Evolution of small lasers and resonators

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