A deflection sensor for a microcantilever includes two sets of interdigitated fingers, one (reference) set being attached to the substrate from which the microcantilever extends and the other (movable) set being attached to the tip of the microcantilever. Together the interdigitated fingers form an optical phase grating. The deflection of the microcantilever is measured by directing a light beam against the optical phase grating and detecting the intensity of the reflected light in the first (or other) component of the resulting diffraction pattern. As the microcantilever deflects, the reference and movable fingers move relative to one another creating large variations in the intensity of the zeroth and first order components of the diffraction pattern. To eliminate "1/f" noise the deflection of the microcantilever can be measured using an AC signal.