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Journal of the Optical Society of America A

Characterizing the fractional coherence vortices through the area of the intensity cross-correlation function

Patnala Vanitha, Youngbin Na, Do‐Kyeong Ko

Published Jun 7, 2024• 9 citations
Publisher

Abstract

We have generated the fractional coherence vortices using the speckle patterns obtained from the scattering of the fractional vortex beams. In this study, we found the topological charge of the fractional vortex beam with a resolution of 0.01 using the area of the coherence function of scattered fractional optical vortex beams. We have also provided accuracy for the measurement of topological charges of fractional vortex beams using the studies of the area of the coherence function. Our experimental results are well matched with the theoretical results. These fractional coherence functions can be used to generate a security key for data authentication and data encryption. In addition, fractional vortex beams have multiple OAM modes and can be used to address the explosive growth in free-space optical communication.

DOI
10.1364/josaa.527925

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Vortex beams with different topological charge usually have different profiles and radii of peak intensity. This introduces a degree of complexity the fair study of the nature of optical OAM (orbital angular momentum). To avoid this, we introduced a new approach by creating a perfect vortex beam using an annular illuminating beam with a fixed intensity profile on an SLM that imposes a chosen topological charge. The radial intensity profile of such an experimentally created perfect vortex beam is independent to any given integer value of its topological charge. The well-defined OAM density in such a perfect vortex beam is probed by trapping microscope particles. The rotation rate of a trapped necklace of particles is measured for both integer and non-integer topological charge. Experimental results agree with the theoretical prediction. With the flexibility of our approach, local OAM density can be corrected in situ to overcome the problem of trapping the particle in the intensity hotspots. The correction of local OAM density in the perfect vortex beam therefore enables a single trapped particle to move along the vortex ring at a constant angular velocity that is independent of the azimuthal position. Due to its particular nature, the perfect vortex beam may be applied to other studies in optical trapping of particles, atoms or quantum gases.
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A medical care system’s security, high-capacity information transfer, and communication are all dependent on OAM-based quantum key distribution, namely on the measurement of OAM’s topological charges (TCs). The intensity patterns of interference between the vortex beam and its conjugate beam are analyzed to detect and evaluate positive and negative TCs of Laguerre-Gaussian (LG) vortex beams in a novel manner. An upgraded Mach–Zehnder (M-Z) interferometer is used to establish the order of positive, negative, integer, and half-integer TCs. Deciphering the order of integer TCs and half-integer TCs may be accomplished by measuring the interference bright petals as well as half of the total numbers of bright petals. The integer and half-integer TCs (VPP) may be modulated by the use of light path rotational with a vortex stage plate. Using the interferometer as mentioned earlier, the positive and negative of integer and half-integer TCs are acquired. Quantitatively, the order and sign of integer and half-integer TCs are measured in this manner. And this method is straightforward and less susceptible to the influence of parasitic interference. This can provide comprehensive security protection for the medical monitoring system, better reduce medical risks and protect patient privacy.
We present a compact intensity interferometer designed to synthesize the second-order complex correlation function through intensity correlation measurements. By leveraging the diffraction-multiplexed vortex generation capability of a Dammann vortex grating alongside a holographic intensity correlation technique, our system generates tunable one- and two-dimensional correlation vortex array patterns. This advancement enables applications in optical communication and orbital angular momentum encryption, offering robust stability and propagation adaptability in diverse environments.
Orbital angular momentum (OAM) of photons has applications both in classical and quantum information due to its features of optical vortex and infinite dimensions. This paper studies the interference effects of optical vortex beams carrying mixed, conjugate, and single-mode OAM states based on the Sagnac interferometer with light sources of a laser and single photon. We compare our results with numerical simulations and show that the light intensity distribution and phase characteristics can directly characterize the absolute value of the topological charge (TC) carried by vortex beams. Furthermore, our scheme can also classify the photon with positive and negative signs of TC in the mixed mode OAM state by changing the relative phase. The results not only extend the manipulation methods for high-dimensional quantum states, but also lay a solid foundation for the application of vortex beams in a single-photon field.