Design and characterisation of blue polymer lasers

• Main Author: Wellinger, Thomas
• Other Authors: Bradley, Donal D. C.
• Published: Imperial College London 2010
• Subjects: 535
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.526341

Semiconducting polymers have attracted considerable attention as novel gain materials for laser devices. An important future target in this context is the realisation of a thin- film polymer laser diode. Since inorganic semiconductors are amongst the most important devices in modern optoelectronic technology, there is a lot of interest in achieving electrically pumped laser action in organic semiconductors as a way to broadly tunable lasers covering the whole visible spectrum and producing low-cost laser sources for optical networks. This thesis reports the results of a study on the design and characterisation of optically pumped blue and violet emitting polymer lasers. The laser devices are based on a range of materials belonging to the polyfluorene family of conjugated polymers which generally show efficient, low threshold stimulated emission. For future electrically pumped polymer lasers, a further reduction of the threshold is crucial since a low threshold fluence directly translates into low current densities. The optical properties of in total three polyfluorene copolymers are investigated. Lasers based on one of these copolymers are optically-pumped and emission wavelength tuning is demonstrated by altering both grating period and gain polymer thickness, allowing us to cover a part of the spectral region between the blue and ultra-violet that has not been addressed yet by organic semiconductor lasers. Furthermore, a systematic numerical study of the optical environment on the performance of blue emitting lasers on conducting DFB resonators is presented, which is followed by a demonstration of optically-pumped polymer lasers based on ITO gratings. Finally, the results of a systematic study into optically pumped blue emitting polymer lasers based on circular Bragg (CBR) resonators is reported. An optimised design strategy is implemented and involves matching the grating pro files with the nulls and maxima from the Bessel functions that represent the radial distribution of the fi eld in a circular resonator.