Lensless user input device with optical interference based on diffraction with a small aperture

An optical navigation device which uses optical interference to generate navigation images. The optical navigation device includes an optical element, a light source, a sensor array, a navigation engine, and a light shield. The optical element includes a finger interface surface. The light source includes a laser in optical communication with the finger interface surface to provide light to the finger interface surface. The sensor array detects light reflected from the finger interface surface in response to contact between a finger and the finger interface surface. The navigation engine is coupled to the sensor array. The navigation engine generates lateral movement information based on lateral movement of the finger relative to the sensor array. The light shield is between the optical element and the sensor array. The light shield includes an aperture linearly aligned with the sensor array.