Polarisation controller for fibre=optic transmission system - uses circularly polarised light in fibre, to avoid perturbation, for subsequent polarisation of predetermined type

摘要

The transmission system allows the control of the state of polarisation of the light beam. The optical fibre used has a controlled amount of torsion. An input allows light fed into the fibre to pass from one state of polarisation into a beam of light which is circularly polarised. The output at the second end of the fibre allows the light with circular polarisation to change into a beam with predetermined polarisation which is stable. The circularly polarised light travels through the fibre without perturbation as a result of the torsion in the fibre. The degree of torsion in the fibre is between one and ten turns per metre length of fibre. Two quarter wave plates are situated in the path of the beam at the input and output respectively. The system is used for transmitting data from physical parameters sensors.