Luminescent Polymer Fibers for Light Amplification and Lasing
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Luminescent Polymer Fibers for Light Amplification and Lasing Takeyuki Kobayashi1, Werner J. Blau1, Hartwig Tillmann2 and Hans-Heinrich Hörhold2 Materials Ireland Polymer Research Centre, Department of Physics, Trinity College Dublin, Dublin 2, Ireland 2 Institut für Organische Chemie und Makromolekulare Chemie, Friedrich-Schiller-Universität Jena, Humboldtstraße 10, D-07743, Jena, Germany 1
ABSTRACT We report on the fabrication of step index polymer optical fibers that use a novel conjugated polymer and fluorescent stilbenoid compounds for lasing and amplification applications in the blue-green regions. The green-emitting polymer, Thianthrene-MEH-PPV, and the blue-emitting compounds, 1,2-bis(4-diphenylaminophenyl)-ethylene and 1,4-bis(4-diphenylamino-styryl)-benzene, are designed for the blue-green region of the spectrum and have very high quantum yields and large Stokes shifts. Significant spectral narrowing and superlinear increase of output intensity are observed under photoexcitation at 355 nm, which are indicative of the occurrence of amplified spontaneous emission. By gain spectroscopy, a high gain coefficient of 36 cm-1 at 494 nm has been obtained for the 1,4-bis(4-diphenylamino-styryl)-benzene-doped fiber when it is transversely photoexcited at 12 mJ/cm2. INTRODUCTION Over the past decade, there has been increasing interest in the development of organic lasers [1-3]. Polymeric gain media offer several advantages such as wide spectral coverage by chemical tailoring of structure, processability that permits fabrication of devices of virtually any shape, and potentially very low cost. Amplified spontaneous emission (ASE) and lasing characteristics of both small molecular weight compound-doped polymers and conjugated polymers with a variety of device structures have been investigated. These structures include Fabry-Perot microcavities, microspheres,
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(c) B180 Figure 1. Molecular structure: (a) 1,4-bis(4-diphenylamino-styryl)-benzene (SP35), (b) 1,2-bis(4-diphenylaminophenyl)-ethylene (SP48) and (c) Thianthrene-MEH-PPV. C8.10.1
microcylinders, distributed Bragg reflector and distributed feedback waveguides and photonic bandgap resonators [4]. Waveguide structures provide long gain length and optical confinement, which offers reduction of lasing threshold, required for efficient lasing. Polymer fibers are especially attractive due to their symmetric output beam profile and adaptability to optical fiber-based communication systems. There have been, however, few reports on polymer fiber lasers to date. The pioneering work by Muto et al. showed the first light amplification in step index polymer fibers with 2 cm length [5]. Efficient and photostable lasing was demonstrated from graded index polymer optical fibers with 5 cm length [6]. In both studies, commercially available laser dyes were used. In this paper, we report on the fabrication of step index polymer optical fibers that use a novel green-emitting PPV-family conjuga
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