US 12,359,972 B2
Three phase spectral interferometry
Ryan Douglas Muir, Livermore, CA (US); John E. Heebner, San Ramon, CA (US); and Daniel Ernest Mittelberger, Livermore, CA (US)
Assigned to Lawrence Livermore National Security, LLC, Livermore, CA (US)
Filed by Lawrence Livermore National Security, LLC, Livermore, CA (US)
Filed on Oct. 17, 2022, as Appl. No. 18/047,120.
Prior Publication US 2024/0133743 A1, Apr. 25, 2024
Int. Cl. G01J 3/45 (2006.01); G01J 3/02 (2006.01); G01J 3/28 (2006.01); G01J 11/00 (2006.01)
CPC G01J 3/45 (2013.01) [G01J 3/0205 (2013.01); G01J 3/2823 (2013.01); G01J 11/00 (2013.01)] 23 Claims
OG exemplary drawing
 
1. An interferometric method for determining characteristics of an input optical signal using a three-phase interferometric system, comprising:
providing the input optical signal to a first input of a three-by-three optical splitter;
providing a reference optical signal to a second input of the three-by-three optical splitter, wherein one or more of spectral characteristics of the reference optical signal is unknown, wherein a third input of the three-by-three optical splitter is unused;
measuring spectra associated with three interferograms produced at a first, a second and a third output of the three-by-three optical splitter, respectively, wherein each interferogram corresponds to an optical output signal that has a relative phase shift of substantially 120 degrees with respect to any of the other output optical signals of the three-by-three optical splitter; and
determining an amplitude value and a phase value of the input optical signal from information obtained from measured spectra, wherein the interferometric method comprises, prior to providing the input optical signal and the reference optical signal for determining characteristics of the input optical signal, performing an alignment procedure comprising:
(a) blocking a path of the reference optical signal and allowing the input optical signal to reach the three-by-three splitter,
(b) without using an input polarizer in a path of the input optical signal, coarsely aligning the output polarizers positioned at the three outputs of the three-by-three splitter to within about 10° of a slow axis of the three-by-three splitter,
(c) iterating between a rotation angle of the output polarizers and an input polarization controller until interference fringes are minimized,
(d) placing the input polarizer in the path of the input optical signal and aligning the input polarizer to obtain a desired throughput, and
(e) repeating operations (c) through (d) for the reference optical signal while blocking the input optical signal, while placing a corresponding input polarizer in a path of the reference optical signal in operation (d).