Intermode phase scanning for recovering phase-modulated signals on multimode optical fibres

Phase-modulated data transmission in multimode optical fibres is complicated by signal fades due to variations in intermodal phase. The letter describes a very simple technique to recover the data without the use of complex diversity receivers. The method involves varying the relative modal phases at a rate sufficient to ensure at least one signal maximum during each bit period. Thus the input signal is sampled and may be recovered by lowpass filtering. Experimental results demonstrate that the error rate for a single-channel digital receiver can be reduced by several orders of magnitude using this technique.