Mode-dependent phase in waveguides supporting orbital angular momentum

We report experimental measurements of mode-dependent phase accumulation in waveguides supporting orbital angular momentum (OAM) modes. By analyzing the output phase profiles for different OAM states, we extracted relative phase shifts induced by variations in waveguide radius and refractive index contrast. We find that the phase shift depends on the modulus of the topological charge and is governed by the propagation constant, which is modulated by transverse confinement effects. These phase variations manifest as a rotation of the optical wavefront and are in excellent agreement with theoretical predictions. Our findings establish a passive and deterministic mechanism for mode-selective phase control in integrated photonic platforms, with direct implications for scalable high-dimensional quantum information processing and structured light-based optical communications.