Efficient generation of a high-uniformity orbital angular momentum comb via cross-phase modulation

Orbital angular momentum (OAM) of photons provides an additional degree of freedom by accessing the spatial structure of light and has benefited applications from classical to quantum photonics. Here we develop a simple scheme to produce an OAM comb-a structured mode comprising multiple, equally spaced OAM components with near-uniform power-using a single cross-phase (CP) modulation. We show that embedding a CP term into a pure OAM mode converts it into a beam with a broadened, tunable OAM spectrum, whose modal distribution is governed by the CP coefficient and the beam waist. Increasing either parameter not only broadens the spectrum but also drives the modal weights toward equalization, leading to a highly uniform OAM comb. Experiments agree well with theory and yield an OAM comb with 93.5% spectral uniformity. This approach is convenient to implement, avoids amplitude-modulation loss, and opens new opportunities for OAM spectrum manipulation in high-security holographic encryption, high-capacity data transfer, and other advanced photonic systems.