Signal measurement apparatus and beam modulation apparatus used therein

A signal measurement apparatus, comprising:

• at least one body comprising a composition that is non-transmissive with respect to said incident beam, said body being rotatable about an axis perpendicular to a surface of said body, said body having a first set of features and at least a second set of features on said surface, said first set of features comprising one or more transmissive features with respect to said incident beam along a first radial path at a first radial distance from said axis, and said second set of features comprising a plurality of data storage features along a second radial path at a second radial distance from said axis;
• and
• at least one reference sensor disposed over a first position along said second radial path;
• at least one beam input device for sampling said modulated beam;
• and
• at least one digital signal processing device for calculating at least one of a magnitude and a phase of said signal component of said incident beam based on said modulated beam and a reference signal,
• wherein said first and said second radial distances are different, wherein a number of said transmissive features and a number of said plurality of data storage features are relatively prime, wherein said first set of features modulate said incident beam when said body is rotating, and wherein said reference sensor is configured for generating said reference signal based on at least a portion of said plurality of data storage features traversing said first position when said body is rotating.

A method of operating a signal measurement apparatus comprising at least one rotatable body having a first set of features traveling in a first radial path at a first radial distance for modulating an incident beam and at least a second set of features traveling in a second radial path at a second radial distance, at least one reference sensor disposed over a first position along said second radial path to generate a reference signal based on said second features and, at least one beam input device for sampling a modulated incident beam, the method comprising:

• rotating said body at a first frequency to generate a first modulated beam and a first reference signal;
• sampling a portion said first modulated beam at said beam input device based on said first reference signal;
• generating a modulation waveform based on said portion of first modulated beam and said first reference signal;
• rotating said body at a second frequency to generate a second modulated beam and a second reference signal;
• sampling a portion said second modulated beam at said beam input device based on said second reference signal;
• and
• computing a phase and magnitude of said second modulated signal based at least on said portion of said second modulated beam and said modulation waveform,
• wherein said first and said second radial distances are selected to be different, and wherein a number of said transmissive features and a number of said plurality of data storage features are selected to be relatively prime.