Prof. Nianqiang Li

School of Optoelectronic Science and Engineering, Soochow University, China

Speech Title: Optically pumped spin-VCSELs

Abstract

Spin-polarized vertical-cavity surface-emitting lasers (spin-VCSELs) are known to support high-frequency continuous birefringence-induced oscillations whose frequency is not determined by the relaxation oscillation (RO) mechanism usually recognized in conventional laser diodes. However, this depends on the pumping condition as well as some key parameters, since electric pumping or hybrid pumping only results in damped high-frequency birefringence-induced oscillations. Here we focus on the optically pumped spin-VCSELs which have not been fully understood compared to those under hybrid pumping. We consider both periodic and continuous-wave (CW) regimes for exploiting high-frequency operation. The two regimes are restricted by the Hopf bifurcation boundaries. In the periodic regime, the regions of period-one oscillations are identified via bifurcation diagrams and peak amplitude curves/maps, where the dependence on some key parameters is systematically studied. In the CW regime, we explore the high-frequency polarization modulation. In particular, double peak response curves are found when spin-VCSELs are pumped with a certain polarization degree and the RO frequency related peak in the frequency response curve is extremely sensitive to the variation of the polarization degree, which leads to rich modulation dynamics in spin-VCSELs. Additionally, the effects of the spin relaxation rate on the polarization modulation bandwidth are illustrated by using two-parameter bandwidth maps. These findings help us better understand the underlying high-frequency dynamics of the optically pumped spin-VCSELs.

Biography

Nianqiang Li received the B.S. degree in communication engineering and the Ph.D. degree in optoelectronics from Southwest Jiaotong University, China, in 2008 and 2016, respectively. His thesis work concerned nonlinear dynamics of semiconductor lasers and its applications to secure communications and random number generation. From 2013 to 2014, he was a Visiting Scholar with the Georgia Institute of Technology (Georgia Tech), USA. From 2016 to 2018, he was with the School of Computer Science and Electronic Engineering, University of Essex, as a Postdoctoral Researcher focusing on a collaborative EPSRC funded project in U.K. From May, 2018 to December 2018, he was with the School of Electrical Engineering and Computer Science, University of Ottawa, Canada, working on microwave photonics. He began to work in Soochow University as a full professor since January, 2019. He has authored or co-authored more than 70 peer reviewed journal papers. He is currently working at School of Optoelectronic Science and Engineering, Soochow University, Suzhou, China. His current research mainly focuses on the area of the laser dynamics, chaos-based communication and random number generation, and microwave photonics. He is an Associate Editor of the IEEE ACCESS.