Patent ID: 6934035

Claim:
A method of measuring an optical distance comprising the steps of: providing a first wavelength of coherence light and a second wavelength of light; directing light of the first wavelength and the second wavelength along both a first optical path and a second optical path, the first optical path extending onto a medium to be measured and the second path undergoing a change in path length; detecting light from the medium and light from the second optical path to measure a first change in phase of light interacting with the medium; adjusting the first wavelength of light to generate a third wavelength of low coherence light; directing light of the third wavelength and the second wavelength along both the first optical path and the second optical path, the first optical path extending onto the medium to be measured and the second path undergoing a change in path length; detecting light from the medium and light from the second optical path to measure a second change in phase of light interacting with the medium; superposing the first change in phase and the second change in phase to determine at least two phase crossing points; and determining the optical distance by counting the number of continuous interference fringes between the at least two phase crossing points.