US 12,216,051 B2
Dynamic phase-shift interferometer utilizing a synchronous optical frequency-shift
James Millerd, Tucson, AZ (US)
Assigned to Onto Innovation Inc., Wilmington, MA (US)
Filed by Onto Innovation Inc., Wilmington, MA (US)
Filed on Jan. 21, 2022, as Appl. No. 17/581,534.
Prior Publication US 2023/0236125 A1, Jul. 27, 2023
Int. Cl. G01N 21/45 (2006.01); G01N 21/21 (2006.01)
CPC G01N 21/45 (2013.01) [G01N 21/21 (2013.01); G01N 2201/06113 (2013.01)] 22 Claims
OG exemplary drawing
 
1. An optical device for characterizing a test object, comprising:
a tunable light source that is controlled to generate input light having a time varying frequency;
a polarization frequency-shifting element that receives the input light and that is controlled to generate two beams that are orthogonally polarized and have respective frequencies that differ from each other by a first frequency shift;
one or more optical cavities that receive the two beams, the one or more optical cavities comprising a reference path and a test path that are traversed by the two beams to produce a pair of reference beams and a pair of test beams, wherein an optical path difference between the test path and the reference path induces a second frequency shift on the pair of test beams that is a function of a static length of the optical path difference, the pair of test beams differ from the pair of reference beams in frequency by the second frequency shift, wherein the first frequency shift is controlled by the polarization frequency-shifting element to have a pre-defined relationship with respect to the second frequency shift; and
a polarization phase sensor that receives the pair of reference beams combined with the pair of test beams and detects an interferogram produced by interference of a reference beam and test beam that are orthogonally polarized with respect to each other and that have frequency shift magnitudes with the pre-defined relationship.