Precise and Secure Time Dissemination Through White Rabbit Network Based Optical Fibre Link

Precise transfer of time and frequency signals is an indispensable activity in the field of time and frequency metrology. Accurate time is a critical requirement for various fields, e.g., navigation, telecommunication and finance sectors along with many technological applications and advanced scientific research. Satellite based time transfer methods fulfil the requirements of accurate time for most of these applications but vulnerability to jamming and spoofing of satellite signals are big concerns for many of the critical applications. Optical fibre-based time transfer techniques provide excellent options for transferring precise and secure time over a distance of several hundreds of kilometers. The present work describes the establishment of an optical fibre link at CSIR-National Physical Laboratory, India utilising White Rabbit Precision Time Protocol (WR-PTP) for precise and accurate transfer of time and frequency signals from a reference atomic clock. White Rabbit (WR) technique includes several advanced features, e.g., synchronous ethernet, precision time protocol, digital dual mixer time difference etc. for measuring as well as compensating link delays very accurately and provides time synchronisation within sub-nanosecond uncertainty. In order to enhance the accuracy and stability of the optical fibre link, a feedback loop has been utilised for estimating as well as compensating dynamic phase variation, which arises due to ambient temperature variation around the link.