A signal interrogation system comprising: 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 having on one side a single channel end and on another side multiple channel ends with multiple switchable channels, the bi-directional optical switch being disposed in the second path, with the single channel end oriented toward the optical circulator; a plurality of optical fibers coupled to the multiple channel ends of the bi-directional optical switch, wherein the bi-directional optical switch is arranged to switch the second laser beam among the plurality of optical fibers coupled to the multiple switchable channels, the plurality of optical fibers being arranged to direct the second laser beam to a target and receive interference optical signals based on reflection/scattering lights of the second laser beam from the target; an interference optical signals path coupled to the optical circulator to receive the interference optical signals from the bi-directional switch; a balanced photo detector to measure a power difference between the interference optical signals and the power reference, a variable optical attenuator disposed in the first path between the optical coupler and the photo detector, the variable optical attenuator being arranged to receive on one side the power reference from the optical coupler and to convey from another side the power reference to the balanced photo detector; and a computer coupled to the balanced photo detector to receive the measured power difference, and coupled to the variable optical attenuator to control the variable optical attenuator to match power of the first laser beam as the power reference and the interference optical signals directed to the balanced photo detector. 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 having on one side a single channel end and on another side multiple channel ends with multiple switchable channels, the bi-directional optical switch being disposed in the second path, with the single channel end oriented toward the optical circulator; a plurality of optical fibers coupled to the multiple channel ends of the bi-directional optical switch, wherein the bi-directional optical switch is arranged to switch the second laser beam among the plurality of optical fibers coupled to the multiple switchable channels, the plurality of optical fibers being arranged to direct the second laser beam to a target and receive interference optical signals based on reflection/scattering lights of the second laser beam from the target; an interference optical signals path coupled to the optical circulator to receive the interference optical signals from the bi-directional switch; a balanced photo detector to measure a power difference between the interference optical signals and the power reference, a variable optical attenuator disposed in the first path between the optical coupler and the photo detector, the variable optical attenuator being arranged to receive on one side the power reference from the optical coupler and to convey from another side the power reference to the balanced photo detector; and a computer coupled to the balanced photo detector to receive the measured power difference, and coupled to the variable optical attenuator to control the variable optical attenuator to match power of the first laser beam as the power reference and the interference optical signals directed to the balanced photo detector.