INTERFEROMETER COUPLER USING MULTIPLE INPUT PORTS FOR IMPROVED STABIBLITY

摘要

A multiport bidirectional coupler (31) is interconnected to a two beam interferometer (30), such as a Sagnac interferometer. Light from a source (40) is input into each of the ports (32-34) of the coupler (31) in turn. For each input the corresponding output intensities from all ports (32-34) are each mesured by a detector (39). By optical reciprocity, cyclic sums formed from the measured output allow an accurate estimation of the phase shift of the interferometer (30) independently of small deviations of the coupler parameters from ideal values. Thus instabilities of the coupler (31), due for example to age or temperature, are compensated for. A single pulse from the source (40) can be used to sequentially interrogate the interferometer (30) through each of the ports (32-34) in turn, by using additional couplers (35-38) and delay loops (41-44) to temporally stream the input and output signals.