Low-cost monitoring of the wavelength difference of two transmitters for two-way time transfer over optical fibre

Accurate time transfer is routinely performed using GPS, however an order of magnitude better accuracy can be achieved when signal transfer over optical fibres is used (e.g., in [1], fibre transfer over 73 km with <100 ps precision was achieved as compared to <700 ps for the GPS-based system). Unfortunately, the propagation delay through an optical fibre changes due to temperature variation. This is commonly compensated for by transferring the time information bi-directionally over a single optical fibre with subsequent cancellation of the propagation delay variations [1]. However, to avoid any signal degradation due to Rayleigh back-scattering and reflections at fibre connectors, it would be advantageous to transmit the information in both directions using different wavelength, each of them in a unidirectional sense [2]. However, this requires two transmitters operating at different wavelengths. Due to the limited stability of (low-cost) telecom-grade transmitters (generally ±0.1nm [3]), the propagation delay in both directions can change in an uncorrelated manner and thus could not be compensated by a known stable difference, degrading the precision of the time transfer

Low-cost Precise QoS Measurement Tool

Abstract—When implementing networks with QoS guarantees, precise measurement of network QoS characteristics is needed. Primary characteristics of this class are packet loss, throughput, delay, delay variation as well as distribution of delay and delay variation. Commercial network analyzers are often very expensive, do not include provisions for precise time synchronization needed for one-way delay measurement and are closed in a sense that it is not possible to integrate them with other applications for measurement result processing. In this article we describe an architecture and implementation of a simple low-cost measurement tool that can be used for precise measurements of all of the above listed characteristics in small laboratories

Precise Measurement of One-Way Delay and Analysis of Synchronization Issues

When implementing networks with QoS guarantees, precise measurement of all network QoS characteristics is necessary. We need to observe behaviour of various traffic handling mechanisms on different patterns of data, for example, to see influenc

Alternative spectral window for precise time fiber based transport

Precise time and also stable frequency transfers are approaching the state to become almost standard applications for optical fiber networks, especially they are becoming supported in multiple research and education networks. In principle, the time and frequency transfers are not possible to be implemented over data transport layer, which hasn't been was designed for essential stability, and thus dedicated wave band is required for such implementation. To achieve even better stability for precise time and stable frequency, the bidirectional transmission in single physical medium (fibers and ideally all components along the route) is preferred. The White Rabbit system combines synchronous Ethernet and Precise Time Protocol (IEEE-1588) and it has been designed in the CERN with the aim to provide time synchronization among large number of sensors, actuators and other devices utilized in experiments. Primary aim was the operation over single fiber (to avoid nonreciprocal changes in directions) using standard telecommunication transceivers designed for single fiber operation with reach limited to about 40 km. In this paper, we experimentally verify and compare stability of White Rabbit system operation over long distances up to 300 km using active optical amplification on wavelengths which should not be utilized within spectrum needed for regular data transmissions.</p

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

Alternative spectral windows for photonic services distribution

Optical fibers are becoming commonly used beside data transmissions for dissemination of ultra-precise and stable quantities or alternatively as distributed sensors of for example acoustic and mechanic vibrations, seismic waves, temperature etc. There have been developed methods for these transfers and their stabilization, allowing thus to achieve excellent performances. Such performance is bound with utilization of single physical medium for both ways of propagation. These methods are attractive both for very high-performance applications and as a secure alternative complementary to radio and satellite-based transfer methods. From economical point of view, sharing fibers with regular data traffic is an advantage, especially for longer distances and large infrastructures. Unfortunately, the most often used wavelengths are located almost in the middle of telecommunication band. Due to continuous data traffic growth and utilization of flexible spectral allocation, the collision in wavelength plan will occur more and more often. In this paper we overview alternative wavelengths suitable for these transfers, we also propose suitable methods for all-optical reach extension, by all-optical amplification. Shared line design allowing transfer of ultra-stable quantities in three different spectral bands is proposed and such design is evaluated.</p