Abstract The manipulation of the orbital angular momentum (OAM) contributes to understand the OAM multiplexing, is significant in free-space optical communication and information processing. We theoretically simulate and experimentally demonstrate the regularity of the OAM transfer, including the angular and radial modes, of Laguerre–Gaussian beam via four-wave mixing process in 85Rb vapor. The 420 nm coherent blue light output field inherits the phase characteristic of 780 nm and 776 nm beams with different OAM modes. The output field OAM modes show the transfer as a typical arithmetic operation of the input field OAM modes with equal-handed angular indice l, while, the conversion between angular and radial modes occurs with the opposite angular indice l. Such rules of the OAM transfer and manipulation have implications on the research of high-capacity information transfer and quantum communication.
Vortex light, a unique optical field that carries orbital angular momentum (OAM), has attracted considerable attention in recent years. In this paper, we present a detailed theoretical analysis of OAM transfer from the input field to the generated signal field in a four-level double-Lambda system via the four-wave mixing (FWM) process, showing that their OAMs follow a specific algebraic relationship. We identify the optimal conditions for efficient vortex light transmission, analyze the influence of detuning on transmission efficiency and phase distortion, and specifically examine the scenario where the control field carries OAM the latter being essential for a complete characterization of OAM conservation in the FWM process, while all three aspects have been largely overlooked in the existing literature. Furthermore, we investigated the tunability of the group velocity between the probe and signal fields by modulating the Rabi frequencies of the two control fields and the relative phase between the probe and signal fields during the FWM process. We demonstrate that the conversion between matched vortex slow and fast light can be realized an effect that has not been widely explored in dual-Lambda-type systems. These results may hold promise for applications in quantum information storage and processing, quantum computing, and ultrasensitive detection.
Abstract We propose a rotation-controlled nonlinear orbital-angular-momentum (OAM) filter based on photonic-band-gap-assisted four-wave mixing (PBG-FWM) in rubidium vapor. The model follows the field convention of PBG-FWM experiments: an OAM probe field
E1 is Bragg-reflected through the nonlinear polarization produced with two counterpropagating Gaussian coupling fields
E3 and
E3′, while the generated field is denoted by
EF. The coupling pair forms a standing-wave Rabi frequency
∣G3s∣2=∣G3∣2+∣G3′∣2+2G3G3′cos(2k3z), which creates the longitudinal PBG modulation and enters the resonant denominator of the third-order susceptibility. Rotation adds an OAM-dependent rotational Doppler shift to the probe and generated FWM modes. In a slow-light PBG-FWM medium this shift is converted into a longitudinal phase-matching perturbation, giving
ηm(Ω)=η0sinc2[Δkrot(m)L/2] in the phase-matching-dominated limit. Rotation can also perturb
χ(3) through Doppler-shifted detunings, producing envelope and asymmetry corrections. The theory predicts OAM-dependent FWM quenching, the readable petal rotation, and a rotationally tunable OAM cutoff. The results provide a design route for rotation-sensitive structured-light processing in atomic nonlinear media.