Enhanced waveguide metrology gauge collimator

An interferometric optical metrology gauge system, comprising:

• an interferometric device, said interferometric device further comprising:
• a planar lightwave circuit comprising a plurality of waveguide optical transmission elements embedded in a substrate, and
• an input coupler and an output coupler arranged along the optical transmission elements and operable to determine reference and measurement optical phases, wherein optical pathlengths of the optical transmission elements between the input coupler and the output coupler are matched to compensate for thermal effects;
• and
• a free-space optically-coupled collimator for the efficient bidirectional transmission of an optical metrology beam emanating from a waveguide aperture of one of the plurality of waveguide optical transmission elements,
• wherein the focus of the collimator is set at the waveguide aperture of the one of the plurality of waveguide optical transmission elements,
• wherein the optical axis of the collimator aligns with the optical metrology beam as it exits the waveguide aperture of the one of the plurality of waveguide optical transmission elements, and
• wherein the numeric aperture of the collimator is equal to or larger than the numeric aperture of the optical metrology beam as it exits the waveguide aperture of the one of the plurality of waveguide optical transmission elements.