Intro -- List of Publication -- Abstract -- 1 Introduction -- 2 General theory -- 2.1 Light Propagation -- 2.2 Optical Waveguide -- 2.3 Organic Semiconductor -- 3 Organic Laser -- 3.1 Working Principle -- 3.2 Distributed Feedback (DFB) Laser -- 3.3 Literature Overview -- 4 Experimental Methods -- 4.1 Material -- 4.2 Fabrication Methods -- 4.3 Measurement Methods -- 5 Result -- 5.1 Sample Outlook -- 5.2 Material Characteristics of Samples Doped with DifferentConcentrations -- 5.3 Material Characteristics of Samples Doped with DifferentDyes -- 5.4 Lasing Properties of Different Designs -- 5.5 Lasing Tuning -- 6 Conclusion -- Acknowledgements -- Abbreviations -- List of Figures -- Bibliography.