Abstract The coherent control of orbital angular momentum four-wave mixing (OAM-FWM) signal in a cascaded three-level atomic system by multiple parameters of incident lights is studied. Firstly, based on the Laguerre–Gaussian beam, the expressions for the intensity and phase of the FWM signal loaded with OAM were derived by solving the density matrix equation in the steady state. Then, through coordinate transformation, the spatial distribution construction of the OAM-FWM signal was completed. And the spatial structure of intensity and phase distribution are investigated respectively. It is shown that the Rabi frequency and detuning can effectively control the output OAM-FWM signal. Finally, we further study the phase distribution of multiple topological charge (TC) numbers in the FWM process, considering the conservation of OAM. As a result, the signal can also be regulated by multiple TC numbers. The constructed OAM-FWM signal which has enhanced the information storage capacity, could be widely used in optical communication and quantum information research.
Abstract The coherent control of orbital angular momentum four-wave mixing (OAM-FWM) signal in a cascaded three-level atomic system by multiple parameters of incident lights is studied. Firstly, based on the Laguerre–Gaussian beam, the expressions for the intensity and phase of the FWM signal loaded with OAM were derived by solving the density matrix equation in the steady state. Then, through coordinate transformation, the spatial distribution construction of the OAM-FWM signal was completed. And the spatial structure of intensity and phase distribution are investigated respectively. It is shown that the Rabi frequency and detuning can effectively control the output OAM-FWM signal. Finally, we further study the phase distribution of multiple topological charge (TC) numbers in the FWM process, considering the conservation of OAM. As a result, the signal can also be regulated by multiple TC numbers. The constructed OAM-FWM signal which has enhanced the information storage capacity, could be widely used in optical communication and quantum information research.
Abstract The spatial structure and propagation of vortex Four-Wave mixing (FWM) generated in a cascade three-level atomic system when Laguerre-Gaussian (LG) beams are used as the incident pump fields are studied. Firstly, by solving the third-order density matrix elements in the steady state, the intensity expression of the vortex FWM signal is obtained. Next, their spatial image and phase during the propagation process are researched. It is shown that with the increase of propagation distance, its image of the intensity tends to a Gaussian beam, and the center of the spot gradually deviates from the original optical singularity. Furthermore, after superposing multiple topological charge (TC) numbers, the intensity and phase images present entirely different light spots at various positions. The TC number can rapidly increase the capacity of the signal for carrying information. This type of signal can be utilized in quantum communication and information, offering a scalable light source for high-dimensional quantum storage.
Abstract We study various coherent optical properties, e.g., two-photon electromagnetically induced transparency (EIT) and three-photon electromagnetically induced transparency and absorption (TPEIT/TPEIA), in a four-level ladder (Ξ)-type system of 87Rb atoms, where the probe and control fields are Gaussian-shaped laser beams and the pump field is structured laser beam. Additionally, the generated four-wave mixing (FWM) signal has been studied. Interestingly, it is found that the generated FWM signal is spatially structured along with the azimuthal phase, which carries the orbital angular momentum (OAM) of light. It is also observed that the coherent optical responses (EIT, TPEIT/TPEIA, and FWM signals) can be manipulated by utilizing the OAM number of the pump beam as a control knob.
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.
We explore the conservation of orbital angular momentum (OAM) in the four-wave mixing (FWM) process in hot rubidium vapor. Since most modern communication systems send data in pulses corresponding to bits, we can use OAM to encode more information in each pulse by assigning structure to each signal. Furthermore, because FWM can be used to generate entangled photon pairs, we can use this process to bring enhanced signal security. We experimentally studied FWM with a wide range of Laguerre-Gaussian modes and their superpositions and observed OAM transfer from the probe field to a generated Stokes field. By studying the output Stokes intensity and phase distributions, we confirm l mode (OAM) conservation for pure l and p modes, as well as for the superpositions of l and -l for the mode numbers up to l = 4, p = 4. We also found that p index is generally not conserved and its conservation is highly dependent on the relative sizes of the probe and pump beams in the Rb cell. We also identify parameters to improve FWM gain with OAM transfer and propose an analytical method for determining OAM p number.
Magnet-free optical nonreciprocity has significant applications in quantum communication, quantum networks, and optical information processing. In this research, considering a degenerate two-level thermal atomic system with the Doppler effect of thermal atoms, the nonreciprocal amplification (NRA) of dual-path degenerate four-wave mixing (FWM) signals is achieved under the action of a co-propagating pumping field. On this basis, spatially multiplexed multiple FWM processes are formed by introducing another counter-propagating pumping field, thereby achieving the reciprocal amplification (RA) of the dual-channel FWM signals. Furthermore, by using multiple sets of spiral phase plates to load spiral phases on the signal light and the pumping light respectively, higher-order Laguerre-Gaussian vortex beams carrying different optical orbital angular momentum (OAM) are generated and participate in the FWM process, achieving the transfer of the OAM of the pumping light to the amplified FWM fields. Simultaneously, using the Mach-Zehnder interferometer, the conservation characteristics of the OAM of each FWM signal in the NRA-RA conversion are further analyzed. Furthermore, experimental results demonstrate that in the multiple FWM process induced by a pair of counter-propagating pump fields, the OAM of the amplified FWM signal in each channel varies with that of the pump field. However, the overall process maintains the OAM conservation. This study provides a feasible solution for expanding the channel capacity using OAM based on NRA-RA system, showing that the OAM has potential application prospects in achieving high-capacity optical communication and multi-channel signal processing.
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.