Philippe Guillemot

10 MHz hyperstable quartz oscillators performances

New hyperstable quartz oscillators are presented. Methods to overcome limitations due to various noise sources are discussed. Stabilities down to 5.10/sup -14/ are obtained together with drift down to 5.10/sup -12//day and excellent resistance to bad environmental conditions. Progresses in minimizing oscillators phase noise have, in fact, been very slow. Short term stabilities lower than 10/sup -12/ began to be obtained 30 years ago. The first result lower than 10/sup -13/ was obtained in 1978 but could not be reproduced until the 90s. More recently, quartz oscillators with exceptionnally good short term stabilities were needed for various projects including cold atom space clocks in France and Linear Ion Trap Standard in United States. More precisely 10 MHz quartz oscillators with stabilities in the vicinity of 7/spl times/10/sup -14/ between 1 and 100 s were studied and designed. In view of this work, it has been necessary to study all different possible sources of noise so as to undertake noise reduction when possible for instance in resonator and in the electronic circuits. Various attempts to reduce noise in the oscillating loop are presented. The most recent results obtained in France and in United States on several units are presented and discussed pointing out that it seems now possible to routinely build such units.

Time Transfer by Laser Link - The T2L2 experiment on Jason-2 and further experiments

The new generation of optical time transfer will allow the synchronization of remote ultra stable clocks and the determination of their performances over intercontinental distances. The principle of T2L2 (Time Transfer by Laser Link) is based on the techniques of satellite laser ranging coupled with time-frequency metrology. It consists of synchronizing ground and space clocks using short laser pulses travelling between ground clocks and satellite equipment. The instrument will be integrated on the ocean altimetry satellite Jason-2 that is scheduled for launch in 2008.(a) The experiment should enhance the performance of time transfer by one or two magnitudes compared to existing microwave techniques such as GPS and Two-Way Satellite Time and Frequency Transfer (TWSTFT).

Long-term operation and performance of cryogenic sapphire oscillators

Cryogenic sapphire oscillators (CSO) developed at the University of Western Australia (UWA) have now been in operation around the world continuously for many years. Such oscillators, due to their excellent spectral purity are essential for interrogating atomic frequency standards at the limit of quantum projection noise; otherwise aliasing effects will dominate the frequency stability due to the periodic sampling between successive interrogations of the atomic transition. Other applications, which have attracted attention in recent years, include tests on fundamental principles of physics, such as tests of Lorentz invariance. This paper reports on the long-term operation and performance of such oscillators. We compare the long-term drift of some different CSOs. The drift rates turn out to be linear over many years and in the same direction. However, the magnitude seems to vary by more than one order of magnitude between the oscillators, ranging from 1014 per day to a few parts in 1013 per day

Time transfer by laser link (T2L2): characterization and calibration of the flight instrument

The T2L2 project (time transfer by laser link) allows for the synchronization of remote ultra-stable clocks over intercontinental distances (Fridelance et al 1997 Exp. Astron. 7, Samain and Fridelance 1998 Metrologia 35 151–9). The principle is derived from satellite laser ranging technology with dedicated space equipment designed to record arrival times of laser pulses at the satellite. The space segment has been launched in June 2008 as a passenger experiment on the ocean altimetry satellite Jason 2. T2L2 had been specified to yield a time stability of better than 1 ps over 1000 s integration time and an accuracy of better than 100 ps. This level of performance requires a rigorous data processing which can be performed only with a comprehensive calibration model of the whole instrumentation. For this purpose, several experimental measurements have been performed before and during the integration phase of the T2L2 space instrument. This instrument model is one of the cornerstones of the data reduction process which is carried out to translate the raw information to a usable picosecond time transfer. After providing a global synopsis of the T2L2 space instrument, the paper gives a description of the experimental setup for the instrument characterization. It then details the different contributions within the calibration model and concludes with an applied example of a space to ground time transfer.

Time transfer by laser link: a complete analysis of the uncertainty budget

The Time Transfer by Laser Experiment (T2L2) on the Jason 2 satellite is a mission allowing remote clocks synchronization at the picosecond level. It is based on laser ranging technologies, with a laser station network on the ground and a dedicated instrument on board the satellite. It was launched in June 2008 and has been working continuously since then. T2L2 performances are very promising for time and frequency metrology and also for fundamental physics. The scientific objectives of the whole experiment rely on a rigorous uncertainty budget. This is governed by the characteristics of the space instrument and the laser stations network, the post treatment done on the ground, and also the process used to calibrate the laser stations. The uncertainty budget demonstrates that T2L2 is able to perform common-view time transfers between remote sites with an expanded uncertainty better than 140 ps (coverage factor = 2).

