Simon Rerucha

Detection of Interference Phase by Digital Computation of Quadrature Signals in Homodyne Laser Interferometry

We have proposed an approach to the interference phase extraction in the homodyne laser interferometry. The method employs a series of computational steps to reconstruct the signals for quadrature detection from an interference signal from a non-polarising interferometer sampled by a simple photodetector. The complexity trade-off is the use of laser beam with frequency modulation capability. It is analytically derived and its validity and performance is experimentally verified. The method has proven to be a feasible alternative for the traditional homodyne detection since it performs with comparable accuracy, especially where the optical setup complexity is principal issue and the modulation of laser beam is not a heavy burden (e.g., in multi-axis sensor or laser diode based systems).

Joint accurate time and stable frequency distribution infrastructure sharing fiber footprint with research network

Abstract. The infrastructure essentialities for accurate time and stable frequency distribution are presented. Our solution is based on sharing fibers for a research and educational network carrying live data traffic with time and frequency transfer in parallel. Accurate time and stable frequency transmission uses mainly dark channels amplified by dedicated bidirectional amplifiers with the same propagation path for both directions of transmission. This paper targets challenges related to bidirectional transmission, particularly, directional nonreciprocities.

Transfer of stable optical frequency for sensory networks via 306 km optical fiber link

Optical fiber links for distribution of highly-stable optical frequencies were experimentally tested by many metrology laboratories in the past fifteen years. But recent development of new optical sensors for industrial application puts demands on a technology transfer of this high-end technology from laboratory experiments to the real industry. The remote calibration of interrogators of Fiber Bragg Grating strain sensory networks is one of important examples. We present a 306 km long optical fiber link established in the Czech Republic where a coherent transfer of stable optical frequency has been firstly demonstrated. The link between ISI CAS Brno and CESNET Prague uses an internet communication fiber where a window 1540 to 1546 nm in DWDM grid is dedicated for the coherent transfer and 1 PPS signal. The optical frequency standard at 1540.5 nm is used for the coherent transfer where compensation of the Doppler shift induced by the optical fiber is done by an acousto-optic modulator driven by a servo loop. The closed loop action is continuously recorded. This enables to compute changes in the transport delay introduced by external influences on the optical line. A comparison with a different measuring method based on analyzing the transport delay of a 1 PPS signal transmitted via the same DWDM window is done. This comparison is a subject of results of the paper.

Joint stable optical frequency and precise time transfer over 406 km of shared fiber lines — Study

We present a preliminary study of bidirectional ultra-stable optical frequency and precise time transmission over 406 km long path in the telecom-grade fiber optic infrastructure of dense wavelength division multiplexing. The main challenge in this application is the need of bidirectional amplification to compensate for signal loss. Directional non-reciprocities of the time transfer are evaluated together with their uncertainties. Solutions are proposed to significantly limit the final uncertainty.

Autocorrelation analysis of plasma plume light emissions in deep penetration laser welding of steel

The light emissions of the plasma plume in the deep penetration laser welding of metals typically have the character of irregular short-time pulses. Their nature indicates that the size of the plume significantly fluctuates and the plasma flows out of the keyhole in the form of short bursts rather than a continuous flow. In this paper, the authors study the plasma plume light emissions using an autocorrelation analysis. The authors show that it is an efficient tool for the detection of the plasma bursts period which is typically in the order of milliseconds. The authors compare the autocorrelation characteristics and the geometry of the welds made on a 2 kW ytterbium-doped yttrium aluminium garnet (Yb:YAG) fiber laser welding machine for the X5CrNi 18-10 stainless steel and the S235JR carbon steel. The welding parameters settings is varied over a range of laser power (1–2 kW) and welding speed (10–30 mm/s) usually used in industry. As a result, the authors identify a linear dependence between the plasma b...

Computational approach to phase detection in frequency-modulation interferometry

We present a new approach to the interference phase detection in the frequency-modulation interferometry. Using a frequency-tunable laser beam and several computational steps we show that the interference phase can be detected with a sub-nanometer resolution from a single interference signal coming from a non-polarizing interferometer sampled by a single photo-detector. This represents significant simplification of the necessary optical setup in comparison to the conventional homodyne interferometry that requires several polarizing optical elements to produce two interference signals in quadrature. The experimental results show that our method achieves comparable accuracy as the homodyne detection which makes it usable in applications where the interferometric setup simplicity is necessary.

Light source for low-coherence interferometry surface diagnostics

We describe in this paper a pilot experiment of optimization of a white-light source for a low-coherence interferometry. The white-light source combines the light beams generated with colour LEDs. By modelling of the white light spectra, a contrast of a white light interference fringe could be changed and set to the maximal value. The second part of this paper is a description of a white-light fringe analysis ensured with a low-cost colour CCD camera. The used detection technique employs a phase-crossing algorithm which identifies a zero optical path difference as the point where the phase difference between the red, green and blue part of the white-light interference fringe becomes equal to zero. The optimized white light source is designed to be a crucial part of an experimental setup for the surface diagnostics and automatic calibration of gauge blocks.

Multi-purpose infrastructure for dissemination of precise stable optical frequency

Long distance precise frequency and accurate time transfer methods based on optical fiber links have evolved rapidly in recent years, demonstrating excellent performance. They are attractive both for very high-performance applications and as a secure alternative complement to radio- and satellite-based methods. In this paper, we present development of infrastructure for such transmission containing 700+km of transmission lines, with planned cross border optical frequency connectivity. According to our knowledge, this will be the third such line globally. The infrastructure also shares fibers with existing data transmissions, both amplitude and phase modulated, which poses high demands on mutual isolation and insensitivity to cross talks.

Miniaturized GPS position logger for tracking of small mammals

The satellite tracking of animal individuals remains a signiücant source of knowledge in the area of zoology. The greatest limitation is the size and weight of the satellite position loggers that prevents the usage of satellite telemetry on three-fourths of mammal and bird species. We present an architecture and design of a miniaturized GPS logger with the weight below ten grams that would be suitable for the studies targeting demanding study groups such as the only European flying fox. Our design combines the GPS logging with traditional telemetry signaling, typically used for manual radio tracking, allows for radio-transmitted position data retrieval and the 2–3 days of battery life. The performance has been verified within a field testing.

CLONETS - clock network services: Strategy and innovation for clock services over optical-fibre networks

Methods for long-distance time and frequency transfer over optical fibers have demonstrated excellent performances and are evolving rapidly. CLONETS is a European Union-funded coordination and support action intended to facilitate the vision of a sustainable, pan-European optical fiber network for precise time and frequency reference dissemination.