Patent ID: 7372577

Claim:
A metrology gauge for detecting a change in position of an object, comprising: a monolithic interferometer comprising: first optic for receiving a measurement beam and a reference beam, wherein the measurement beam and the reference beam are spatially distinct concentric beams; second optic bonded to said first optic; polarized beam splitter on an interface between said first and second optics, wherein the measurement and reference beams having a first polarization are transmitted from said first optic to said second optic through said polarized beam splitter; quarter-wave plate bonded to said second optic; a reference reflector bonded to said quarter-wave plate, wherein the reference beam is transmitted from said second optic to said reference reflector through said quarter-wave plate and is reflected by said reference reflector back to said second optic through said quarter-wave plate, wherein the measurement beam is transmitted from said second optic to a measurement reflector through said quarter-wave plate and through a non-reflective portion of said reference reflector and is reflected back to said second optic by the measurement reflector through the non-reflective portion of said reference reflector and said quarter-wave plate, wherein said polarized beam splitter deflects the reflected measurement and reference beams having a second polarization orthogonal to the first polarization; a third optic bonded to said second optic, said third optic for receiving a local oscillator beam; and a beam combiner on an interface between said second and third optics, said beam combiner for combining the local oscillator beam and the reflected measurement beam into a primary combined measurement and local oscillator beam and a redundant combined measurement and local oscillator beam, and for combining the local oscillator beam and the reflected reference beam into a primary combined reference and local oscillator beam and a redundant combined reference and local oscillator beam; and a redundant detector for receiving the redundant combined measurement and local oscillator beam and the redundant combined reference and local oscillator beam, and for detecting optical phase differences between the beams.