The highly accurate time and frequency transfers need stable underlying line and knowledge of its parameters. The relativistic effects must be considered - especially at oneway transfers the Sagnac correction must be evaluated. In our previous work we proposed automated method for estimation of Sagnac correction for links with unknown or uncertain paths. This paper proposes a new idea of using artificial paths for comparison of Sagnac correction estimation approaches.
For long distance transmission of highly accurate time or stable frequency it is important to keep the reciprocal propagation path. It allows us to improve transmission stability (slow effect will cancel in first order) and also to establish active compensation of propagation fluctuations. Unfortunately, single fiber transmission introduces necessity of bidirectional symmetrical amplifiers in order not to lose advantage of a reciprocal path. In case of time transfer, quasi-bidirectional amplification might be acceptable. It means that amplifiers contain short nonreciprocal path, e.g. wavelength routers or even active fibers. But the ultra-stable frequency transfer requires truly single path optical amplifiers that are considered further. This paper proposes the new idea of using bidirectional EDFA amplifier with optical channel monitor for to detect and suppress unwanted laser of amplifier.
This paper presents a novel algorithm for preprocessing of pulses coming from GNSS and signals produced locally by a rubidium oscillator to reduce synchronization time without changing the main algorithm of the control loop. Moving average and Kalman filtration were used as the preprocessing methods. The experimental results for different rubidium oscillators are presented.
In contrast to quartz crystal microbalances, the sensitivity of thin film bulk acoustic wave resonators (FBARs) is strongly dependent on all layers composing the composite structure. Previous studies of the pure mass sensitivity of suspended FBARs, proved that placing low acoustic impedance materials at the sensing surface of the device can enhance their sensitivity by carefully controlling the energy trapping effects. Here we extend those studies by investigating if the in-liquid sensitivity of shear-mode AlN-based solidly mounted resonators (SMRs), working at 2 GHz, display a similar dependence on the device configuration (top electrode thickness and material). We use the finite element method (FEM) and experimental results to demonstrate that if one is restricted by the readout circuit to a certain resonant frequency, the sensitivity of the devices (particularly in-liquid sensors or biosensors) can be boosted by proper design while preserving the initial frequency. This is possible since the variations in sensitivity are strongly dependent on the energy distribution within the whole resonant structure.
With the rapid development of science and technology, the demand for time and time signal is getting higher and higher by users in various fields. Most of the world's time laboratories use high performance cesium clocks and hydrogen masers for timekeeping in order to ensure the accuracy and stability of their atomic time scale. The hydrogen maser has excellent stability. However, the hydrogen maser has frequency drift, and the inaccurate deduction of the frequency drift of the maser will affect the accuracy of the atomic time calculation directly. Therefore, in this paper, a method based on the minimum error theory is used to estimate the frequency drift parameter of masers in a certain time interval. Three hydrogen masers operated in NTSC (National Time Service Center) are used to determine the frequency drift parameter. After removing hydrogen maser frequency drift, we use exponential filtering method to calculate the time scale based on hydrogen masers. At the same time, according to the frequency drift parameters of the hydrogen masers published in BIPM Circular T, the frequency drift is deducted and the time scale is calculated. The former is a dynamic estimation of the drift and the initial values is set to the values which come from Circular T. Then the comparative analysis is made at the end. The results show that the method based on minimum error theory can accurately estimate the drift of hydrogen maser, and the accuracy of this time scale is significantly higher than another atomic time scale, and the absolute value of maximum deviation with TA(NTSC) is 3.51ns.
Sc-doped AlN polycrystalline films are attractive active layers for high frequency (GHz range) acoustic resonators owing to the significant enlargement of the AlN piezoelectric activity with the increasing Sc content. To sputter homogenously doped AlScN films on 200 mm Si wafers we use a configurable cathode containing a variable number of embedded Sc pellets to fine tuning the Sc content in the films. The method was implemented in an Endeavor-AT™ cluster tool from OEM Group, adapted for sputtering on 200 mm wafers. 1 μm thick AlScN films with uniform Sc content (around 7 at.%), high crystal quality and good piezoelectric response have been sputtered over 200 mm production-level wafers.
The operation of a large frame ring laser gyroscope (RLG) with ultimate sensitivity requires the development of a very careful active control of the ring geometry. This can be obtained in a square ring by measuring against a reference laser the diagonals length and eventually implementing a procedure to equalize them. The technique to measure and to stabilize the diagonals has been tested on GP2, a RLG of reduced dimension installed in INFN laboratories in Pisa. A resolution better than 1 ppm, limited by the local anthropic noise, has been obtained.
We describe the design of time distribution for the SKA using WR with DWDM optics. Included are accuracy estimates accounting for temperature, dispersion, calibration, attenuation, wavelength uncertainty and the Sagnac effect, and experimental results on long distance links.
We report preliminary results of dark mater searches within the worldwide network made of our laboratories. We demonstrate that data routinely collected by our currently operating optical atomic clocks without any further developments of the experimental set-ups may be used to run a global program aimed on searches of dark matter.
We present the status of the industrialization activity of a Rubidium POP (Pulsed Optically Pumped) clock Physics Package (PP) designed to meet the harsh space environment and more than 12 years of life-time. Leonardo completed the design phase including thermal, mechanical and magnetic analyses. PP manufacturing started at the beginning of 2018. The vibration test on the full microwave cavity assembly prototype including the Rb cell is foreseen by the first half of the year. The target for the Rb POP industrialization activity is to achieve a space qualification of the full clock by 2020 and the readiness for experimental flight by 2022.
