Xavier Vacheret

Advanced bridge instrument for the measurement of the phase noise and of the short-term frequency stability of ultra-stable quartz resonators

This article reports on the advances in the characterization of an instrument intended to test 5 MHz and 10 MHz crystal resonators packaged in HC40 enclosure, that used for the high-stability space resonators. Improvements concern the design of new double ovens, the reduction of the residual carrier, a lower drift, and a modified calibration process. The instrument sensitivity, that is, the background phase noise converted into Allan deviation, is of 10-14.

About Quartz Crystal Resonator Noise: Recent Study

The first step, before investigating physical origins of noise in resonators, is to investigate correlations between external measurement parameters and the resonator noise. Tests and measurements are mainly performed on an advanced phase noise measurement system, recently set up. The resonator noise is examined as a function of the sensitivity to the drive level, the temperature operating point and the tuning capacitor.

Thermal characterization of crystal ovens used in phase noise measurement system

In this paper, the thermal stability characterization of crystal ovens used in a phase noise measurement system of ultra-low noise crystal resonators is proposed. This bench is dedicated to test 5 MHz and 10 MHz crystal devices packaged in HC40 enclosures. New double ovens have been designed to improve the ultimate noise floor of our carrier suppression bench. A brief description of the temperature environment and processing are given. In addition, experiments to measure the thermal stability of the oven control are given. These new crystal ovens present an Allan standard deviation of about 2-10-15 at 1 s in terms of relative frequency fluctuations

The effect of power-drive level on the calibration of the bridge instrument for the measurement of the quartz stability

In this paper, it is shown that the amplitude-frequency effect, a well known phenomenon in quartz crystal resonator, questions the short-term stability results of quartz crystal resonators computed from phase noise measurement in passive interferometer systems. This equipment allows one to measure the inherent phase stability of quartz crystal resonators in a passive circuit without the noise usually associated with an active oscillator. The short-term stability of the resonator given by the Allan standard deviation is usually computed with the Leeson frequency. A new method to characterize the short-term stability of crystal resonators by a phase bridge system is given.

Quality Factor Measurements of Various Types of Quartz Crystal Resonators Operating Near 4 K

Quartz crystal resonators can exhibit huge quality factors (in excess of 1 billion) at liquid-helium temperature. However, they must satisfy a set of conditions to meet this high level of performance. With the help of experimentation, the main conditions are identified, such as the material quality, the energy trapping due to the vibrational mode structure, as well as the corresponding influence of the support mechanism and the effects of the electrodes.

A new method of probing mechanical losses of coatings at cryogenic temperatures

A new method of probing mechanical losses and comparing the corresponding deposition processes of metallic and dielectric coatings in 1-100 MHz frequency range and cryogenic temperatures is presented. The method is based on the use of high-quality quartz acoustic cavities whose internal losses are orders of magnitude lower than any available coating nowadays. The approach is demonstrated for chromium, chromium/gold, and multilayer tantala/silica coatings. The Ta2O5/SiO2 coating has been found to exhibit a loss angle lower than 1.6 × 10-5 near 30 MHz at 4 K. The results are compared to the previous measurements.

Development of a 5 MHz frequency difference pre-multiplier for a short term frequency stability bench of the oscillators

This paper reports the realization of a 5 MHz frequency difference x10 pre-multiplier, developed in the laboratory to replace an obsolete one. The principle we chose is to synthesize a 45 MHz and a 50 MHz from a reference signal and from the signal to be measured, and to subtract one to the other to generate a 5 MHz, whose precision on the measurement is increased by a factor 10. Obtained Allan variance sigmay(tau) at 1 s is 5.10-14 and output spectral density of phase noise floor is about -160 dBc/Hz at 5 MHz.

Temperature coefficients of quartz at cryogenic temperature

The temperature coefficients of the elastic coefficients of quartz within [4 K, 15 K], the operating range of conventional cryocoolers, are predicted from experimental data. Raw data consist of a set of frequency-temperature curves recorded from bulk acoustic wave resonators made in different plates cut according to various angles relative to the crystallographic axes. Raw data are then processed as described in the paper in order to provide the 1st, 2nd, and 3rd order temperature coefficients of the seven elastic coefficients of quartz crystal.

Impact of coatings on the quality factor of a quartz crystal resonator at liquid helium temperature

Effects of coatings on the quality factor of quartz crystal resonators operating at liquid helium temperature are analyzed. A first set of tests demonstrates the effects of gold and chromium electrodes at low temperature. The second set of tests involves a multilayer tantala/silica coating used to reach an extreme reflectance on mirrors such those used in optical cavities or Michelson interferometers. Mechanical losses are measured and discussed from the theoretical model the most frequently used.