Continuous melt processing of all-polymer distributed feedback lasers† Hyunmin Song, b Kenneth Singer, * a Joseph Lott, b Yeheng Wu, a Juefei Zhou, a James Andrews, c Eric Baer, b Anne Hiltner b and Christoph Weder‡ b Received 11th May 2009, Accepted 11th June 2009 First published as an Advance Article on the web 15th July 2009 DOI: 10.1039/b909348f Novel processing techniques for low-cost production of photonic devices could open up new applications for functional polymer systems. To this end, we have used multilayer coextrusion in a continuous melt process to fabricate large-area polymeric nanolayer films for optically-pumped all-polymer distributed feedback (DFB) surface-emitting lasers. Each laser film consists of hundreds of alternating layers of two transparent polymers with different refractive indices, of which one contains a laser dye. The resulting DFB lasers emit at defect states and show efficiencies as high as 8% and threshold fluences as low as 100 mJ/cm 2 . Introduction The rapid development of organic optoelectronic materials and devices is revolutionizing modern electronics. 1 Flexible, high- performance polymer thin-films have begun to replace inorganic semiconductors in photovoltaic cells, 2 transistors, 3 light emitting diodes, 4 lasers 5–9 and other devices. Because polymers are, in principle, amenable to large-area, low-cost fabrication methods and because their properties can be readily tailored, polymeric materials have received considerable attention for laser devices. While the possibility for simple melt processing was much her- alded, much more complex fabrication protocols are generally used. All-polymer distributed feedback (DFB) lasers have, for example, been fabricated using spin-coating, molding and embossing techniques. 6–11 We recently introduced all-polymer distributed Bragg reflector lasers, which were assembled by laminating two co-extruded polymeric Bragg mirrors on either side of a compression-molded, dye-doped polymeric gain medium. 12,13 We report here on the fabrication of optically- pumped, all-polymer, surface-emitting, distributed feedback dye lasers by multilayer co-extrusion in a single roll-to-roll process. The method, which allows the production of multilayer films with hundreds of alternating nanometer-thin layers, 14,15 capitalizes on the melt-processibility of polymers and is capable of rapidly producing large areas of high-quality laser films in a one-step roll- to-roll melt process. These flexible thin-film devices can be lami- nated onto diode pump lasers or photonic circuits for various applications. Roll-to-roll processing by multilayer coextrusion of active photonic and electronic devices such as wavelength-agile polymer lasers could open new approaches to display, sensing, optical communication, and data storage technologies. A DFB laser consists of a single one-dimensional periodic dielectric structure that also serves as the gain medium. The periodic dielectric structure is a photonic crystal that provides the necessary feedback by concentrating the emitted optical mode. The one-dimensional index of refraction variation causes a reflection band or photonic bandgap, whose wavelength and shape are determined by the dimensions of the dielectric structure, the refractive indices, and the number of periods. As a photonic crystal, the associated density of photonic states in a perfectly periodic structure vanishes in the reflection band and is highly enhanced at the band edge. This enhanced density of states provides the necessary laser feedback. Therefore, emission in a perfectly periodic DFB laser occurs at the reflection band edge. 16 Experimental The multilayer films were coextruded at 250  C using a contin- uous layer-multiplying process (Fig. 1). Low-density poly- ethylene (LDPE 6201 provided by the Dow Chemical Company) skin layers were added to both sides of the multilayer films Fig. 1 Schematic of the co-extrusion process. a Department of Physics, Case Western Reserve University, Cleveland, OH, 44106, USA. E-mail: kenneth.singer@case.edu b Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH, 44106, USA c Department of Physics and Astronomy, Youngstown State University, Youngstown, OH, 44555, USA † This paper is part of a Journal of Materials Chemistry theme issue on organic non-linear optics. Guest editor: Seth Marder. ‡ Current address: Adolphe Merkle Institute and Fribourg Center for Nanomaterials, University of Fribourg, CH-1700 Fribourg, Switzerland. 7520 | J. Mater. Chem., 2009, 19, 7520–7524 This journal is ª The Royal Society of Chemistry 2009 PAPER www.rsc.org/materials | Journal of Materials Chemistry