A signal interrogation system comprises an optical coupler to split input laser beam into a first laser beam as a power reference and a second laser beam, the optical coupler being coupled to a first path for the first laser beam and a second path for the second laser beam an optical circulator disposed in the second path a bi-directional optical switch disposed in the second path and having on one side a single channel end oriented toward the optical circulator and on another side multiple channel ends with multiple switchable channels a plurality of optical fibers coupled to the multiple channel ends of the bi-directional optical switch an interference optical signals path coupled to the optical circulator to receive the interference optical signals from the bi-directional switch and a balanced photo detector to measure a power difference between the interference optical signals and the power reference.
