We present implementation of precise time dissemination using the White Rabbit protocol over shared optical fibers within research backbones. It highlights advancements in synchronization accuracy, shared infrastructure efficiency, and implications for scientific and possible industrial applications.

With the increasing demand for ultra-precise time synchronization and frequency dissemination across various scientific, industrial, and communication fields, the Czech Republic has developed an innovative, non-commercial fiber-based infrastructure. This infrastructure serves as a shared platform, utilizing optical fibers to enable high-precision timing, coherent frequency transfer, and a newly implemented vibrational sensing capability. The project also addresses challenges posed by classical communication noise-particularly from Raman scattering-on quantum channels, especially for Quantum Key Distribution (QKD). By strategically separating classical and quantum channels into distinct wavelength bands, such as the C-band and O-band, the infrastructure achieves minimal interference while enabling multiple concurrent applications over shared fiber lines.

We report on developing, characterizing, and verifying a compact, monolithic laser interferometric assembly designed for high-precision two- and three-axis displacement measurements in coordinate positioning systems. The design targets OEM integration into advanced precision motion platforms, including nanometrology instruments, semiconductor manufacturing equipment, and ultra-high vacuum (UHV) environments. Using a single laser source, the assembly integrates multiple interferometers into a monolithic L-shaped base frame, enabling sub-nanometer periodic error in X-Y motion systems while minimizing geometric and thermal instabilities. The pre-aligned and pre-adjusted architecture simplifies integration, enhances long-term stability, and ensures consistent metrological performance. The system's verification protocol employs quadrature phase analysis and systematic error metrics to characterize performance and optimise assembly. The results indicate sub-nanometer measurement capability and suggest the system's suitability for scalable implementation in advanced coordinate metrology applications.

Our research efforts in displacement measurement interferometry focused on long-term drifts initiated an extended experimental investigation in the interferometric assemblies of our design. We aimed to analyze, characterize and tackle the long-term measurement stability, expressed as the zero-drift, with particular attention to the thermal effects. For the experimentation, we developed a thermostatic chamber equipped with active temperature regulation, an array of sensors and control electronics. With either the finely stabilized temperature or with the thermal cycling, we can carry out a range of investigations: verification of modified design or prototype interferometers, testing of production pieces, characterization of integrated assemblies and units in terms of the zero drift and the susceptibility to thermal effects -- the temperature sensitivity dL/dT, expressed in nm/K. With these experimental studies, we demonstrate the potential of the zero drift studies to contribute to the development and broader expansion of interferometric instrumentation.

Laser interferometers have served as the workhorses in the metrology of length for several decades. Their broader application brings further challenges, especially for longer measurement time-frames or outside the laboratory environment with strictly controlled conditions. As a part of our team’s activities aiming at characterizing and eliminating the effects of unstable temperature on interferometric length measurements, we report on successfully remodelling a differential interferometer’s optical arrangement focused on increasing resilience against temperature changes. The experimental characterization under constant temperature and subsequently under thermal load proved a tenfold decrease in short-term fluctuations and reduced sensitivity to temperature changes by a factor of 100.

There has been an increased focus on precise time and frequency transmission dissemination at a national and international level recently. We would like to present the situation in the Czech Republic, our strategy, approach, and our experience with a non-commercial, cost-effective solution that utilizes shared optical networks. The presented solution provides accurate time and stable frequency at a lower operational cost, utilizing the shared spectrum of the CESNET3 network infrastructure. We are committed to future developments and upgrades that will include the next wavelength bands and geographic extensions. Additionally, we have implemented bidirectional dark channels on various wavebands, which utilize shared leased fibers and offer bidirectional compensation for fiber losses. However, operating precise time and frequency requires a single path with bidirectional amplification performed by optical amplifiers, which are sensitive to feedback from the fiber line induced by back-scattering, and reflections, and which can cause unwanted oscillations. We have addressed this issue by carefully solving the interference with parallel data transmissions. In summary, we have implemented a cost-effective solution for precise time and frequency dissemination in the Czech Republic, which utilizes shared optical networks. We are committed to future developments, and we are also part of a consortium that plans to realize a Pan-European network to offer time and frequency services to a broad range of users.

In the ever-advancing realm of modern technology, the demand for unparalleled precision and stability in timekeeping and frequency control has surged to unprecedented heights. As our interconnected world rellies more than ever on intricate synchronization and seamless communication, the development of cutting-edge optical infrastructure has emerged as a cornerstone in meeting these exacting demands. There has been obvious increased continuous focus on precise time and frequency transmission dissemination at a national and international level recently. We would like to present the situation in the Czech Republic, our strategy, approach, and our experience with a non-commercial, costeffective solution that utilizes optical networks shared with other traffic. The presented solution provides accurate time and stable frequency at a lower operational cost, using the shared spectrum of the CESNET3 network infrastructure.

