A Low Power Cryogenic Sapphire Oscillator with better than 10-15 short term frequency stability

International audienceIn the field of Time and Frequency metrology, the most stable frequency source is based on a microwave whispering gallery mode sapphire resonator cooled near 6 K. Provided the resonator environment is sufficiently free of vibration and temperature fluctuation, the Cryogenic Sapphire Oscillator (CSO) presents a short term fractional frequency stability of better than 1 x 10-15. The recent demonstration of a low maintenance CSO based on a pulse-tube cryocooler paves the way for its deployment in real field applications. The main drawback which limits the deployment of the CSO technology is the large electrical consumption (three-phase 8 kW peak / 6 kW stable operation) of the current system. In this paper, we describe an optimized cryostat designed to operate with a low consumption cryocooler requiring only 3 kW single phase of input power to cool down to 4 K a sapphire resonator.We demonstrate that the proposed design is compatible with reaching a state-of-the-art frequency stabilit

Ultra-stable microwave cryogenic oscillator operated with a Gifford-McMahon cryocooler

International audienceWe demonstrate for the first time an ultra-stable microwave cryogenic oscillator operated with a Gifford-McMahon (GM) cryocooler. Despite the high level of vibration generated by the GM, we show that an optimised design, with simple passive solutions, enables a sufficient mechanical decoupling to achieve a state-of-the-art frequency stability. The implemented 10 GHz cryogenic oscillator features a fractional frequency stability (ADEV, Allan deviation) σy(τ ) < 3×10−15 for 1 s ≤ τ ≤ 104 s

A Low Power Cryocooled Autonomous Ultra-Stable Oscillator

International audienceWe present the design and the preliminary evaluation of a cryostat equipped with a low power pulse-tube cryocooler intended to maintain near 5 K a high-Q factor sapphire microwave resonator. This cooled resonator constitutes the frequency reference of an ultra-stable oscillator presenting a short term fractional frequency stability of better than 1×10-15. The proposed design enables to reach a state-of-the-art frequency stability with a cryogenic oscillator consuming only 3 kW of electrical power

