Active detection of propagation delay variations in single way time transfer utilizing dual wavelengths in an optical fiber network
Paper i proceeding, 2011

Several communication systems of today rely on the real time accessibility of accurate time and frequency measures and there is an increasing demand for the development of new and redundant methods for the distribution of these measures. The classical two-way method is able to compensate for the inevitable variations in the time and frequency propagation delay. The two-way method is used for time transfer in free space, electrical or optical domain, but has the disadvantage of often using two different paths for transmitting back and forward. The paths may be of equal length and have equal propagation delay, but nevertheless there is often a remaining asymmetry in the propagation paths. The inevitable asymmetry between the paths in the time transfer delay must be detected and compensated for, if an accuracy better than s-level is needed for transmission distance exceeding a few km. Furthermore, if the number of users is high, there will be a complex and large network of two-way time signal transmissions. Therefore, a solution using one-way broadcasting would be more desirable, and would be possible if the variations in transmission time could be estimated from the received data at the far (user) end. The one-way method uses only one path of transmission and is possible to implement in existing Wavelength Division Multiplexing-networks. Proof of concept and results of this one-way time transfer technique based on transmission of a repetitive signal, modulated on two lasers at different wavelengths 8 nm apart and transmitted through an optical fiber, has been presented previously. These data showed a strong correlation between a change in transfer time at one wavelength, and the transfer time difference for the signals at the two wavelengths. In this paper, the setup and the measurement results have been improved and new data is collected which shows improvement in the reliability and quality of this technique. The stability is improved through component analysis and minimizing error sources. The distance is improved from 38km to 160km.

Proof of concept

Free space

Two wavelength

Active detection

Transfer time

Dual wavelength

Fiber optic networks


Time signals

Communication systems

Component analysis

Multiplexing equipment

Time transfer techniques

Transmission time

Frequency measures

Error sources

Optical domains

Transmission distances

Strong correlation

Propagation delays

Large networks

Real time

Optical fibers

Real time systems

Optical communication

Optical fiber networks

Propagation paths

Measurement results

Time transfer

Wavelength division


Sven-Christian Ebenhag

Chalmers, Mikroteknologi och nanovetenskap (MC2), Fotonik

Per Olof E Hedekvist

Chalmers, Mikroteknologi och nanovetenskap (MC2), Fotonik

R. T. Kenneth Jaldehag

SP Technical Research Institute of Sweden

Proceedings of the IEEE International Frequency Control Symposium and Exposition



Elektroteknik och elektronik