A metrology system comprises a radiation source, an optical element, first and second detectors, an integrated optical device comprising a multimode waveguide, and a processor. The radiation source generates radiation. The optical element directs radiation toward a target to generate scattered radiation from the target. The first detector receives a first portion of the scattered radiation and generates a first detection signal based on the received first portion. The multimode waveguide interferes a second portion of the scattered radiation using modes of the multimode waveguide. The second detector receives the interfered second portion and generates a second detection signal based on the received interfered second portion. The processor receives the first and second detection signals. The processor analyzes the received first portion, the received interfered second portion, and a propagation property of the multimode waveguide. The processor determines the property of the target based on the analysis.