Minimizing non-orthogonality in homodyne interferometers with a continuously tunable phase-shifted triple-channel optical configuration

Traditional multi-channel configuration in homodyne interferometers introduces phase shifts with wave plates to generate a pair of quadrature sinusoidal signals. However, orthogonality deviations inevitably exist due to imperfections in PBS/NPBS. This Letter proposes a tunable phase-shifted triple-channel optical configuration that enables continuous phase-shift adjustment over [-π, π] despite component imperfections. By differencing π/2 + Δφ, 0 + Δφ, and π + Δφ phase signals with the electric circuit, a pair of sinusoidal signals with good orthogonality and suppressed DC offset was obtained. Experiments showed orthogonality better than 0.03°, nonlinear error in the original signal <0.6 nm, and the nonlinear error can be further reduced to <0.03 nm after correction of residual DC offset.