Patent ID: 7289220

Claim:
A method for determining an optical path length (OPL) of an optical cavity comprising the steps of: a) impinging a light beam from a broadband coherent light source on the optical cavity thereby forming a modulated light beam by optical interference; b) directing the modulated light beam from the optical cavity to a light dispersive element thereby splitting the modulated light beam into a spectrum of component light frequencies each having a light intensity and a corresponding light wavelength; c) detecting the component light frequencies in a light detector thereby generating spectral data with dimensions of light intensity of the component light frequencies as a function of the wavelength of the component light frequencies; and d) processing the spectral data by performing a mathematical Fourier transform of the spectral data using a Fourier transform algorithm, thereby generating a transform spectrum with a Fourier amplitude as a function of an independent length variable, wherein the transform spectrum has a peak corresponding to a non-changing (DC) component of the spectral data, and at least one modulation peak located at a coordinate of the length variable corresponding to twice the OPL of the optical cavity.