A system for interrogating an optical sensing fiber comprising a multimode core, the system comprising: multiple interferometers including multiple reference branches and multiple measurement branches, the multiple measurement branches comprising an array of single-core, single-mode optical fibers, each optical fiber of the array of single-core, single-mode optical fibers having a different optical delay; a tunable laser configured to generate laser light over a range of wavelengths, the laser light configured to be coupled into the multiple reference branches and the multiple measurement branches for interferometrically probing the multimode core; and a micro lens array and collimator lens configured to optically couple the laser light from the array of single-core, single-mode optical fibers into the multimode core, and configured to image backward traveling multimode light from the multimode core onto the array of single-core, single-mode optical fibers, wherein light from each mode of the backward traveling multimode light is directed into a corresponding fiber of the single-core, single-mode optical fibers; acquisition circuitry comprising multiple detectors configured to detect measurement interferometric data at an output of the multiple interferometers, the measurement interferometric data corresponding to reference light combined with the backward traveling multimode light directed into the array of single-core, single-mode optical fibers; and data processing circuitry configured to: determine coupling coefficients from the measurement interferometric data, the coupling coefficients being between light input from the array of single-core, single-mode optical fibers into the multimode core and light output from the multimode core to the array of single-core, single-mode optical fibers; and determine, from the coupling coefficients, cross-coupling coefficients between forward traveling modes in the multimode core and backward traveling modes in the multimode core. multiple interferometers including multiple reference branches and multiple measurement branches, the multiple measurement branches comprising an array of single-core, single-mode optical fibers, each optical fiber of the array of single-core, single-mode optical fibers having a different optical delay; a tunable laser configured to generate laser light over a range of wavelengths, the laser light configured to be coupled into the multiple reference branches and the multiple measurement branches for interferometrically probing the multimode core; and a micro lens array and collimator lens configured to optically couple the laser light from the array of single-core, single-mode optical fibers into the multimode core, and configured to image backward traveling multimode light from the multimode core onto the array of single-core, single-mode optical fibers, wherein light from each mode of the backward traveling multimode light is directed into a corresponding fiber of the single-core, single-mode optical fibers; acquisition circuitry comprising multiple detectors configured to detect measurement interferometric data at an output of the multiple interferometers, the measurement interferometric data corresponding to reference light combined with the backward traveling multimode light directed into the array of single-core, single-mode optical fibers; and data processing circuitry configured to: determine coupling coefficients from the measurement interferometric data, the coupling coefficients being between light input from the array of single-core, single-mode optical fibers into the multimode core and light output from the multimode core to the array of single-core, single-mode optical fibers; and determine, from the coupling coefficients, cross-coupling coefficients between forward traveling modes in the multimode core and backward traveling modes in the multimode core. determine coupling coefficients from the measurement interferometric data, the coupling coefficients being between light input from the array of single-core, single-mode optical fibers into the multimode core and light output from the multimode core to the array of single-core, single-mode optical fibers; and determine, from the coupling coefficients, cross-coupling coefficients between forward traveling modes in the multimode core and backward traveling modes in the multimode core.