Two color one-way frequency transfer in an urban optical fiber network

SP Technical Research Institute of Sweden has previously presented results with a two color one-way method. This method is an alternative method to two-way time and frequency transfer that is useful if there are unknown asymmetries in the connection. The method is possible to use in existing infrastructure and is able to coexist with data channels for example in WDM systems, which make it possible to broadcast to multiple users and enables the user to be anonymous to the time or frequency transfer. This paper will present the results from the analysis when implementing the technique in an urban commercial optical fiber data communication WDM network between two clock labs in Sweden connecting two cesium clocks to each other for frequency comparison. The evaluation is performed with two wavelengths 8 nm apart on 6 km of installed fiber in an urban city network. The transmitter and the receiver are installed in an electromagnetically shielded room several meters below ground, and the fiber runs to a building at a distance of 3 km, and then back again. The comparison will be within the laboratory, eliminating any errors from a reference system. Results and conclusion from this evaluation reveals the propagation delay variations in the propagation distance and will display the need of compensation for these variations.