Reliability and Reproducibility of the Cryogenic Sapphire Oscillator Technology

International audienceThe cryogenic sapphire oscillator (CSO) is a highly specializedmachine, which delivers a microwave reference signal exhibiting thelowest frequency fluctuations [Allan deviation (ADEV) <span class="MathJax" id="MathJax-Element-9-Frame" tabindex="0" style=""&gt<nobr&gt<span class="math" id="MathJax-Span-57" style="width: 2.78em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 2.315em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.426em, 1002.22em, 2.749em, -1000em); top: -2.315em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-58"&gt<span class="msubsup" id="MathJax-Span-59"&gt<span style="display: inline-block; position: relative; width: 0.997em; height: 0px;"&gt<span style="position: absolute; clip: rect(3.412em, 1000.57em, 4.131em, -1000em); top: -3.981em; left: 0em;"&gt<span class="mi" id="MathJax-Span-60" style="font-family: MathJax_Math; font-style: italic;"&gtσ</span&gt</span&gt<span style="position: absolute; top: -3.831em; left: 0.571em;"&gt<span class="texatom"id="MathJax-Span-61"&gt<span class="mrow" id="MathJax-Span-62"&gt<span class="mi" id="MathJax-Span-63" style="font-size: 70.7%; font-family: MathJax_Math; font-style: italic;"&gty</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt<span class="mo"id="MathJax-Span-64" style="font-family: MathJax_Main;"&gt(</span&gt<span class="mi" id="MathJax-Span-65" style="font-family: MathJax_Math; font-style: italic;"&gtτ</span&gt<span class="mo"id="MathJax-Span-66" style="font-family: MathJax_Main;"&gt)</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gt] for the integration time <span class="MathJax" id="MathJax-Element-10-Frame" tabindex="0" style=""&gt<nobr&gt<span class="math" id="MathJax-Span-67" style="width: 0.604em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 0.509em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.745em, 1000.51em, 2.467em, -1000em); top: -2.315em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-68"&gt<span class="mi" id="MathJax-Span-69" style="font-family: MathJax_Math; font-style: italic;"&gtτ</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gtbetween 1 and <span class="MathJax" id="MathJax-Element-11-Frame"tabindex="0" style=""&gt<nobr&gt<span class="math" id="MathJax-Span-70"style="width: 1.762em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 1.435em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.165em, 1001.44em, 2.337em, -1000em); top: -2.176em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-71"&gt<span class="msubsup" id="MathJax-Span-72"&gt<span style="display: inline-block; position: relative; width: 1.429em; height: 0px;"&gt<span style="position: absolute; clip: rect(3.177em, 1000.96em, 4.142em, -1000em); top: -3.981em; left: 0em;"&gt<span class="mn" id="MathJax-Span-73" style="font-family: MathJax_Main;"&gt10</span&gt</span&gt<span style="position: absolute; top: -4.374em; left: 1em;"&gt<span class="texatom" id="MathJax-Span-74"&gt<span class="mrow" id="MathJax-Span-75"&gt<span class="mn" id="MathJax-Span-76" style="font-size: 70.7%; font-family: MathJax_Main;"&gt4</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gts, indeed four decades. In such interval, good units feature<span class="MathJax" id="MathJax-Element-12-Frame" tabindex="0"style=""&gt<nobr&gt<span class="math" id="MathJax-Span-77" style="width: 7.178em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 5.972em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.312em, 1005.97em, 2.749em, -1000em); top: -2.315em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-78"&gt<span class="msubsup" id="MathJax-Span-79"&gt<span style="display: inline-block; position: relative; width: 0.997em; height: 0px;"&gt<span style="position: absolute; clip: rect(3.412em, 1000.57em, 4.131em, -1000em); top: -3.981em; left: 0em;"&gt<span class="mi" id="MathJax-Span-80" style="font-family: MathJax_Math; font-style: italic;"&gtσ</span&gt</span&gt<span style="position: absolute; top: -3.831em; left: 0.571em;"&gt<span class="texatom"id="MathJax-Span-81"&gt<span class="mrow" id="MathJax-Span-82"&gt<span class="mi" id="MathJax-Span-83" style="font-size: 70.7%; font-family: MathJax_Math; font-style: italic;"&gty</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt<span class="mo"id="MathJax-Span-84" style="font-family: MathJax_Main;"&gt(</span&gt<span class="mi" id="MathJax-Span-85" style="font-family: MathJax_Math; font-style: italic;"&gtτ</span&gt<span class="mo"id="MathJax-Span-86" style="font-family: MathJax_Main;"&gt)</span&gt<span class="mo" id="MathJax-Span-87" style="font-family: MathJax_Main; padding-left: 0.278em;"&gt&lt;</span&gt<span class="msubsup"id="MathJax-Span-88" style="padding-left: 0.278em;"&gt<span style="display: inline-block; position: relative; width: 2.332em; height: 0px;"&gt<span style="position: absolute; clip: rect(3.177em, 1000.96em, 4.142em, -1000em); top: -3.981em; left: 0em;"&gt<span class="mn"id="MathJax-Span-89" style="font-family: MathJax_Main;"&gt10</span&gt</span&gt<span style="position: absolute; top: -4.374em; left: 1em;"&gt<span class="texatom" id="MathJax-Span-90"&gt<span class="mrow" id="MathJax-Span-91"&gt<span class="mo" id="MathJax-Span-92" style="font-size: 70.7%; font-family: MathJax_Main;"&gt−</span&gt<span class="mn" id="MathJax-Span-93" style="font-size: 