Abstract: A wall shear stress sensor comprising first and second optical gratings, an incident light source and a photodetector. The second optical grating overlaps the first optical grating such that the first optical grating and second optical grating form a Moiré fringe pattern, wherein the second optical grating is displaceable relative to the first optical grating in response to a wall shear stress imparted on the sensor, and wherein displacement of the second optical grating correlates with a phase shift in the Moiré fringe pattern. The incident light source is configured to sequentially illuminate a plurality of discrete locations distributed across the Moiré fringe pattern. The photodetector is configured to detect light intensity reflected from each discrete location on the Moiré fringe pattern. A method of using the sensor and a two dimensional wall shear stress sensor system are also disclosed.