Birefringence and polarization fluctuations as a result of optical fibre bending during scanning of a KAT-7 riser cable

We evaluate the effects of optical fibre bending on polarization mode dispersion (PMD) and states of polarization (SOP) for a KAT-7 dish antenna riser cable. The antenna riser cable is the optical cable extending from the pedestal to the focus of the antenna. The riser cable for each antenna is subjected to environmental variations and to any physical variation caused by the motion of the fibre while the antenna is being scanned. To emulate this, we have investigated the effects of optical fibre bending with a riser cable inserted in a bending jig built to simulate antenna scanning movements. Measurements have shown that Differential Group Delay (DGD) values remain below 10 fs in the loop back configuration and below 6fs in the straight through configuration of the optical fibre placement in the bending jig. For the purpose of this paper, PMD and SOP measurements were made with a single varying element being the amount of bending enforced onto the optical fibres under test.