Optical properties of planar polymer waveguides doped with organo-lanthanide complexes

AbstractLanthanide complexes, Eu(dbm) 3 (Phen), [Et 4 N][Eu(nta) 4 ] and Er(dbm) 3 (Phen), are employed as luminescent dopants within planarwaveguides based on a UV-processable fluorinated polymer material. Thin films doped with each of the complexes are fabricated andtheir spectroscopic properties investigated in detail. The films act as low loss multi-mode planar waveguides capable of guiding visibleand near infrared light emitted following optical excitation of the lanthanide dopants. Judd–Ofelt parameters are calculated for the euro-pium complex dopants and effects of the polymer host environment on the photophysical properties of the chelates are identified. Theradiative properties of the europium complexes are also determined viz. their potential for use in optical amplification applications. 2006 Published by Elsevier B.V. PACS: 78.20. e; 42.82.Et; 81.05.Lg; 42.70.JkKeywords: Lanthanide complex; Europium; Erbium; Photoluminescence; Polymer waveguide 1. IntroductionRare earth ions have been extensively studied withregard to their photophysical behaviour in a variety ofadvanced materials [1]. Their unique radiative propertieshold great promise for a broad range of technologies.These applications encompass not only phosphors for fluo-rescent lighting tubes and colour television displays, butalso light emitting diodes [2,3], lasers and optical amplifiers[4]. Within the field of optical communications in particu-lar, conventional telecommunications amplifiers that oper-ate at infrared wavelengths, e.g., erbium doped fibreamplifiers (EDFAs), exploit optical path lengths of severalmeters for amplification. Also, with improvements in thepropagation loss characteristics of plastic optical fibres(POF) at visible wavelengths, the development of analo-gous lanthanide doped plastic optical fibre amplifiers forsignal regeneration within data communications networksis underway [4,5]. In the future, there will likely be a needfor integrated glass and/or polymer waveguide based opti-cal amplifiers that will operate across the visible and nearinfrared spectral range and will be compatible with ‘‘on-chip’’ switches, splitters and multiplexers [6]. However,on-chip device integration is very spatially restrictive, typ-ically allowing an optical path length of only a few centime-tres. Consequently, substantial optimisation of theperformance of lanthanide doped materials for waveguidebased optical amplification is now required.Polymers have attracted significant attention as wave-guide materials due to relatively low costs, favourablematerials properties and potential ease of processingthrough compatibility with novel fabrication methods suchas hot embossing and soft lithography. The availability ofUV cross-linkable polymers also offers the possibility of