Orbital angular momentum comb with customizable intensity distribution

The orbital angular momentum (OAM) of light, arising from helical phase structure, has attracted great interest due to its wide applicability. The orthogonality among different OAM modes and their potentially unbounded dimensionality make OAM a powerful resource for constructing high-dimensional Hilbert spaces. Consequently, flexible and precise control over the OAM spectra is of great importance in both classical and quantum optics. Several techniques have been developed for the on-demand generation of arbitrary OAM spectra, including OAM combs. However, most of the input beams are confined to a Gaussian-like fundamental mode with a uniform azimuthal intensity distribution. In this work, we introduce a novel approach that efficiently shapes the OAM spectrum using pure phase modulation, applicable not only to the input Gaussian beam but also to input beams with azimuthally inhomogeneous intensity profiles. Our approach is experimentally demonstrated by converting an input Gaussian beam and various azimuthally structured beams into desired OAM combs and arbitrary OAM spectra. Our results not only expand the toolkit for the highly efficient generation of OAM combs but also provide a straightforward and effective means to control the OAM spectrum for non-uniform input optical fields.