Benoît Dubois

Quartz resonator instabilities under cryogenic conditions

The phase noise of a quartz crystal resonator working at liquid helium temperatures is studied. Measurement methods and the device environment are explained. The phase noise is measured for different resonance modes, excitation levels, amount of operating time, device orientations in relation to the cryocooler vibration axis, and temperatures. Stability limits of a frequency source based on such devices are evaluated in the present measurement conditions. The sources of phase flicker and white noises are identified. Finally, the results are compared with previous works.

Characterization of the Individual Short-Term Frequency Stability of Cryogenic Sapphire Oscillators at the

We present the characterization of three cryogenic sapphire oscillators (CSOs) using the three-cornered-hat method. Easily implemented with commercial components and instruments, this method reveals itself very useful to analyze the fractional frequency stability limitations of these state-of-the-art ultrastable oscillators. The best unit presents a fractional frequency stability better than 5 × 10-16 at 1 s and below 2 × 10-16 for τ <; 5000 s.

10^{-16}

A CMOS transistor ageing analytical model is presented and the procedure that allows to extract its parameters is proposed in this paper. By using a simple, example, we show how such a model can be used to forecast the drifts of the main characteristics of a CMOS circuit Further, we demonstrate that this model can also be used to help the designer to choose and/or modify a circuit in order to minimize the hot-carrier induced degradations. Simulation results compared to the analytical study are also shown

Level

We present the characterization of 8-12 GHz whispering gallery mode resonators machined in high-quality sapphire crystals manufactured with different growth techniques. These microwave resonators are intended to constitute the frequency reference of ultra-stable Cryogenic Sapphire Oscillators. We conducted systematic tests near 4 K to determine the unloaded Q-factor and the turnover temperature for whispering gallery modes in the 8-12 GHz frequency range. We have shown that high quality sapphire crystals manufactured with the Heat Exchange or the Kyropoulos growth technique are both suitable to meet a fractional frequency stability better than 1×10-15 for 1 s to 10,000 s integration times.

Analytical Modeling of Hot-Carrier Induced Degradation of MOS Transistor for Analog Design for Reliability

In this paper, we report the characterization results of our cryogenic sapphire oscillators. The oscillator incorporates a sapphire resonator cooled down at the liquid helium temperature in a cryocooled ultra-low vibration cryostat. The phase noise of a single CSO is -104dBc/Hz at 1 Hz offset of the 10 GHz carrier. The frequency fluctuations were measured with three frequency counters using different statistical algorithms. The best result at 1 s integration time is σy(1s) = 6.5 × 10-16. For the integration time above 10 s, the Allan deviation of a single CSOs computed from each data sets reaches a floor around 3.2 × 10-16 at 100 s integration time for a daily frequency stability of 3.5 × 10-15.

Tests of Sapphire Crystals Manufactured With Different Growth Processes for Ultra-Stable Microwave Oscillators

In this paper, we present the characterization results of three Cryogenic Sapphire Oscillators (CSO) by using the three-cornered hat method. The three-cornered hat method permits us to extract the individual frequency instabilities. Thus this powerful tool helps us to choose the best mechanical and thermal CSO configurations. We tested two frequency counters requiring two different data processing and get almost the same results. The three CSOs reach a frequency instability better than 7×10-16 between 1 s and 3,000 s integration times. The Allan deviation of the best CSO reaches a noise floor around 1.5×10-16 at 200 s integration time. Although, the new CSO incorporates a Kyropulos instead of a HEMEX sapphire resonator, it presents the almost the same frequency stability than the two other ones.

Latest improvements in the performances of a cryogenic sapphire oscillator

The ULISS Cryogenic Sapphire Oscillator (CSO) offers unprecedented short-term frequency performances. It was specially designed to be transportable by car in order to test this new technology in different European sites. During the last 18 months, it was used to qualify with success several high stability frequency sources. In February 2013, a new measurement campaign was lead at CNES, Toulouse (France) to qualify the flight model of the frequency synthesis of the PHARAO clock. During the same period we built a second CSO unit based on the same design and conducted new characterisations of frequency stability and environmental sensitivity. Optimisation of the system has led to an improved frequency stability reaching currently better than 1×10-15 at 10,000 s integration times. Eventually we developed a new low phase noise and high-resolution frequency synthesis delivering 10 GHz, 100 MHz and 9.192 GHz ultra stable signals. In this paper we draw a progress report on the ULISS project, updating performances and describing the latest experiments conducted with our CSO in different sites in Europe.

Characterization of a set of cryocooled sapphire oscillators at the 10 −16 level with the three-cornered hat method

State-of-the-art microwave ultra-stable oscillators are currently based on sapphire resonator operated in whispering gallery modes in the range 5 – 12 GHz. Indeed the best near carrier phase noise is achieved with commercial systems incorporating a room temperature sapphire reference associated with a sophisticated electronics degenerating the noise of the sustaining oscillator stage [1]. On the other part, relative frequency instabilities better than few 1 × 10−15 are achieved with laboratory Cryogenic Sapphire Oscillator (CSO) in which the sapphire crystal is cooled into a large liquid Helium dewar and maintained at its turnover temperature (between 5–8 K) [2]. More reccenlty, we demonstrated an original and reliable technology incorporating a pulse-tube cooler instead of a bath cryostat thus eliminating the need for regular supplies and manual transferring of liquid helium [3]. The advent of reliable and cryocooled (CSO) open the possibility to implement such an ultra-stable reference not only in metrological laboratories with liquid helium facilities but also in remote sites like base stations for space navigation, VBLI antenna sites, … This technology is today available through a newly created business unit: ULISS{su®) [4].

ULISS project: 2013 progress report

Optical frequency division of an ultrastable laser to the microwave frequency range by an optical frequency comb has allowed the generation of microwave signals with unprecedently high spectral purity and stability. However, the generated microwave signal will suffer from a very low power level if no external optical frequency comb repetition rate multiplication device is used. This paper reports theoretical and experimental studies on the beneficial use of the Vernier effect together with the spectral selective filtering in a double directional coupler add-drop optical fibre ring resonator to increase the comb repetition rate and generate high power microwaves. The studies are focused on two selective filtering aspects: the high rejection of undesirable optical modes of the frequency comb and the transmission of the desirable modes with the lowest possible loss. Moreover, the conservation of the frequency comb stability and linewidth at the resonator output is particularly considered. Accordingly, a fibre ring resonator is designed, fabricated, and characterized, and a technique to stabilize the resonator’s resonance comb is proposed. A significant power gain is achieved for the photonically generated beat note at 10 GHz. Routes to highly improve the performances of such proof-of-concept device are also discussed.

Properties of sapphire crystals elaborated with different grow technics for microwave ultra-stable oscillator applications

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.