Inter-modal Raman amplification of OAM fiber modes

Jacob Gade Koefoed,Karsten Rottwitt,Poul Kristensen,Kasper Ingerslev

doi:10.1063/1.5051794

Jacob Gade Koefoed, Karsten Rottwitt + Show 2 more

Open Access

https://doi.org/10.1063/1.5051794

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Abstract

Raman scattering among conventional linearly polarized (LP) modes in single mode optical fibers is generally accepted as a promising way to achieve distributed amplification due to the fact that Raman amplification may provide gain at any wavelength, determined by the used pump wavelength, and excellent noise performance. Here, we show that Raman scattering among orbital angular momentum (OAM) modes in optical fibers have similar properties. We show theoretically that the Raman gain among OAM modes is independent on the topological charge of the OAM modes and that the gain efficiency when the pump and signal are parallel (orthogonally) polarized is similar to the Raman scattering among LP modes in parallel (orthogonal) states of polarization. In addition, we experimentally characterize Raman gain among OAM modes in a fiber supporting multiple OAM modes for both the pump and signal. Finally, we discuss the impact of polarization mode dispersion.

Highlights

Modes in optical fibers that carry orbital angular momentum (OAM) have recently received strong interest
We have theoretically described the Raman interaction among vortex modes, with emphasis on orbital angular momentum (OAM) modes
We have shown that the Raman gain provided by an OAM mode to an OAM mode depends on the state of polarization but not on the topological charge

Summary

INTRODUCTION

Modes in optical fibers that carry orbital angular momentum (OAM) have recently received strong interest. OAM modes have been suggested as a key to address the everlasting need for more and more capacity in classical communication systems, a need that is currently pushing optical communication systems towards mode-division multiplexing In this regard, applications of OAM modes hold great promise, especially when considering short range data transmission, for example, in datacenters. Optical fibers that support stable propagation of OAM modes are different from SMFs. Suggested designs consist of an air core surrounded by a ring of relatively high refractive index compared to the cladding.. We compare the Raman gain among different combinations of pump and signal OAM states

THEORY

Propagation equations

The Raman effective area

The effective Raman susceptibility

Polarization dependence

Impact of PMD

Cyclic coordinates

EXPERIMENTAL CHARACTERIZATION

CONCLUSION