Single code pseudo-random quadrature phase shifting homodyne interferometry

Digitally enhanced homodyne interferometry traditionally uses two pseudo-random noise codes to form a quadrature phase shifting modulation. It enables the recovery of interference phase information alongside time-of-flight range gating, with upfront modulation. Here, we propose a "single-code" modulation scheme, generated from a single m-sequence pseudo-random noise code while retaining a 4-level phase step required for double modulated homodyne detection. We numerically verify the modulation preserves an m-sequence autocorrelation profile, and experimentally characterize the phase recovery performance of the scheme. We characterise the coupling of relative intensity noise and demonstrate an optical sensitivity of 3 µrad/Hz.