Orbital angular momentum complex spectrum analyzer for vortex light based on the rotational Doppler effect.

The ability to measure the orbital angular momentum (OAM) distribution of vortex light is essential for OAM applications. Although there have been many studies on the measurement of OAM modes, it is difficult to quantitatively and instantaneously measure the power distribution among different OAM modes, let alone measure the phase distribution among them. In this work, we propose an OAM complex spectrum analyzer that enables simultaneous measurements of the power and phase distributions of OAM modes by employing the rotational Doppler effect.