Patent ID: 8279446

Claim:
An apparatus for measuring a layered object, the apparatus comprising: a) a reference arm of an interferometer, the reference arm comprising a first section of polarization maintaining optical fiber engaged with a first fiber stretcher and terminating proximate to a first mirror; b) a measurement arm of the interferometer, the measurement arm comprising a second section of polarization maintaining optical fiber engaged with a second fiber stretcher and terminating at a first port of a first polarization selective light splitter and combiner configured to direct light of a first polarization through a second port to the layered object, and to direct light of a second polarization through a third port to a second mirror; c) a low coherence light source emitting low coherence light through a first polarization controller, into a first port and out of a second port of a second polarization selective light splitter and combiner, through a polarization maintaining fiber coupler and into the first and second sections of polarization maintaining optical fiber; and d) a coherent light source emitting coherent light through a second polarization controller, into a third port and out of the second port of the second polarization selective light splitter and combiner, through the polarization maintaining fiber coupler and into the first and second sections of polarization maintaining optical fiber; wherein the first polarization controller polarizes the low coherence light with the first polarization, and the second polarization controller polarizes the coherent light with the second polarization orthogonal to the first polarization; and wherein the low coherence light of the first polarization and the coherent light of the second polarization co-propagate through the reference arm of the interferometer and are reflected by the first mirror through the reference arm back to the polarization maintaining fiber coupler; and wherein the low coherence light of the first polarization and the coherent light of the second polarization co-propagate through the measurement arm of the interferometer, the coherent light of the second polarization is split from the low coherence light of the first polarization and reflects off the second mirror through the measurement arm back to the polarization maintaining fiber coupler, and the low coherence light of the first polarization is reflectable off the layered object through the measurement arm back to the polarization maintaining fiber coupler; and wherein back reflected low coherence light of the first polarization is propagated from the polarization maintaining fiber coupler to a first detector, and reflected coherent light of the second polarization is propagated from the polarization maintaining fiber coupler to a second detector.