Study On Amplified Spontaneous Emission Of Polymer Waveguide

Conjugated polymers are attractive laser gain media materials due to their high photoluminescence efficiencies, large stimulated emission cross section, low fabrication cost and chemically tunable emission wavelength. This dissertation focuses on the study of the amplified spontaneous emission (ASE) characteristics of poly [2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylenevinylene](MEH-PPV) film in order to solve the high threshold and absorption loss from metallic cathode. Some innovative researches as following were carried out.1. Three ways to reduce threshold of ASE from polymer waveguide was studied. The threshold of ASE can be reduced by changing polymer film morphology, inducing orientation of polymer chains and making resonant feedback structure.(1) The enhancements of ASE from MEH-PPV have been achieved via solvent vapor treatment. Correlations between the morphology of the films and the optical performance of polymer-based ASE are investigated. The results show that solvent-vapor treatment can induce self-organization of MEH-PPV into an ordered structure and a smooth surface, leading to the enhanced optical gain. Thus the solvent-vapor treatment is a good method to improve the ASE optical properties of MEH-PPV.(2) An electric field is applied to induce the polarization of MEH-PPV molecule during the process of spin-coating, which cause the orientation of the MEH-PPV chains. The orientated thin film shows lower threshold and higher gain than the normal thin films.(3) ASE from composition of MEH-PPV and TiO2nanocrystals was observed. The role of TiO2nanoparticles plays resonant feedback in improving performance of amplified spontaneous emission.2. The effect of metallic cladding on amplified spontaneous emission of MEH-PPV films was studied. The low optical loss metallic cathode was picked out.(1) Amplified spontaneous emission from an Ag-backed MEH-PPV film controlled by the effect of MEH-PPV film thickness was investigated. The study of ASE characteristics of Ag-backed MEH-PPV films with different thicknesses shows that increasing the film thickness can reduce the quenching which happened in area near to the Ag cladding. (2) The effect of metallic cladding on amplified spontaneous. emission of MEH-PPV films was studied. The results showed that the metallic layer is critical for the ASE of MEH-PPV. The ASE threshold of MEH-PPV films with Ag cladding is11times greater than that of sample without Ag cladding layer. Furthermore, ASE from the samples with Al cladding completely vanishes. ASE recurred when a thin spacer layer, such as a few nanometers of SiO2, is introduced between the MEH-PPV film and the Al cladding. Compared with the Cu or Al electrode, the Ag is most suited as low loss electrode with due to its low refractive index and high reflectivity.3. Electric-field modulation of the ASE in waveguide based on MEH-PPV was studied.(1) The electric-field induced quenching of the ASE at620nm and the spontaneous emission (SE) at580nm was observed which increased. The quenching increases with the rising electric field. The ASE intensity was more effectively quenched than the SE intensity as the field increased. The field dependence of the ASE and the SE intensity can be attributed to field-induced dissociation of photogenerated excitons in the MEH-PPV thin film.(2) ASE from MEH-PPV waveguide with different thickness of SiO2cladding was investigated. Availability refractive index of MEH-PPV waveguide increases with the rising thickness of SiO2cladding. The study of ASE characteristics of MEH-PPV films with different thicknesses SiO2cladding shows that increasing film thickness can reduce lasing threshold of polymer film.(3) ASE in optically pumped MEH-PPV waveguides with Al or Ag electrode was investigated. The results show that Ag electrode can reduce the ASE threshold compared with Al. The electric-field induced quenching of the ASE has been observed. When the electric field reaches8×106V/cm, the ASE intensity in the device with the Ag electrode is nearly shut off.