Multimode optical fibre phase modulators and discriminators: II--Experiments

Low-moded coherent optical fibre systems are very microphonic. Any mechanical stress applied to the fibre causes phase modulation of the guided optical carrier, which is then converted to a related amplitude modulation by a fibredyne (fibre optic self-homodyne) detection process at the photodiode. In a companion letter, a simple theory was published which described the causes and characteristics of three p.m. to a.m. discriminator effects in multimode fibredyne systems. Experimental evidence for the two predominant p.m. to a.m. phenomena is presented and compared with the theory.