USER INPUT DEVICE WITH PLANAR LIGHT GUIDE ILLUMINATION PLATE

A user input device to generate an optical navigation signal based on an edge-lit pattern. The user input device includes an optical element, a light source, a sensor array, and a navigation engine. The optical element includes a finger interface surface. At least a portion of the optical element exhibits total internal reflection (TIR). The light source provides 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 contact between the finger and the finger interface surface disrupts the TIR and causes light to be reflected out of the optical element towards the sensor array. The navigation engine generates lateral movement information, which is indicative of lateral movement of the finger relative to the sensor array, in response to the detected light.