DFB Structures in Electroactive Conjugated Polymers realized by Soft Lithography
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DFB Structures in Electroactive Conjugated Polymers realized by Soft Lithography Erik Moderegger1, Martin Gaal2, Christoph Gadermaier2, Harald Plank2, Emil J.W. List2, Alexander Pogantsch3, Roland Güntner4, Ullrich Scherf4, Günther Leising1 1 AT&S AG, Science & Technology, Fabriksgasse 13, 8700 Leoben, Austria 2 Christian Doppler Laboratory for Advanced Functional Materials, Graz University of Technology & Joanneum Research, Petersgasse 16, 8010 Graz, Austria 3 Institute for Solid-State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria 4 Department of Chemistry, BUGH Wuppertal, Gauss-Straße 20, D-42097 Wuppertal, Germany. ABSTRACT The realization of a polymeric injection laser diode is an important aim in organic electronics. A crucial step towards this goal lies in the understanding and fabrication of feedback structures for lasers. Such feedback structures may be fabricated either in the substrate or directly in the active polymer layer. Soft Lithography has proven itself as a useful tool to pattern a wide variety of materials. Typically one uses elastomeric molds (stamps) to pattern materials and structures whereby dimensions as low as 30 nm can be achieved. Different types of Soft Lithographic processes are applied to produce optical feedback structures for optically pumped laser arrays. INTRODUCTION Many of today’s technological applications, e.g. in telecommunications, science, medicine, optical data storage, materials processing, and consumer electronics, rely on the use of lasers. At present, a variety of laser sources is available, using very different energies, sizes and wavelengths. For small size applications, inorganic semiconductor diode lasers are the candidates of choice. A large part of the visible spectrum, however, is still not available when employing the most commonly used inorganic III-V semiconductor lasers. Conjugated polymers are attractive candidates for the realization of solid-state lasers because of various reasons: Conjugated polymers can be easily deposited on any type of substrate and there are conjugated polymers, which emit over broad ranges of the visible spectrum. In a diode configuration, it is also feasible to pump them electrically. Upon photopumping a conjugated polymer above a threshold value optical gain via stimulated emission is observed. When light travels down a waveguide spontaneously emitted light is amplified by stimulated emission. For this amplified spontaneous emission (ASE) process to happen i) the refractive index of the polymer must be higher than the one of the substrate and ii) the polymer film has to be thick enough to support waveguiding [1]. When an optical feedback is provided for the emitted light in the active medium, the emission becomes coherent and lasing action can be observed.
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The first laser-like emission in a solid conjugated polymer was demonstrated in 1996 [2]. Since then, optically pumped polymeric lasers in diverse configurations and using different conjugated polymers have been reported. For a recent
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