Generation of NIR and Visible Structured Light Beams with a Mechanical Long-Period Fiber Grating

TL;DR

This paper demonstrates a tunable method to generate various structured light beams at 1060 nm using a mechanically controlled long-period fiber grating in a few-mode fiber, enabling precise mode manipulation for advanced optical applications.

Contribution

It introduces a novel mechanically tunable fiber grating technique for generating and controlling structured NIR and visible light beams with high precision.

Findings

Able to generate vortex, vector, and flat-top beams at 1060 nm

Controlled mode excitation by varying applied force and polarization

Achieved propagation-invariant flat-top beams over 5 meters

Abstract

This work presents the tunable generation of vortex, vector, and flat-top 1060-nm NIR beams in a few-mode fiber with a mechanical long-period fiber grating. By the variation of applied force on the fiber grating, the core mode to higher-order mode excitation can be adjusted. The manipulation of the beam transformation is achieved through the polarization control of the fiber eigenmodes and mode coupling efficiency. By precisely tuning the intensity ratio between fundamental and doughnut modes, we arrive at the generation of propagation-invariant vector flat-top beams for more than 5 m. Transverse optical field of 532-nm green light from frequency-doubled Nd-doped yttrium vanadate laser is manipulated and coupled into various intensity distributions in a few-mode fiber by using a mechanically induced long-period fiber grating. We show that the doughnut beam, the Mexican-hat beam, and the crater-lake beam can be generated from the input Gaussian beam via the coupling of the fundamental core mode to a series of co-propagating higher-order modes with properly applied forces and polarizations.