Mode Conversion and Transfer of Orbital Angular Momentum Between Hermite-Gaussian and Laguerre-Gaussian Beams

Donghui Shen,Tong He,Daomu Zhao,Xianbin Yu

doi:10.1109/jphot.2022.3140359

Abstract

The cross phase (CP) opens up a new horizon for the generation and measurement of vortex beams, and the conversion between Hermite-Gaussian (HG) and Laguerre-Gaussian (LG) modes can be done with a CP. However, the conversion plane is in the far plane, and the width cannot be adjusted. In this article, we present a more convenient and practical mode converter between HG and LG modes based on CP combined with a lens. The feasibility of the converter for the conversion between two modes is theoretically analyzed. The conversion can be accomplished in the determined plane and the width of converted beam can be controlled by adjusting the parameter of converter. Proof-of-concept experiment is carried out to verify theoretical analysis and the experimental results are agree well with theoretical simulations. The transfer of orbital angular momentum (OAM) between two modes after passing through the converter is also analyzed. From the perspective of OAM conservation, the required parameter conditions for the converter are discussed. In principle, such a converter as proposed here might even be applied to microwave, millimeter wave, and terahertz OAM fields.

Highlights

H ERMITE Gaussian (HG) beams and Laguerre Gaussian (LG) beams are the most well-known solutions of the paraxial equation, and these beams have been the interesting subjects since 1960’s [1]
The generated beam passes through a cross phase (CP) lens phase screen, which is loaded on the second spatial light modulator (SLM)
It is straightforward to show for a HG beam or LG beam that the change in orbital angular momentum (OAM) on passing through a combined with a lens (CP lens) is given by δLHz G

Summary

INTRODUCTION

H ERMITE Gaussian (HG) beams and Laguerre Gaussian (LG) beams are the most well-known solutions of the paraxial equation, and these beams have been the interesting subjects since 1960’s [1]. The OAM has been generally recognized as a fundamental property of electromagnetic waves, attracting many research interests in optical fields [3]–[6]. The measurement methods of OAM are mainly based on the interference and diffraction properties of vortex beams. One can use this robust mode converter to generate OAM beams or measure the OAM of optical field [28]. Such a converter can be integrated into an optical device with diffractive optical elements (DOE) technique, and the device has simple adjustment and reliable performance [29]. Theoretical analysis and experimental results are both presented below, and the experimental results agree well with theoretical simulations

THEORETICAL ANALYSIS

EXPERIMENTAL SETUP AND RESULT

OAM TRANSFER

CONCLUSION