70.7%; font-family: MathJax_Main;"&gt15</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gt, with <span class="MathJax" id="MathJax-Element-13-Frame"tabindex="0" style=""&gt<nobr&gt<span class="math" id="MathJax-Span-94"style="width: 4.076em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 3.38em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.212em, 1003.38em, 2.401em, -1000em); top: -2.222em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-95"&gt<span class="mo" id="MathJax-Span-96" style="font-family: MathJax_Main;"&gt&lt;</span&gt<span class="msubsup" id="MathJax-Span-97" style="padding-left: 0.278em;"&gt<span style="display: inline-block; position: relative; width: 2.332em; height: 0px;"&gt<span style="position: absolute; clip: rect(3.177em, 1000.96em, 4.142em, -1000em); top: -3.981em; left: 0em;"&gt<span class="mn"id="MathJax-Span-98" style="font-family: MathJax_Main;"&gt10</span&gt</span&gt<span style="position: absolute; top: -4.374em; left: 1em;"&gt<span class="texatom" id="MathJax-Span-99"&gt<span class="mrow" id="MathJax-Span-100"&gt<span class="mo" id="MathJax-Span-101" style="font-size: 70.7%; font-family: MathJax_Main;"&gt−</span&gt<span class="mn" id="MathJax-Span-102" style="font-size: 70.7%; font-family: MathJax_Main;"&gt14</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gtdrift in one day. The oscillator is based on a sapphire monocrystalresonating at 10 GHz in a whispering-gallery mode, cooled at<span class="MathJax" id="MathJax-Element-14-Frame" tabindex="0"style=""&gt<nobr&gt<span class="math" id="MathJax-Span-103" style="width: 1.9em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 1.574em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.417em, 1001.53em, 2.383em, -1000em); top: -2.222em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-104"&gt<span class="mo" id="MathJax-Span-105" style="font-family: MathJax_Main;"&gt≈</span&gt<span class="mn" id="MathJax-Span-106" style="font-family: MathJax_Main; padding-left: 0.278em;"&gt6</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gtK for zero thermal coefficient and optimal quality factor<span class="MathJax" id="MathJax-Element-15-Frame" tabindex="0"style=""&gt<nobr&gt<span class="math" id="MathJax-Span-107" style="width: 0.975em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 0.787em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.472em, 1000.74em, 2.648em, -1000em); top: -2.315em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-108"&gt<span class="mi" id="MathJax-Span-109" style="font-family: MathJax_Math; font-style: italic;"&gtQ</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gt. We report on the progress accomplished in implementing 11 CSOs inabout ten years since the first sample was delivered to theMalargüe station of the European Space Agency (ESA) in Argentina.Short-term stability is improved by a factor of 3–10, depending on<span class="MathJax" id="MathJax-Element-16-Frame" tabindex="0"style=""&gt<nobr&gt<span class="math" id="MathJax-Span-110" style="width: 0.604em; display: inline-block;"&gt<span style="display: inline-block; position: relative; width: 0.509em; height: 0px; font-size: 120%;"&gt<span style="position: absolute; clip: rect(1.745em, 1000.51em, 2.467em, -1000em); top: -2.315em; left: 0em;"&gt<span class="mrow" id="MathJax-Span-111"&gt<span class="mi" id="MathJax-Span-112" style="font-family: MathJax_Math; font-style: italic;"&gtτ</span&gt</span&gt</span&gt</span&gt</span&gt</nobr&gt</span&gt, and the refrigerator’s electric power is reduced to a 3-kWsingle-phase line. Frequency stability and overall performances arereproducible, with unattended operation between scheduledmaintenance every two years. The CSO is now a semicommercialproduct suitable to scientific applications requiring extremefrequency stability with the reliable unattended long-termoperation, like the flywheel for primary frequency standards, theground segment of global navigation satellite system (GNSS),astrometry, very long baseline interferometry (VLBI), and radioastronomy stations

Technology Readiness of the Cryogenic Sapphire Oscillator.

International audienceThe cryogenic sapphire oscillator (CSO) delivers a reference signal exhibiting the lowest frequency fluctuations. For<br&gtthe best units, the Allan deviation (ADEV) is σy(τ ) &lt; 10−15 for integration time between 1 and 104 s, with a drift &lt; 10−14 in one day. The oscillator is based on a sapphire monocrystal resonating at 10 GHz in a whispering-gallery mode, cooled at 6 K for highest Q-factor and zero thermal coefficient. We report on the progress accomplished implementing eleven CSOs in about 10 years starting with the first sample delivered to the ESA station&nbsp; Argentina. Short- term stability is improved by a factor of 3-10, depending on τ, and the refrigerators electric power is reduced to 3 kW. Frequency stability and overall performances are reproducible, with unattended operation between scheduled maintenance every two years. The CSO is suitable to scientific applications requiring extreme frequency stability with reliable long-term operation. For example, flywheel for primary frequency standards, ground segment of GNSS, astrometry, VLBI, and radio astronomy stations. The CSO technology developed at the FEMTO-ST Institute is now mature for deployment in real very demanding application