3$ and $1/\tau^2$, same as the MVAR. After setting the theoretical framework, we study the degrees of freedom and the confidence interval for the most common noise types. Then, we focus on the detection of a weak noise process at the transition - or corner - where a faster process rolls off. This new perspective raises the question of which variance detects the weak process with the shortest data record. Our simulations show that PVAR is a fortunate tradeoff. PVAR is superior to MVAR in all cases, exhibits the best ability to divide between fast noise phenomena (up to flicker FM), and is almost as good as AVAR for the detection of random walk and drift

Analysis of high quality superconducting resonators: consequences for TLS properties in amorphous oxides

$1/f$ noise caused by microscopic Two-Level Systems (TLS) is known to be very detrimental to the performance of superconducting quantum devices but the nature of these TLS is still poorly understood. Recent experiments with superconducting resonators indicates that interaction between TLS in the oxide at the film-substrate interface is not negligible. Here we present data on the loss and $1/f$ frequency noise from two different Nb resonators with and without Pt capping and discuss what conclusions can be drawn regarding the properties of TLS in amorphous oxides. We also estimate the concentration and dipole moment of the TLS.Comment: 8 pages, 5 figure

Ultra-low phase noise all-optical microwave generation setup based on commercial devices

In this paper, we present a very simple design based on commercial devices for the all-optical generation of ultra-low phase noise microwave signals. A commercial, fibered femtosecond laser is locked to a laser that is stabilized to a commercial ULE Fabry-Perot cavity. The 10 GHz microwave signal extracted from the femtosecond laser output exhibits a single sideband phase noise $\mathcal{L}(f)=-104 \ \mathrm{dBc}/\mathrm{Hz}$ at 1 Hz Fourier frequency, at the level of the best value obtained with such "microwave photonics" laboratory experiments \cite{Fortier2011}. Close-to-the-carrier ultra-low phase noise microwave signals will now be available in laboratories outside the frequency metrology field, opening up new possibilities in various domains.Comment: 8 pages, 3 figures. To be published in Applied Optics, early posting version available at http://www.opticsinfobase.org/ao/upcoming_pdf.cfm?id=23114

Influence of the ESR saturation on the power sensitivity of cryogenic sapphire resonators

Here, we study the paramagnetic ions behavior in presence of a strong microwave electromagnetic field sustained inside a cryogenic sapphire whispering gallery mode resonator. The high frequency measurement resolution that can be now achieved by comparing two CSOs permit for the first time to observe clearly the non-linearity of the resonator power sensitivity. These observations that in turn allow us to optimize the CSO operation, are well explained by the Electron Spin Resonance (ESR) saturation of the paramagnetic impurities contained in the sapphire crystal.Comment: 8 pages, 9 figure

A Cryogenic Sapphire Resonator Oscillator with 1e-16 mid-term fractional frequency stability

We report in this letter the outstanding frequency stability performances of an autonomous cryogenique sapphire oscillator presenting a flicker frequency noise floor below 2e-16 near 1,000 s of integration time and a long term Allan Deviation (ADEV) limited by a random walk process of 1e-18/sqr(tau). The frequency stability qualification at this level called for the implementation of sophisticated instrumentation associated with ultra-stable frequency references and ad hoq averaging and correlation methods.Comment: 4 pages, 2 figure

Frequency Stability Measurement of Cryogenic Sapphire Oscillators with a Multichannel Tracking DDS and the Two-Sample Covariance

open6sìThis article shows the first measurement of three 100 MHz signals exhibiting fluctuations from 2×10-16 to parts in 10-15 for integration time τ between 1 s and 1 day. Such stable signals are provided by three Cryogenic Sapphire Oscillators (CSOs) operating at about 10 GHz, also delivering the 100 MHz output via a dedicated synthesizer. The measurement is made possible by a 6-channel Tracking DDS (TDDS) and the two-sample covariance tool, used to estimate the Allan variance. The use of two TDDS channels per CSO enables high rejection of the instrument background noise. The covariance outperforms the Three-Cornered Hat (TCH) method in that the background converges to zero "out of the box", with no need of the hypothesis that the instrument channels are equally noisy, nor of more sophisticated techniques to estimate the background noise of each channel. Thanks to correlation and averaging, the instrument background (AVAR) rolls off with a slope 1/√m, the number of measurements, down to 10-18 at τ=104 s. For consistency check, we compare the results to the traditional TCH method beating the 10 GHz outputs down to the MHz region. Given the flexibility of the TDDS, our methods find immediate application to the measurement of the 250 MHz output of the FS combs.openCalosso, Claudio E; Vernotte, Francois; Giordano, Vincent; Fluhr, Christophe; Dubois, Benoit; Rubiola, EnricoCalosso, Claudio E; Vernotte, Francois; Giordano, Vincent; Fluhr, Christophe; Dubois, Benoit; Rubiola, Enric

Pound-locking for characterization of superconducting microresonators

We present a new application and implementation of the so-called Pound locking technique for the interrogation of superconducting microresonators. We discuss how by comparing against stable frequency sources this technique can be used to characterize properties of resonators that can not be accessed using traditional methods. Specifically, by analyzing the noise spectra and the Allan deviation we obtain valuable information about the nature of the noise in superconducting planar resonators. This technique also greatly improves the read-out accuracy and measurement throughput compared to conventional methods.Comment: 5 page