QUANTUM NON-DEMOLITION OPTICAL TAPPING

摘要

2066260 9104509 PCTABS00003 A single silica optical fibre (4) is formed into a Sagnac interferometer (2) by forming a fused, dichroic optical fibre coupler (8) having four ports (10, 12, 14 and 16). A 1.3.mu.m optical data signal is coupled to the port (10) via a dichroic optical fibre coupler (18) which combines it with a 1.53.mu.m c-w probe signal from laser (16). The coupler (8) splits the 1.53.mu.m probe signal into two equal intensity, counter-propagating portions and couples the 1.3.mu.m data signal so it propagates in one direction round the loop (6). The loop (6) exhibits a non-linearity such that the data signal provides a relative phase shift of the counter-propagating c-w probe portions causing a portion of the 1.53.mu.m signal is switched to port (12). This 1.53.mu.m switched output provides tapping of the data signal without affecting its intensity.