Microcavity lasers have been attracting much more attention recently. Microdisk lasers represent a novel class among them. The disk thickness is typically only a half of an optical wavelength in the materials. Whispering gallery modes near the disk edge account for the low loss resonator modes. InGaAs/InGaAsP MQW microdisk lasers based on this disk resonator were fabricated by using standard photolithography

reactive ion etching (RIE) and wet chemical etching. The MQW materials were grown on InP substrates by gas source MBE technique. The diameters of the disk laser we had made were 8μm

4.5μm and 2μm

respectively. The optical properties of the disk were characterized by optical pumping at liquid nitrogen temperature. The lasing threshold of the disk with a diameter of 2μm was only about 3μW when pumped by 514.5nm line of Ar ion laser. To our knowledge

this threshold of 3μW is the lowest one up to now. Multiple mode lasing

mode chirping and output saturation were investigated when pumped at high optical pump density. It was observed that the structure of the photoluminescence spectra became sophisticated with increasing the pump power. New lasing peaks appeared and became dominated in the spectra. It was also observed that the intensity of lasing lines became saturated with increasing the pump power. The linewidth of lasing peak was of the order of about 1.3nm. It was also observed that microdisk lasers showed anomalous linewidth behavior compared with ordinary semiconductor laser. This characteristic was usually explained with many-body effect induced by the non equilibrium carrier distribution when optically pumped.