Alma and E-merlin Data Transmission Systems: Lessons for Ska

ALMA, EVLA and e-MERLIN use high data rate optical fibre links based on commercially available 10 Gbps opto-electronics. This paper describes the systems designed by NRAO and JBO staff to be used in ALMA and e-MERLIN. ALMA has a requirement for a 120 Gbps data rate per telescope, requiring the use of 12 lasers in the 1550 nm telecommunication band, with maximum link lengths around 20 km. e-MERLIN has a lower bandwidth and requires 30 Gbps links per telescope and therefore three lasers per telescope; however, the link lengths reach up to around 400 km, and amplification, de-dispersion and regeneration are required. Dense wavelength division multiplexing is used to avoid fibre management problems and save fibre costs. The design criteria and experience gained in these projects is very relevant to SKA as the proposed configuration of the antenna elements maps well to the link lengths used here. The chosen data rate will be a major cost driver.