Fiber Bragg Grating-Based Tunable Wavelength Orbital Angular Momentum Beam Generation with Varying Polarization

Abstract

This paper introduces and theoretically analyze the generation of orbital angular momentum (OAM) modes with different polarization in a few-mode optical fiber using short-period gratings (Bragg gratings) at telecommunication wavelengths. The modal characteristics of the supported modes have been studied using a full-vector true-mode analysis. Additionally, a appropriately designed raised-cosine apodized grating is employed to couple the HE₁₁ core mode to the counter-propagating cladding mode. In contrast to the long-period grating based OAM mode generation, the present scheme is free from periodic back-coupling of optical power into the fundamental core mode which drastically enhances the OAM mode purity. The ±1-order OAM beam has been generated by combining the first higher order core modes with a π/2 phase shift between them. This paper also shows that by combining different higher order modes, it is possible to obtain a linearly polarised OAM mode or a circularly polarised OAM mode. Finally, I also report that in fibers with larger core radius, the higher order OAM mode of topological charge ±2 or higher can also be generated using similar approach of using short-period gratings. The topological charge of the OAM mode is verified by observing both the coaxial and off axial interference fringes.

Received: 13 March 2024 | Revised: 3 June 2024 | Accepted: 25 November 2024

Conflicts of Interest

The author declares that he has no conflicts of interest to this work.

Data Availability Statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Author Contribution Statement

Avijit Koley: Conceptualization, Methodology, Software, Validation, Formal analysis, Data curation, Writing - original draft, Writing - review & editing.