Figure 7: Schematics of the four-quadrature phase-stepper (lateral view); : signal light, : reference light, HWP: half-wave plate, L2-3 Lenses, NPBS: nonpolarizing beam splitter, M1–3: mirrors, QWP: quarter wave plate, CGP: compensation glass plate, WP: wollaston prism, D (5 mm) corresponds to the half-size of NPBS. Inset shows the separation of incident beam into two orthogonally polarized images by the Wollaston.