Intersecting of circular apertures to measure integer and fractional topological charge of vortex beams

Precision measurement of the topological charge of a fractional vortex beam based on angular-grating-diffraction OAM spectrum

Vortex light beams carrying fractional vortices have shown promising applications in many fields such as optical communications, optical encryption, and quantum information processing. Accurate detection of the topological charge of a fractional vortex phase is essential for these applications. In this paper, a simple yet effective method for measuring the fractional topological charge is proposed, which is based on the detection of the orbital angular momentum (OAM) spectrum of a fractional vortex beam diffracted by an angular grating. When the fractional vortex beam passes through an angular grating, the OAM spectrum broadens, increasing the number of detectable OAM components. By applying nonlinear least squares fitting to the broadened spectrum, the topological charge can be detected with high precision. Experimental results demonstrate the detection range for fractional topological charges is from -6 to 6, with a resolution of 0.01 and an error of less than 0.005. Our protocol offers significant potential for high-capacity information transfer.

Topological charges measurement of circular Bessel Gaussian beam with multiple vortex singularities via cross phase

In this paper, we firstly propose a method to measure the topological charges (TCs) of a circular Bessel Gaussian beam with multiple vortex singularities (CBGBMVS) by utilizing cross phase. Based on theory and experiment, the cross phase is utilized to realize the TCs measurement of the CBGBMVS in free space with different situations, such as different singularity number, TCs and singularity location. Especially, the TCs measurement method is also investigated and verified in atmosphere turbulence. Our work provides an effective and convenient way to realize the TCs measurement of multiple singularities embedded in abruptly autofocusing host beams which has plenty of potential application in optical communication.

Fractional topological charge measurement through optical correlation

The emerging field of optical vortex beams having fractional topological charges (TCs) is of high interest due to its usefulness in various applications. The efficiency of the result depends on the precise measurement of the orbital angular momentum information tied to the fractional TC. This Letter demonstrates, to our knowledge, a novel and simple technique to measure the fractional TC of optical vortex beams through a hybrid digital-optical correlator with the help of auto-correlation between fork-shaped interference patterns corresponding to integer and fractional TCs. Unlike machine learning-based approaches, the proposed method does not require a complex architecture, which lowers computational cost and enables real-time implementation.