Evolution of very small lasers

Quest for the smallest possible laser has been intensely on-going over several decades, attracting scientists in the semiconductor laser community. The evolution of small semiconductor lasers, from VCSEL to photonic crystal laser and 1-D nanobeam laser, is reviewed and recent efforts on the ultra-low threshold small lasers are to be discussed. The potentials and limits of the very small metallic lasers and resonators will be also be addressed.