An optical sensor measures displacement of a haptic plate that provides haptic sensation to a user. The optical sensor comprises a light source, a plurality of optical detectors, and a controller. The light source is configured to illuminate a surface of the haptic plate in which a haptic wave propagates causing displacement of portions of the haptic plate in one or more directions. The plurality of optical detectors is configured to detect light reflected from the surface of the haptic plate. At least two optical detectors of the plurality of optical detectors are positioned relative to the light source such that an amount of light received at each of the optical detectors is based at least in part on a direction of displacement of the haptic plate. The controller is configured to monitor the haptic wave using the detected light from the plurality of optical detectors.