Method of measuring relative movement in two dimensions of an object and an optical input device using a single self-mixing laser

An optical module for performing a method of determining movement and/or distance of an input device and object relative to each other along a measuring axis transverse to an action plane, the module comprising a laser device having a laser cavity, means for supplying a modulated drive current to said laser device and illuminating an object surface with a measuring laser beam emitted from the laser cavity of said laser device, detector means for generating a measurement signal representative of changes in operation of the laser cavity, said changes being due to laser self-mixing interference of measuring beam radiation re-entering said laser cavity and an optical wave in said laser cavity and being representative of said relative movement and/or distance along said measuring axis, and said measurement signal including a rising portion and a falling portion in each period thereof on which is superposed undulations having an offset frequency, the module further comprising electronic processing means for determining distance and/or movement of said object and said input device relative to each other along said measuring axis by summing said offset frequency of a rising portion and a falling portion of said measurement signal, and generating an electric signal representative of said distance and/or movement.