Algorithm-free optical phase recovery via Kerr-induced in-fiber interferometry

Optical phase information is fundamental to sensing, imaging, and telecommunication. Conventional phase recovery techniques rely on interferometric setups with reference arms or computationally demanding algorithms. This work presents a reference- and algorithm-free method for local and distributed phase recovery using weak nonlinear effects in optical fibers. By operating in low-power regimes, self-phase modulation maps input phase directly to measurable spectral intensity. The approach achieves linear correlation (Pearson correlation ≈ 0.98) between input phase and output spectrum using standard fiber components in a fully fiber-integrated setup. Simulations of phase-encoded images and experimental validation using a waveshaper and dispersive Fourier transform measurements at 80 MHz demonstrate real-time, distributed phase retrieval. These results highlight nonlinear fibers as a compact platform for fast, reference-free phase sensing.