Simulation of near-diffraction- and near-dispersion-free OAM pulses with controllable group velocity by combining multiple frequencies, each carrying a Bessel mode
Kai Pang, Kaiheng Zou, Hao Song, Zhe Zhao, Amir Minoofar, Runzhou Zhang, Haoqian Song, Huibin Zhou, Xinzhou Su, Cong Liu, Nanzhe Hu, Moshe Tur, Alan E. Willner
Abstract
Optical pulses carrying orbital angular momentum (OAM) have recently gained interest. In general, it might be beneficial to simultaneously achieve: (i) minimum diffraction, (ii) minimum dispersion, and (iii) controllable group velocity. Here, we explore via simulation the generation of near-diffraction-free and near-dispersion-free OAM pulses with arbitrary group velocities by coherently combining multiple frequencies. Each frequency carries a specific Bessel mode with the same topological charge ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>ℓ</mml:mi> </mml:math> ) but different <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi>k</mml:mi> <mml:mi>r</mml:mi> </mml:msub> </mml:mrow> </mml:math> (spatial frequency) values based on space–time correlations. Moreover, we also find that (i) both positive and negative group velocities could be achieved and continuously controlled from the subluminal to superluminal values and (ii) when the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>ℓ</mml:mi> </mml:math> is varied from 0 to 10, the simulated value of the group velocity remains the same. However, as the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>ℓ</mml:mi> </mml:math> value increases, the pulse duration becomes longer for a given number of frequency lines.