Search

Optical angular momentum (OAM) in light beams is manifested as the two-dimensional spatial distribution of its complex amplitude, necessitating a 2D detector for its measurement. Here we present a novel speckle-based machine learning approach for OAM recognition, which enables recognition using a 1-D array detector or even a 0-D single-pixel detector., Comment: 16TH International Conference on Fiber Optics and Photonics, 12-15 December, 2024, IIT Kharagpur,India

Orbital angular momentum (OAM)-carrying beams have gained significant attention in recent years due to their unique properties and potential to improve spectral efficiency and data transmission rates in optical communication systems. However, fully exploiting the capabilities of the entire OAM mode spectrum remains challenging. The emergence of AI-driven OAM mode identification has revolutionized the demultiplexing process within optical communication channels. OAM beams with different orders are orthogonal, allowing each beam to serve as a distinct signal carrier. Combining multiple OAM beams can effectively enhance channel capacity. In this paper, we adopt speckle-learned demultiplexing to demultiplex OAM beams via its speckle pattern that is more resilient to alignment and noise. However, the use of only non-intensity degenerate beams limits the utilization of multiplexing resources. This approach aims to fully leverage the full spectrum of OAM beams by introducing astigmatism in far-field speckle patterns using a tilted spherical convex lens. We then conduct a comprehensive analysis of two innovative information encoding techniques: OAM shift keying and OAM multiplexing. We successfully demonstrate an optical communication link encoded using both OAM shift keying and OAM multiplexing, followed by accurate decoding via speckle-learned demultiplexing.

In this paper, the advancements in structured light beams recognition using speckle-based convolutional neural networks (CNNs) have been presented. Speckle fields, generated by the interference of multiple wavefronts diffracted and scattered through a diffuser, project a random distribution. The generated random distribution of phase and intensity correlates to the structured light beam of the corresponding speckle field. This unique distribution of phase and intensity offers an additional dimension for recognizing the encoded information in structured light. The CNNs are well-suited for harnessing this unique ability to recognize the speckle field by learning hidden patterns within data. One notable advantage of speckle-based recognition is their ability to identify structured light beams from a small portion of the speckle field, even in high-noise environments. The diffractive nature of the speckle field enables off-axis recognition, showcasing its capability in information broadcasting employing structured light beams. This is a significant departure from direct-mode detection-based models to alignment-free speckle-based detection models, which are no longer constrained by the directionality of laser beams.