Patent ID: 7057735

Claim:
A method for determining the absolute physical thickness of an optically transparent object of unknown refractive index, the method comprising the steps of: transmitting a first broadband optical signal across an optically transparent object in the direction associated with a parameter to be measured; capturing a first pair of reflected signals from said optically transparent object, a first signal of said first pair associated with a near surface reflection of said object and a second signal of said first pair associated with a far surface reflection of said object; transmitting a second broadband optical signal across the optically transparent object in opposition to said first broadband optical signal; capturing a second pair of reflected signals from said optically transparent object, a first signal of said second pair associated with a near surface reflection of said object and a second signal of said second pair associated with a far surface reflection of said object; determining a separation between said first pair of reflected signals and said second pair of reflected signals by comparing the signals in the spectral domain to determine a beat frequency to determine the absolute physical thickness of the optically transparent object.