Time Transfer by Laser Link: The T2L2 experiment on Jason 2

The new generation of optical time transfer (T2L2 - Time Transfer by Laser Link) under development at OCA and CNES will allow the synchronization of remote ultra stable clocks and the determination of their performances over intercontinental distances. The principle is based on the propagation of light pulses between the clocks that are to be synchronized. T2L2 is the follow-on mission to LASSO (LAser Synchronization from Stationary Orbit) with performances improved by two orders of magnitude. Expected T2L2 performances are in the 100 ps range for accuracy, with an ultimate stability better than 1ps over 1,000s and than 10ps over one day. After a short overview of the instrumental heritage and the historic course of the project up to todays acceptation on Jason 2, we will report on a ground experiment conducted by OCA permitting to envision a performance improvement of at least one order of magnitude as compared to the best time transfer techniques available. Then preliminary performance budgets for the T2L2 on Jason 2 mission will be given, based on measurements conducted by OCA and expected performances of the space instrument. We will finish with the status of the space instrument development and a summary of recently conducted measurements of the electronics breadboards performances

Slowly varying function method applied to quartz crystal oscillator transient calculation

By using an approach based on the full nonlinear Barkhausen criterion, it is possible to describe oscillator behavior under the form of a nonlinear characteristic polynomial whose coefficients are functions of the circuit components and of the oscillation amplitude. Solving the polynomial in the frequency domain leads to the steady state oscillation amplitude and frequency. In the time domain, the characteristic polynomial represents a nonlinear differential equation whose solution gives the oscillator signal transient. It is shown how symbolic manipulation capabilities of commercially available softwares can be used to automatically generate the coding of the oscillator characteristic polynomial from the SPICE description netlist. The numerical processing of such an equation in the time domain leads to unacceptable computer time because of the high quality factor of the oscillator circuits involved. Nevertheless, by using the slowly varying amplitude and phase method, it is possible to transform the initial nonlinear differential equation into a nonlinear first order differential equation system in the amplitude and phase variables. The solution of this system directly gives the designer the most relevant features of the oscillation; that is, the amplitude, phase, or frequency transients which can be accurately obtained within a short computer time by using classical numerical algorithms.

Time and frequency distribution improvement in Calern/Geoazur laboratory for T2L2 campaigns

The Time Transfer by Laser Link (T2L2)[1) experiment aim to synchronise remote ultra stable clocks over large-scaled distances using two laser ranging stations. T2L2 ultimate time transfer capability can only be demonstrate with a picosecond range ground mastering. We focus this year in knowledge and equipment improvement to perform a T2L2 time transfer with accuracy and stability of a few picoseconds. A deep analysis of signals stability has been carried out this year in the time and frequency laboratory in Plateau de Calern. The aim was to better understand the limits and hardware configuration and to enhance time and frequency distribution for T2L2 experiment. We showed phase noise and stability problem on our H-maser distribution. Final measures were conducted in October in collaboration with SYRTE. Then a complete equipment reorganisation was done. This paper focus on the time and frequency laboratory characterization before and after the reorganisation. We introduce our new equipments and present our new H-maser time scale and discuss the performances obtained.

Automatic formal derivation of the oscillation condition

The behavior of a quartz crystal oscillator can be described by a nonlinear characteristic polynomial whose coefficients are function of the circuit parameters. Solving the polynomial in the frequency domain leads to the steady state oscillation amplitude and frequency. In the time domain, it gives the oscillator signal transient. Deriving the characteristic polynomial from the circuit description involves lengthy and tedious algebraic calculations if they are performed by hand. They may be now performed by using the symbolic manipulation capabilities of commercially available softwares. However, symbolic analysis using brute force method inevitably leads to an explosion of terms in equations. The paper will present a fully automatic method for generating the coding of an oscillator characteristic polynomial directly from the SPICE description netlist. The code thus generated is eventually compiled and takes place in an oscillator library. Then it is linked with the numerical main program that solves the polynomials. Solutions to overcome problems related to automatic symbolic calculations are presented and discussed. It is shown that the method used leads to concise and efficient code.

T2L2 : Ground to ground Time Transfer

T2L2 (Time Transfer by Laser Link), developed by both CNES and OCA permits the synchronization of remote ultra stable clocks over intercontinental distances. The principle is derived from laser telemetry technology with a dedicated space equipment deigned to record arrival times of laser pulses at the satellite. Using laser pulses instead of radio frequency signals used in classical time transfer techniques (GPS, TWSTFT), T2L2 permits to realize some links between distant clocks with time stability of a few picoseconds and accuracy better than 100 ps.