Microwave signals with unprecedented ultra-low phase noise can be generated by photo-detecting stabilized optical pulse trains from femtosecond laser. However, excess noise introduced by photodetection limits the phase noise performance of generated microwave signals. Here, we demonstrate a new limitation that arises from the pulse duration fluctuation of ultrashort optical pulses. Such fluctuations, although minute compared to the pulse duration itself, convert to phase fluctuations in the microwave electrical waveforms generated by photodetection in a fast InGaAS pin photodiode, due to nonlinear processes. We quantitatively characterize the pulse duration to phase conversion coefficient under various experimental configurations (bias voltage, optical power, etc). Furthermore, by combining this quantitative characterization with experimental microwave phase noise measurement under conditions where this new effect is the dominant source of noise, we have characterized quantitatively, to our knowledge for the first time, the pulse duration noise that is present at the output of an Erbium doped fiber based femtosecond laser and its optical amplification chain.
Russian-Chinese Cooperation Committee on Satellite Navigation was established by the two sides of China and Russia under the regular meeting mechanism, In order to effectively pro-mote the cooperation between China and Russia in the field of satellite navigation. The technical communication of existing and future compatibility, interoperability and time system interoperability, etc was established by the committee. UTC(NTSC) and UTC(SU) joint time scale is a unified reference for compatibility and interoperability of GLONASS and BeiDou navigation system. The unified reference is necessary for effectively promoting the cooperation between the two sides in the field of satellite navigation. In this paper, through atomic clock stability analysis, the linear prediction model was used for cesium clocks and the quadratic prediction model was used for hydrogen maser clocks. The weight of clock was determined by the ‘predictability’ of clock. UTC(NTSC) and UTC(SU) joint time scale and the time scale generated using only the NTSC laboratory atomic clocks was calculated from MJD 57754 to 58119. The results shows that the stability of the joint time scale is better than the stability of the time scale calculated using only the NTSC laboratory atomic clock.
Optical time transfer between PTB and Deutsche Telekom started in 2015. Since December 2016 it has been upgraded to a permanent installation connecting PTB and Deutsche Telekom facilities in Hannover and Bremen. In this paper we report on the evaluation of the performance of this installation and describe future perspectives.
The stability of the transmitted optical frequency in a single bidirectionally operated fiber was compared with stability in a link consisting of two separate unidirectional fibers. The measurements were performed in a standard closed-loop system canceling the fiber induced phase noise. It was found that phase fluctuations in the higher frequency band (acoustic noise) are well suppressed in both configurations (single bidirectional fiber and separate unidirectional fibers). The long-term drifts however are not fully compensated in a link consisting of two separate unidirectional fibers, but still about two orders of magnitude noise reduction was observed in comparison with not compensated transfer.
This paper compares the time synchronization performance of standard NTP versus NTP secured using the Network Time Security (NTS) protocol. The measurements were performed using the NTS software of Ostfalia University of Applied Science — the first implementation of NTS based on the IETF internet draft “draft-ietf-ntp-using-nts-for-ntp-06”. The measurements quantify the impact of the security measures on the time synchronization performance and allow conclusions to be drawn regarding efficiency and potential improvements to the protocol.
A first vibrating inertial quartz gyrometer with gold nanoparticles electrodes is presented in this paper. Electrical measurements have shown enhancement of the quality factor compared to standard gyrometers with 200 nm evaporated gold electrodes.
This paper presents recent advances on two-dimensional Length-Extensional Modes (LEM) quartz micro-resonators providing high quality factor (Q) on resonances at a fewMHz. The resonators have been manufactured with a two teps Deep Reactive Ion Etching (DRIE) in a wafer level process reducing costs for collective realization. Samples vibrating at 2.2 and 3.0 MHz on the fundamental mode have shown promising results with very high Q exceeding 200,000. Best result obtained so far were obtained on a partial mode vibrating at 6.6 MHz reaching a Q of 250,000. The collective process, advantages of quartz and high Q make these resonators a promising candidate for Time & Frequency applications.
We present a comparison of time transfer results over European baselines obtained with two space-based techniques: Precise Point Positioning with integer ambiguity resolution (IPPP) using GPS satellites and Time Transfer by Laser Link (T2L2) using the low orbiting satellite Jason-2. The data was obtained in a 3-month experiment in Autumn 2013 for baselines between Paris, Herstmonceux and Grasse. We find that the difference between the 30-s IPPP link results and the closest 1-s T2L2 data points has a standard deviation below 100 ps for all three baselines. These results provide the basis for a continuous time transfer technique with accuracy at the 100 ps level for baselines over which T2L2 can operate in CV. Occasional T2L2 measurements provide the absolute time difference with a high accuracy and a continuous IPPP link maintains the accuracy for weeks to months between calibrations.
Galileo disseminates the GPS to Galileo Time Offset (GGTO) through the navigation message. This broadcast offset allows the user of a combined GSP/Galileo receiver to achieve a unique navigation solution by using measurements from both GPS and Galileo satellites. Nowadays, many positioning systems are available, the topic of interoperability is therefore crucial. The time offsets between the different systems should therefore be made available to the multi-GNSS users. An alternative would be that each constellation broadcasts only the time offset between its time scale and a reference common to all GNSS. In this paper we propose two alternative for, for this reference: either it can be based on the combination of the different GNSS time scales, or it can be directly UTC, as predicted and broadcast by the different systems. This paper presents a first assessment of the performances that can be achieved with each of these two approaches.
This document describes usage of optical network for linking of remote atomic clock to the Institute of Photonics and Electronics where is maintained the UTC(TP) time scale.
