A measurement of propagation delay

A measurement method and associated uncertainty analysis have been developed for the measurement of propagation or group delay in electrical transmission lines and optical fibres. The measurement method and uncertainty analysis were applied to measurements of optical fibre delay lines that introduce tens of microseconds of delay (1 km, 2 km and 4 km fibre lengths) and trombone lines that introduce sub-nanosecond delays. For the measurement method described here, uncertainties in the measured delay are as low as 90 fs (95% confidence interval) for a propagation delay of 660 ps and less than 200 ps (95% confidence interval) for a propagation delay of 20 µs.