Lasing And Directional Emission From Novel Microcavity Lasers

Microcavity is an optical resonator in micron or sub-micron size, which can be used as micro-sized laser source or optical communication device. It confines lights inside a small volume by reflection, total internal reflection, scattering, or diffraction at the interface. As the volume of cavity is decreased to micron size, only one or several optical modes can exist inside the resonator. Thus the spontaneous emission of atom or molecule inside the cavity will be altered and laser emission can occur as well.This thesis mainly emphasizes on the lasing actions of various microcavities. We have designed and fabricated several types of micro-sized resonators such as planar microcavity, surface corrugated waveguide random laser, planar random microcavity, and whistle like microdisk. Using these devices, we have successfully realized the directional emission and achieved low threshold requirement of micro-sized laser source.This thesis focuses on the following aspects:First, we have introduced a new method to fabricate planar microcavity with sol-gel technique. Using this method, we have successfully fabricated distributed Bragg reflector without crack under low temperature (150°C). As the operation temperature is very low, the organic planar microcavity could be fabricated with this new sol-gel method. After the synthesis of organic planar microcavity, its photoluminescence properties are measured and simulated with transfer matrix method.Second, from the random lasing action inside optical waveguide, we have shown the effects of corrugated waveguide surface on the generation of random lasers. At the same time, the corrugated system is simplified to one-dimensional multilayer by effective refractive index of waveguide, and its modes and field distribution are simulated with transfer matrix method.Third, we have designed a new structure named planar random microcavity, which combined planar microcavity and random lasers. Using the confinement of random medium on the transverse plane and planar microcavity in the vertical direction, we have successfully reduced the threshold of random lasers and obtained directional laser emission (1.5-1.6 degree). Comparing the planar random microcavity with vertical cavity surface emission laser, the laser resonance inside was physically explained. By infiltrating liquid crystals inside the planar random microcavity, we also obtained, for the first time, the tunable random lasers emission.Finally, we have fabricated an organic/inorganic hybrid whistle like microdisk by wet etching and sol-gel technique. Under laser pumping, we obtained unidirectional laser emission from this whistle like microdisk, which proves the Yale theory about unidirectional emission of spiral microdisk well.