Single Transverse-Mode Semiconductor Laser Arrays by Parity-Time Symmetry Breaking

Electrically pumped semiconductor laser array operating in the fundamental mode is of vital importance. In general, the competition of multiple transverse modes in the laser array leads to spatiotemporally unstable and degradation of beam quality. In this letter, we propose and experimentally demonstrate electrically pumped single transverse-mode semiconductor laser arrays by exploiting the concept of parity-time symmetry, which is insensitive to fabrication and frequency detuning. Laser arrays composed of four, six and ten-ridge gain lattice have been fabricated, and single transverse-mode operations are observed from the spectral response and far-field radiation. Insensitivity to the fabrication have also been experimentally demonstrated by varying the gap from $1.06 \mu \text{m}$ to $1.42 \mu \text{m}$ . The emission power of PT-symmetric laser arrays composed of a four-ridge gain lattice is about five times higher than that of the single-ridge laser with the same current density.