In the article, we introduce the Czech Infrastructure for Time and Frequency activity which is a non-commercial, open activity focused on the transfer of accurate time and very stable frequency using optical networks. The national optical infrastructure for time and frequency transfer is operated on top of the CESNET network infrastructure, to have operational costs under control. We briefly summarize the history of its development, together with the used types of optical transfer and its stabilization. We also address running and planned upgrades and future development plans regarding wavelength bands and considered geographic extensions.

The definition of both meter and second relies on precisely measured frequency. The convenient sources of such frequencies are lasers stabilized by molecular vapours. The He-Ne lasers stabilized by iodine vapours represent the cornerstone sources in the visible spectrum. On the other hand, the infrared spectrum (particularly 1550 nm C-band) is of metrological interest thanks to its cost-effective, readily available components. The widely used absorption media at 1550nm has been two acetylene isotopes (12C2H2, 13C2H2), while H13C14N represents an alternative covering a broader spectrum well corresponding to the telecommunication C-band.

The wide span and high density of lines in its rovibrational spectrum render hydrogen cyanide a useful spectroscopic media for referencing absolute frequencies of lasers in optical communication and dimensional metrology. We determined, for the first time to the best of our knowledge, the molecular transitions' center frequencies of the H13C14N isotope in the range from 1526 nm to 1566 nm with 1.3 × 10-10 fractional uncertainty. We investigated the molecular transitions with a highly coherent and widely tunable scanning laser that was precisely referenced to a hydrogen maser through an optical frequency comb. We demonstrated an approach to stabilize the operational conditions needed to maintain the constantly low pressure of the hydrogen cyanide to carry out the saturated spectroscopy with the third-harmonic synchronous demodulation. We demonstrated approximately a forty-fold improvement in the line centers' resolution compared to the previous result.

National time and frequency dissemination networks are being developed in many countries; also international connections are being established. In the contribution we present Czech Infrastructure for Time and Frequency as a non-commercial, open activity focused on the transfer of accurate time and very stable frequency using optical networks. The national optical infrastructure for time and frequency transfer is operated on top of the CESNET network infrastructure, to have operational cost under control. We also address actually running and planned upgrades and future development plans regarding wavelength bands and considered geographic extensions. We will also focus on creation of bidirectional dark channels on different wavebands within shared fibers together with bidirectional compensation of fiber losses. Single path bidirectional amplification utilizing lumped optical amplifiers is sensitive to feedback from fiber line like back scattering and reflections and in case of increased feedback can produce unwanted oscillations, which potentially interfere with parallel data transmissions. We will also briefly mention the CLONETS-DS project working on design study for coherent Pan-European time and frequency dissemination network, which would connect national networks and provide different services based on time and frequency for a wide range of users.

Article summarizes past and continuous development, and especially current state of Czech national research infrastructure for Clock Network Services and future development plans. The focus is on used transmission means and stabilization techniques, available and planned wavelength bands and also plans for geographic extensions.

We report on an instrument for calibration of the 8-mm length gauges, currently being developed and finalised at ISI. The design and construction were focused on elimination and compensation of the typical error sources associated with laser interferometric length measurement. The state-of-art four beam double-path differential plane interferometer with the common-path arrangement (with co-planar beams and co-axial arms) has its z-axis coincident with that of the calibrated gauge so that the system preserves Abbé principle. The differential arrangement efficiently reduces the metrological loop as the reference mirror of the interferometer is mounted on the preloaded grip holder of the tested sensor and the object (measurement) mirror simultaneously loading the measuring tip of the calibrated gauge. The latter is carried with a two-stage positioning comprising a precise linear ball bearing guide actuated with a DC motor (75 mm range, 2,6 mm/s velocity), and a triplet of piezoelectric elements that allow for a micro-positioning (0,015 mm range) and tilting of the object mirror. The displacement readout, compensated for the refractive index of air fluctuations using temperature, pressure and humidity sensors, provides feedback for the stabilisation of the object mirror position in the z-axis (to a nanometre). The interferometer also features a facility for detecting the lateral displacement of the beam in the measurement arm, providing feedback for the closed-loop stabilisation of the object mirror tilts that reduces the guidance-induced cosine error. With the series of test-run calibration of an optical ruler, we achieved the precision below 12 nm (k = 2) and accuracy below 34 nm (k = 2) over 25 mm range. A zero-drift test revealed the coincidence at a static position below 2,3 nm (k = 2) over six hours. Finally, the instrument is designed for automated operation with telemetry data collection compatible with the advanced manufacturing and Industry 4.0 demands.

