A method of detecting activation of a touch panel comprising: providing an N by M touch panel including a matrix of N rows of touch elements (22, 26, 28) along a first axis and M columns of touch elements (22, 26, 28) along a second axis; providing N optical beams, each of the N optical beams being provided by a respective source waveguide, the cross-sectional area of each of the source waveguides of the N optical beams being different to the cross-sectional area of each of the other source waveguides of the N optical beams such that a respective optical amplitude of each beam of the N beams is different than the corresponding optical amplitude of any other of the N optical beams, and such that the summation of an optical amplitude of any first group of the N optical beams is different than the summation of the corresponding optical amplitude of any other N beams, where each respective beam of the N optical beams corresponds to an input of each of the N rows; summing the optical amplitude from an output of each of the N rows; providing M optical beams, each of the M optical beams being provided by a respective source waveguide, the cross-sectional area of each of the source waveguides of the M optical beams being different to the cross-sectional area of each of the other source waveguides of the M optical beams such that a respective optical amplitude of each beam of the M beams is different than the corresponding optical amplitude of any other of the M optical beams, and such that the summation of an optical amplitude of any first group of the M optical beams is different than the summation of the corresponding optical amplitude of any other M beams, where each respective beam of the M optical beams corresponds to an input of each of the M columns; summing the optical amplitude from an output of each of the M columns; and unambiguously identifying a touch element (22, 26, 28) of the N rows and M columns of touch elements based upon the summation of the outputs. providing an N by M touch panel including a matrix of N rows of touch elements (22, 26, 28) along a first axis and M columns of touch elements (22, 26, 28) along a second axis; providing N optical beams, each of the N optical beams being provided by a respective source waveguide, the cross-sectional area of each of the source waveguides of the N optical beams being different to the cross-sectional area of each of the other source waveguides of the N optical beams such that a respective optical amplitude of each beam of the N beams is different than the corresponding optical amplitude of any other of the N optical beams, and such that the summation of an optical amplitude of any first group of the N optical beams is different than the summation of the corresponding optical amplitude of any other N beams, where each respective beam of the N optical beams corresponds to an input of each of the N rows; summing the optical amplitude from an output of each of the N rows; providing M optical beams, each of the M optical beams being provided by a respective source waveguide, the cross-sectional area of each of the source waveguides of the M optical beams being different to the cross-sectional area of each of the other source waveguides of the M optical beams such that a respective optical amplitude of each beam of the M beams is different than the corresponding optical amplitude of any other of the M optical beams, and such that the summation of an optical amplitude of any first group of the M optical beams is different than the summation of the corresponding optical amplitude of any other M beams, where each respective beam of the M optical beams corresponds to an input of each of the M columns; summing the optical amplitude from an output of each of the M columns; and unambiguously identifying a touch element (22, 26, 28) of the N rows and M columns of touch elements based upon the summation of the outputs.