A low coherence light source is used to generate a time-varying and space-localized interference pattern to excite oxygen-sensitive dye embedded in a polymer matrix inside an elongated channel waveguide. The sensing mechanism may be based on triplet-state and phosphorescence quenching of the photosensitizer dye by oxygen molecules. Phosphorescence emission resulting from the time-varying, space-localized excitation light is collected. The intensity or frequency of an oscillating component of the phosphorescence signal is used to quantify the local value of pO2 at a plurality of active measurement points along the waveguide. An oxygen sensor including the waveguide may be formed along a long axis of a needle so that a depth-resolved profile of pO2 in tissue is obtained.
