Novel Polymer Gratings Applied In Organic Semiconductor Lasers

Organic/polymer luminescent material is a kind of superior gain material with high gain coefficient and low self-absorption coefficient, which could be applied in the fabrication of organic semiconductor lasers. In order to lower lasing threshold to realize electrically driven lasing, low-loss organic resonator should be made. Distributed feedback(DFB) structure is believed as one of the most promising way. In this thesis, a new method is proposed to fabricate polymer DFB gratings via UV photopolymerization, and the characteristics of these novel polymer gratings are studied.A new prescription of photopolymer is designed, and a proper solvent is chosen. This photopolymer is sensitive to 325nm wavelength, and it can be fabricated into high-quality polymer films via spin-coating technology.A complete procedure of technology to fabricate polymer DFB gratings is set up. Specialities of refractive index modulation and surface relief of these novel polymer DFB gratings are studied. Experimental results show that the refractive index modulation can reach about 0.010; and the depth of surface relief is low to about 0.7~12.4nm, which will be lower than 1nm in the gratings with 200~400nm period(according to the first-order and second-order DFB grating period of organic semiconductor lasers).A simple theoretical model is built to analysis the effect of light scattering by the inside defects of polymer films. Quality of the polymer film should be improved and defect density should be reduced in order to improve the refractive index modulation of short-period DFB gratings. Characteristics of surface relief of polymer DFB gratings are also analyzed, illustrating that to reduce the surface relief, monomer and polymer binder with high-velocity migration should be used.Results of this thesis indicate that the novel polymer DFB gratings fabricated via UV-photopolymerization can achieve high refractive index modulation and low surface relief. Since this method has obvious predominance over other fabricating methods, it is believed to have promising application future in the organic semiconductor lasers.