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Frontiers in Physics

Capturing the amplitude and phase profile of the vortex beam based on coherent detection

Shengmei Zhao, Quanqing Qiao, Le Wang

Published Aug 17, 2022• 4 citations
Publisher

Abstract

In this study, we propose a scheme to capture the amplitude and phase profile of the orbital angular momentum (OAM) beam based on coherent detection. In the scheme, the OAM beam to be measured is interfered with a local plain wave which is prepared at the receiver, and two charge-coupled devices (CCDs) are used to record the constructive and destructive interference patterns. By setting the phase of the plain wave to π/2 and π, one can extract the amplitude and phase profile of the OAM beam from the two interference patterns. We verify the feasibility of the scheme by simulation and experiments. The results show that both amplitude and phase profiles of single OAM and OAM superposition modes can be captured by using the proposed scheme, and the proposed scheme shows strong robustness even under the presence of atmospheric turbulence.

DOI
10.3389/fphy.2022.879826

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In this study, we propose a scheme to capture the amplitude and phase profile of the orbital angular momentum (OAM) beam based on coherent detection. In the scheme, the OAM beam to be measured is interfered with a local plain wave which is prepared at the receiver, and two charge-coupled devices (CCDs) are used to record the constructive and destructive interference patterns. By setting the phase of the plain wave to π/2 and π, one can extract the amplitude and phase profile of the OAM beam from the two interference patterns. We verify the feasibility of the scheme by simulation and experiments. The results show that both amplitude and phase profiles of single OAM and OAM superposition modes can be captured by using the proposed scheme, and the proposed scheme shows strong robustness even under the presence of atmospheric turbulence.
The orbital angular momentum (OAM) of a vortex beam has already found significant potential applications in both quantum and classical communication systems. In this study, a realization of a double-slit experiment using a Sagnac interferometer is conducted for the detection and discrimination of vortex beams. Based on the advantages of convenient and adjustable double-slit parameters of our device, we detected multiple vortex beams carrying different OAM modes and superpositions of OAM modes under laser and single-photon illumination. We also analyzed the influence of the slit parameters on the interference pattern of the vortex beams. The results show that by comparing the differences in these interference patterns, we can achieve the measurement of topological charge and complete distinction of OAM states carried by the vortex beams. Our study contributes to coding research on laser and quantum communication.
In the paper, we present a method for the measurement of the orbital angular momentum (OAM) superposition state by making use of the characteristics of the beam's helical phase structure and Gouy phase. With the rotation angle and the petal-like number of the OAM superposition state, one can efficiently extract the component OAM mode of the OAM super-position state by the method. We derive the simple relationship between the OAM superposition state's rotation angle and the propagation distance, which is verified by numerical simulations and experiments. The results show that the proposed method can detect the sign and the topological charge of the component OAM modes. Additionally, the proposed method has a higher fault tolerance and has significance for optical communication based on OAM superposition state.
Nonlinear interaction between orbital angular momentum (OAM) modes provides an enticing promise for realizing high-dimensional quantum states and multimodal communications. Here, we demonstrate the inter-modal interference of OAM modes based on the nonlinear frequency conversion of perfect vortex beams, permitting the arbitrary spatial intensity and phase information to be transformed and manipulated from 778 nm input beam to 420 nm output beam. The conversion of single OAM state obeys the typical arithmetic operation. In contrast, the conversion of superposition state is predicted and revealed as the inter-modal interference of full spatial complex amplitude. For the allowed OAM modes, the probability amplitude is quantitatively analyzed by the intensity overlap of input OAM modes, which determines the degree of degradation in the intensity and phase. As a result, the output beam exhibits the nonuniform petal-shaped intensity and phase distributions under the conditions of phase matching and OAM conservation. Furthermore, the inherent transverse structure invariance of perfect vortex beams enables them to accommodate and support larger OAM values and more superposition states.
This study presents an innovative scheme for detecting the orbital angular momentum (OAM) of vortex beams within an atomic ensemble. Leveraging a homogeneously broadened four-level atomic system driven by two orthogonal polarization probe beams, we demonstrate the selective generation of structured beams without the need for magnetic fields between the two ground states. Through detailed theoretical analysis and numerical simulations, we elucidate the phase-dependent behavior of atomic coherences induced by an OAM-carrying Laguerre–Gaussian optical probe beam. These findings enable the creation of petal-like structures within the probe beam, with the number of petals directly correlated to the OAM value. Our investigation underscores the potential of this OAM detection scheme as a highly sensitive and precise sensor, applicable across diverse domains such as telecommunication, microscopy, and optical metrology.
We propose a scheme to map atoms via the coherence superpositions of orbital angular momentum (OAM) light. The atoms are prepared in the four-level tripod configuration in the presence of a vortex light, which coherently superposes two Laguerre-Gaussian (LG) beam modes with equal but opposite OAM. Because of the spatially dependent atom-field interaction, the information about the position of the atom can be obtained via the absorption measurement of the weak probe field. It is found that the absorption behavior is significantly impacted by the detuning, control field, azimuthal number, and radial number. Most importantly, atomic mapping accuracy can be controlled by properly adjusting the detunings and control field. The coherent interaction of OAM light with atoms constitutes a platform for active mapping of atoms at specific positions in azimuthal space.
Based on our constructed robust π/2 mode converter, we report a concise yet high-efficient experiment to realize the detection of high-order orbital angular momentum (OAM). The π/2 mode converter that consists of a pair of cylindrical lens is actually not new. However, our experiment show clearly its excellent robustness, as we have detected the high-order OAM numbers up to ℓ = 150 carried by standard Laguerre-Gaussian (LG) modes. The observed patterns of two-dimensional optical lattices indicate that the radial index p of LG beams can be straightforwardly inferred as well. Our demonstration has potential in both classical and quantum information applications where high OAM modes are needed.