Ondrej Havlis

Precise time transfer on the IPE - VUGKT line - a detailed analysis

We present implementation of a pilot bidirectional line IPE-VUGKT for precise time transmission. Directional non-reciprocities are evaluated together with uncertainties. Emphasis is given to the evaluation of the Sagnac effect. Our approach improves significantly the uncertainty.

Simultaneous transmission of distributed sensors and data signals

Nowadays, fiber-optic sensors are widely used in many areas of an industry. To confirm increasing interest in these sensors we performed a short survey of market analysis not only for recent years but also market prediction for a near future. We performed also a short survey of current trends in fiber-optic sensors based on latest published results. For special applications we designed two possible setups of simultaneous transmission of data and sensor signals in the same fibers. By measurement we have verified suitability of interferometric methods for sensor applications if fibers with active data transmissions are used. For back-scattered based sensors a high-power optical signal is necessary hence a measurement of dependence of pulse duration on intensity of the Brillouin peaks was performed.

Simultaneous transmission of the high-power phase sensitive OTDR, 100Gbps dual polarisation QPSK, accurate time/frequency, and their mutual interferences

Currently, fibre networks are only way how to satisfy the ever growing needs for more bandwidth. Thanks to that the optical fibre can be found almost anywhere and new applications and services can be transmitted through the networks. Accurate time transfer, ultra-stable frequency transfer and fibre-optic sensors networks have been rather common. High speed data transmission, time and frequency transmission, and fibre-optic sensors must share the common fibre-optic infrastructure because it would not be economically feasible to build separate fibre networks for long distances. Each system has individual transmission requirements and is prone to another type of interference. Data transmission systems based on DP-QPSK or DP-xQAM use digital signal processing for signal recovering but it cannot fully compensate signal degradation due to polarization dependent loss and nonlinear effects which are the most dominant sources of signal degradation. Accurate time signals are slow and often OOK modulated, therefore may experience the degrading effect of chromatic dispersion. Ultra-stable frequency signals are not modulated at all information transmitted is the frequency of photons and such signals are continuous wave, but they suffer from phase noise also environmentally introduced, e.g. by vibrations. For phase sensitive OTDR sensor systems the high power pulses are necessary to use which may cause interference with other signals. For this reason, parallel and simultaneous transmission in DWDM spectral grids of standard data, time, frequency, and sensing signals is rather new and unexplored area of research.

Simultaneous transmission of standard data, precise time, stable frequency and sensing signals and their possible interaction

Since optical fibre is a standard medium for all current and new networks, these optical networks offer possibility for connecting new applications over long distances almost to anywhere. However with increasing number of applications, the large number of dedicated fibres will be necessary. This constitution is quite unpractical in terms of costs, however since wavelength division multiplexing enables transmission of multiple different signals over one fibre it is more than suitable to use this technology for cost reduction and network efficiency increase. Wavelength division multiplexing technology is common in data networks where parameters of all signals may be optimized (especially maximum optical power launched into the fibre) for simultaneous transmission. In case of non-data applications the situation is more difficult because each application is connected by different type of signal and with its own requirements for transmission parameters. Hence it is necessary to evaluate possible interactions before field deployment. In this paper we deal with possible interaction of a coherent 100 Gb/s dual polarisation QPSK data signal with new applications like accurate time and stable frequency transmission and high-power pulse signal used for distributed sensing. In laboratory setup we performed a measurement with a standard G.652D single mode optical fibre and also with G.655 fibre which can also be found in some networks and may be source of more nonlinear interactions. All signals were transmitted in a grid with 100GHz spacing according to ITU standard. Results confirmed our assumptions that 100GHz spacing is not large enough and also that G.655 optical fibre is prone to more non-linear interactions.

Interference of Data Transmission in Access and Backbone Networks by High-Power Sensor System

ABSTRACT Currently, individual optical fibers are mostly used for each non-data application, which is very inefficient and uneconomical. Sharing a single fiber for multiple applications is a promising solution. However, in the case of a non-data application, the situation is much more complicated compared to data because of special application´s requirements. In laboratory setup, we performed a measurement with a standard G.652D optical fiber for analyzing possible interaction of stable frequency/accurate time transmission, 1.25/10Gbps data transmission (typical bitrates for access point-to-point networks), and high-power sensor signal for different channel spacing and different pulse duration of sensor signal.

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.

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.

Sensorie and data applications in national research and educational networks

High speed optical data networks are ubiquitous today. Data transmissions are based on coherent detection principles and use multilevel phase modulations. But another area of new applications is for example fiber-optic sensing. Such non-data signals present new challenges when designing networks. National research and educational network are at the forefront of such new developments.

Optical stabilization for time transfer infrastructure

In this paper, we propose and present verification of all-optical methods for stabilization of the end-to-end delay of an optical fiber link. These methods are verified for deployment within infrastructure for accurate time and stable frequency distribution, based on sharing of fibers with research and educational network carrying live data traffic. Methods range from path length control, through temperature conditioning method to transmit wavelength control. Attention is given to achieve continuous control for relatively broad range of delays. We summarize design rules for delay stabilization based on the character and the total delay jitter.

Resilience of semiconductor optical amplifier with holding beam injection to reflections in bidirectional reciprocal operation

We experimentally verified the resilience of the semiconductor optical amplifier with holding beam injection to reflections from transmission line in bidirectional operation over 200 km single fiber path together with influence of the temperature. The experiments show possible positive effects of such configurations with potential to improve bit error rate of transmitted signals.