Electrically Pumped Single Transverse-Mode Coupled Waveguide Lasers by   Parity-time (PT) Symmetry
  We demonstrate single transverse-mode operation of broad-area coupled waveguide lasers enabled by parity-time (PT) symmetry. The PT symmetric laser operates on coupled waveguide cavities with electrically tuned gain and loss. Such counterintuitive waveguide design enables PT symmetric breaking, causing unique mode selection and ultimately enabling single mode operation. By electrically tuning the loss in the loss region of the coupled waveguide cavity, several different PT-symmetric regimes are analyzed theoretically, and the corresponding PT symmetric phase transition is demonstrated experimentally in the coupled waveguide laser. 
Ruizhe Yao, Chi-Sen Lee, Viktor Podolskiy, and Wei Guo
physics.optics