1,545 research outputs found
On the 1/f Frequency Noise in Ultra-Stable Quartz Oscillators
The frequency flicker of an oscillator, which appears as a 1/f^3 line in the
phase noise spectral density, and as a floor on the Allan variance plot,
originates from two basic phenomena, namely: (1) the 1/f phase noise turned
into 1/f frequency noise via the Leeson effect, and (2) the 1/f fluctuation of
the resonator natural frequency. The discussion on which is the dominant
effect, thus on how to improve the stability of the oscillator, has been going
on for years without giving a clear answer. This article tackles the question
by analyzing the phase noise spectrum of several commercial oscillators and
laboratory prototypes, and demonstrates that the fluctuation of the resonator
natural frequency is the dominant effect. The investigation method starts from
reverse engineering the oscillator phase noise in order to show that if the
Leeson effect was dominant, the resonator merit factor Q would be too low as
compared to the available technology.Comment: 20 pages, list of symbols, 1 table, 6 figures, 43 reference
Characterization of Zero-Bias Microwave Diode Power Detectors at Cryogenic Temperature
We present the characterization of commercial tunnel diode low-level
microwave power detectors at room and cryogenic temperatures. The sensitivity
as well as the output voltage noise of the tunnel diodes are measured as
functions of the applied microwave power, the signal frequency being 10 GHz. We
highlight strong variations of the diode characteristics when the applied
microwave power is higher than few microwatt. For a diode operating at K,
the differential gain increases from V/W to about V/W when
the power passes from dBm to dBm. The diode present a white
noise floor equivalent to a NEP of pW/ and
pW/ at 4 K and 300 K respectively. Its flicker noise is
equivalent to a relative amplitude noise power spectral density
~dB/Hz at K. Flicker noise is 10 dB
higher at room temperature.Comment: 8 pages and 16 figure
Tests of Sapphire Crystals Produced with Different Growth Processes for Ultra-stable Microwave Oscillators
We present the characterization of 8-12 GHz whispering gallery mode
resonators machined in high-quality sapphire crystals elaborated with different
growth techniques. These microwave resonators are intended to constitute the
reference frequency of ultra-stable Cryogenic Sapphire Oscillators. We
conducted systematic tests near 4 K on these crystals to determine the unloaded
Q-factor and the turnover temperature for whispering gallery modes in the 8-12
GHz frequency range. These characterizations show that high quality sapphire
crystals elaborated with the Heat Exchange or the Kyropoulos growth technique
are both suitable to meet a fractional frequency stability better than 1x10-15
for 1 s to 10.000 s integration times.Comment: 7 figure
DC-powered Fe3+:sapphire Maser and its Sensitivity to Ultraviolet Light
The zero-field Fe3+:sapphire whispering-gallery-mode maser oscillator
exhibits several alluring features: Its output is many orders of magnitude
brighter than that of an active hydrogen maser and thus far less degraded by
spontaneous-emission (Schawlow-Townes) and/or receiving-amplifier noise. Its
oscillator loop is confined to a piece of mono-crystalline rock bolted into a
metal can. Its quiet amplification combined with high resonator Q provide the
ingredients for exceptionally low phase noise. We here concentrate on novelties
addressing the fundamental conundrums and technical challenges that impede
progress. (1) Roasting: The "mase-ability" of sapphire depends significantly on
the chemical conditions under which it is grown and heat-treated. We provide
some fresh details and nuances here. (2) Simplification: This paper obviates
the need for a Ka-band synthesizer: it describes how a 31.3 GHz loop
oscillator, operating on the preferred WG pump mode, incorporating Pound
locking, was built from low-cost components. (3) "Dark Matter": A Siegman-level
analysis of the experimental data determines the substitutional concentration
of Fe3+ in HEMEX to be less than a part per billion prior to roasting and up to
a few hundred ppb afterwards. Chemical assays, using different techniques
(incl. glow discharge mass spectra spectroscopy and neutron activation
analysis) consistently indicate, however, that HEMEX contains iron at
concentrations of a few parts per million. Drawing from several
forgotten-about/under-appreciated papers, this substantial discrepancy is
addressed. (4) Excitons: Towards providing a new means of controlling the
Fe3+:sapph. system, a cryogenic sapphire ring was illuminated, whilst masing,
with UV light at wavelengths corresponding to known electronic and
charge-transfer (thus valence-altering) transitions. Preliminary experiments
are reported.Comment: pdf only; submitted to the proceedings of the 24th European Frequency
and Time Forum, 13-15th April, 201
On the degeneracy of whispering gallery modes in a high-Q sapphire microwave resonator
Cylindrical WGM resonators machined in high-quality sapphire monocrystal
cooled down to liquid helium temperature offer exceptionally-high Q-factors in
the microwave frequency domain. Such a resonator constitutes the core of an
ultra-stable oscillator featuring fractional frequency stability better than
1e-15 at short integration times. As in any cylindrical resonant structure, the
WGM resonator presents a two fold degeneracy. When a defect breaks the
cylindrical symmetry of the resonator, the WGMs split and appear as doublets.
In the high-quality sapphire resonator, the frequency separation of these twin
modes varies from one mode order to another with a maximum value of a few tens
of kHz. While the mode splitting for a given mode was considered until now
unpredictable and intrinsic to each resonator since resulting a priori from
randomly distributed defects. we show here, at the contrary, that the observed
mode splitting found on all the sapphire resonators whatever their origin
mainly comes from a perfectly determined defect resulting from the
manufacturing processes.Comment: 7 pages, 10 figure
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
Compact Yb optical atomic clock project: design principle and current status
We present the design of a compact optical clock based on the 435.5 nm transition in Yb. The ion trap will
be based on a micro-fabricated circuit, with surface electrodes generating a
trapping potential to localize a single Yb ion a few hundred m from the
electrodes. We present our trap design as well as simulations of the resulting
trapping pseudo-potential. We also present a compact, multi-channel wavelength
meter that will permit the frequency stabilization of the cooling, repumping
and clear-out lasers at 369.5 nm, 935.2 nm and 638.6 nm needed to cool the ion.
We use this wavelength meter to characterize and stabilize the frequency of
extended cavity diode lasers at 369.5 nm and 638.6 nm.Comment: 7 pages, 5 figures. Proc. of the 8th FSM 2015, Potsdam, Germany. To
be published in IOP Journal of Physics: Conference Serie
Bruit des oscillateurs et des résonateurs à quartz
Un des problÚmes qui se posent au concepteur des oscillateurs à quartz de haute stabilité est le bruit propre des résonateurs. Nous effectuons tout d'abord une brÚve description des principaux mécanismes susceptibles d'affecter la stabilité des oscillateurs et des résonateurs à quartz. Ensuite sont explicitées les grandeurs mises en jeu dans la métrologie des fréquences : la densité spectrale de bruit de phase dans le domaine spectral et la variance d'Allan dans le domaine temporel. Enfin nous présentons l'instrumentation utilisée et développée pour la mesure du bruit des oscillateurs en général et des résonateurs en particulier
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