TELECOMMUNICATION SYSTEMS

摘要

A telecommunication system has a laser-energised multi mode optical fibre 1. Data is input to the fibre by a series of modulators 4 each operating at a different subcarrier frequency. Optical radiation is detected by quadrant photodetector 3 which applies each of its outputs to respective channel sets. Each channel has a band pass filter 8 centred on a subcarrier frequency followed by a non-linear device 9. The signals from all the channels carrying the same subcarrier frequency are combined and the signals passed through band pass filters 11 centred on the second harmonic of the subcarrier frequency. Each of the modulators 4 consists of a plate bonded by a piezoelectric transducer and a pressure plate between which a length of optical fibre is sandwiched. When the transducer is energised the acoustic energy produced applies asymmetric radial strain to the fibre which induces radial or transverse birefringency, hence phase modulation of orthogonally polarised modes.