Optical comb-based interferometry with sinusoidal phase modulation for full-field surface profile and tomographic measurement

Optical‑frequency‑comb‑based metrology has rapidly advanced, enabling high‑precision and high‑speed measurements in ranging, spectroscopy, and interferometry. Building on these developments, we previously developed a microscopic interferometry using a 10‑GHz electro‑optic comb broadened by nonlinear effects, enabling high‑accuracy 3D profiling over several hundred micrometers to several millimeters without mechanical scanning and with electronically controlled comb‑spacing sweeps. However, symmetric comb‑spacing sweeps fix the center wavelength, causing phase localization and fringe‑free interference peaks whose amplitudes vary with phase and vanish at π/2, result in unmeasurable blind regions as reported previously. To address this limitation, we incorporated sinusoidal phase modulation (SPM) technique, thereby eliminating the blind regions by rendering the π/2‑phase null interference signal detectable. Furthermore, aligning amplitude‑peak and stationary‑phase distributions obtained from comb‑spacing sweeps and SPM enabled submicron‑accurate 3D full‑field topography. This phase‑stabilized tomography approach achieved displacement accuracy beyond the limit imposed by the interference‑peak width. The system acquires a 640 × 518 × 865‑voxel volume within one second, enabling high‑speed full‑field tomography. The technique’s effectiveness is demonstrated through measurements of a step‑height standard, a non‑specular coin surface, and a glass plate, confirming its capability for high‑speed, high‑precision full‑field profiling and tomography.