Speaker
Description
We examine the suitability of White Rabbit for the distribution of a reference phase signal in radio interferometers. Receptors in an interferometric array require a stable reference phase, and the phase noise due to the clock distribution could possibly lead to a reduction in the amplitude of the cross product of the signals, an effect known as 'coherence loss', which reduces the sensitivity of the observation.
We develop a method to predict the coherence loss from the measurements of the ADEV and MDEV, including a novel expression for the coherence loss due to flicker phase modulation.
We introduce a new method to calibrate the dispersion parameter alpha, which is especially convenient on already deployed fiber. By using two independent strands of the same fiber cable between two White Rabbit switches, with their wavelengths swapped, we can directly measure the dispersion on the fiber, assuming both links have the same average value. This is achieved by having both links operating simultaneously, which requires only a modification of the firmware. Notably, this method requires no other external parts such as time interval counters or oscilloscopes, and can continuously monitor the dispersion value.
We show how to make a White Rabbit signal co-exist with existing fiber infrastructure that is already in operation with operational traffic on a DWDM network. Our method uses two wavelengths outside of the optical C-band for the counter-propagating White Rabbit signals on a single fiber, and uses bi-directional silicon based optical amplifiers instead of erbium doped fiber amplifiers. This ensures that the requirement of having both directions of the link on the same fiber can still be met, and allows for complete calibration of the link.
Finally, we bring all these methods together by connecting two radio telescopes in the Netherlands, and successfully perform very long baseline interferometry observations using White Rabbit as a phase reference and time distribution method.