Besides the environmental fluctuations, the typical sources of significant uncertainty in the laser interferometry systems are the geometrical errors. These are stemming, among others, from the misalignment of measurement axes, the thermo-mechanical influences of the system components and the mounting, guidance errors of the translation mechanism that carries the measurement mirror or vibrations. We report on a compact double-pass differential plane interferometer that features an original optical arrangement with four parallel and coplanar beams, where the beam pairs in the two arms are coaxial. The differential arrangement minimizes the dead path and shortens the metrological loop so that the sensitivity to thermal drifts and vibrations is reduced. The arm symmetry allows for the preservation of the Abbe principle, and the common path mitigates the influences of the environmental disturbances. The interferometer optics is designed as a self-contained single-piece assembly made using optical contacting from the low-expansion materials. The interferometer system integrates the homodyne receiver (even though the optical arrangement is well-suited for heterodyne detection too) and also a tilt-detection electronics that allows for detection of pitch and roll of the interferometer mirror so that the parasitic movement of the measuring mirror could be compensated for. The experimental characterization revealed a good optical performance of the interferometer with sub-nanometre cyclic error and the resolution of tilt detection in order of a few microradians.

in this paper, we present the preliminary results of a local magnetic field measurement at the position of 40 Ca + ion. We employ the simultaneous locking of the frequency of clock laser onto two transitions of Zeeman sublevels on transition 4s 2 S 1/2 (m=-1/2) − 3d 2 D 5/2 (m=-1/2 and -5/2). The frequency deviation from the spectral line center of both selected Zeeman transitions determines the magnetic field value on basis of the linear Zeeman shift thus one can estimate the clock frequency of the unperturbed 4s 2 S 1/2 − 3d 2 D 5/2 transition.

Precise time and/or stable optical frequency transfers over fiber are more and more deployed presently. Parallel transmission with telecommunication signals is often necessary, especially due to high intercity fiber rental costs. This parallel telecommunication traffic often exhaust both low loss transmission windows in single mode fibers (Conventional and Long, together 1530-1610 nm) where mature Erbium Doped Fiber Amplifiers are available. And very typically some additional spectral guard-bands are required. In our contribution we present results of fully bidirectional precise time transmission, over 1460 nm window with low attenuation penalty using modern fibers. Optical clock based on single calcium ion trapped into laser trap are being developed by different groups. Transition of interest for this optical clock corresponds to wavelength of 729 nm which can be down-converted into wavelength of 1458 nm without necessity of using an optical comb. In this paper, we experimentally verify time and radio frequency transmission using White Rabbit system operating in 1470 nm band over 200 km of standard single mode fiber and over more than 50 dB of attenuation using commercially available semiconductor optical amplifier.

Long-distance time and frequency transfer methods based on optical fibre links have evolved rapidly in recent years, demonstrating excellent performance for frequency transfer and considerable promise for accurate time transfer. CLONETS-DS is a European Union-funded research and innovation action intended to facilitate the vision of a sustainable, pan-European optical fibre network for precise time and frequency reference dissemination.

Atomic force microscopy (AFM) often relies on the assumption that cantilever bending can be described by simple beam theory and that the displacement of the tip can be evaluated from the cantilever angle. Some more advanced metrological instruments use free-space or fibre interferometers for measuring the position of the cantilever apex directly, thereby simplifying the metrology traceability chain. The next logical development, covering measurements of both the cantilever apex position and its deformation due to lateral forces acting during different AFM measurement regimes, is presented in this paper. It is based on using a set of closely packed fibre interferometers that can be used to determine localised bending of the cantilever at different positions along the cantilever. This can be used for detection of cantilever deformation beyond classical beam theory, and can yield both better understanding of sources of uncertainty in individual AFM force–distance measurements and more accurate scanning in constant height mode in high-speed AFM applications.

Animals are faced with a range of ecological constraints that shape their behavioural decisions. Habitat features that affect resource abundance will also have an impact, especially as regards spatial distribution, which will in turn affect associations between the animals. Here we utilised a network approach, using spatial and genetic data, to describe patterns in use of space (foraging sites) by free-ranging Egyptian fruit bats (Rousettus aegyptiacus) at the Dakhla Oasis in Egypt. We observed a decrease in home range size during spring, when food availability was lowest, which was reflected by differences in space sharing networks. Our data showed that when food was abundant, space sharing networks were less connected and more related individuals shared more foraging sites. In comparison, when food was scarce the bats had few possibilities to decide where and with whom to forage. Overall, both networks had high mean degree, suggesting communal knowledge of predictable food distribution.