A novel approach to fixing dynamic instabilities in laser arrays with non-Hermitian coupling
A novel approach to fixing dynamic instabilities in laser arrays with non-Hermitian coupling lead image
The complex dynamical behavior of coupled semiconductor laser-array systems makes them as intriguing for photonics applications as they are challenging. These laser systems are known to undergo a number of hard-to-combat dynamical instabilities that arise from supermode competition and slow-carrier dynamics. Now, in APL Photonics, researchers report demonstrations that show that using non-Hermitian coupling engineering, inspired by recent non-Hermitian photonics applications for controlling laser dynamics, can help these semiconductor systems realize stable-laser operation.
Concepts in non-Hermitian photonics provide a virtual field to test non-Hermitian scattering potentials and quantum-phase transitions, and have evolved to provide new tools for sculpting and controlling the movement of light. The researchers claim these concepts can specifically be used to find a solution to a relatively old laser science problem: forcing stable supermode emission in coupled semiconductor laser arrays.
The authors used a standard rate equation model describing the dynamics of semiconductor laser-arrays arranged in a ring. With this description, they numerically and analytically tested their use of non-Hermitian coupling engineering to combat the onset of dynamical instabilities and force synchronous emissions. They closely examined two types of common “nearest-neighbor” non-Hermitian coupling schemes: symmetric-but-complex mode coupling (type I); and asymmetric-mode coupling (type II).
For type-I coupling, the theoretical lasers emitted in phase. For type-II coupling, the lasers emitted with π/2 phase slips between adjacent lasers, resulting in a vortex far-field beam emission carrying orbital angular momentum.
According to the researchers, the demonstrations with type-II coupling, in particular, show that the scheme may be a valuable tool in laser-array design for combating laser instabilities and resonance-frequency disorder caused by manufacturing imperfections. They expect their results will stimulate further theoretical and experimental studies.
Source: “Mitigation of dynamical instabilities in laser arrays via non-Hermitian coupling,” by S. Longhi and L. Feng, APL Photonics (2018). The article can be accessed at https://doi.org/10.1063/1.5028453 .
