Fast and efficient OAM mode detection for optical communications via rotating Poincaré beams

We present a fast and efficient method for detecting the orbital angular momentum (OAM) difference between optical modes using Poincar´e beams formed by the superposition of two Laguerre-Gaussian modes of topological charges ℓ1 and ℓ2, with orthogonal circular polarizations. When projected through a linear polarizer at 45°, the beam forms a petal-like intensity pattern, where the number of petals corresponds to Δℓ = ℓ2−ℓ1. By introducing a varying phase shift, the pattern rotates azimuthally. Two fixed photodetectors measure sinusoidal intensity signals as the pattern rotates, with a phase difference that varies linearly with Δℓ. This allows rapid, imagefree identification of OAM differences using only two detectors. The method offers a low-complexity, real-time alternative to conventional OAM detection techniques, making it ideal for applications in optical communication and mode-division multiplexing where speed and scalability are critical.