Scale Effect of Fluorescent Waveguide in Organic Micro-Materials: A Case Study Based on Coumarin Microfibers

摘要： In the past decades, the rapid development of integrated optoelectronic devices has motivated the study of the miniaturized optoelectronic components, among which the micron or sub-micron waveguides have attracted a great deal of attention. In this regard, the waveguides made of organic materials show many advantages, such as intense fluorescence, tailor-made structure and facile crystallization. The waveguide ability was usually expressed in the form of the optical loss coefficient (denoted by <), which is mainly determined by the materials of the waveguide, and relatively low < usually corresponds to less optical loss and better propagation. The value of < was usually determined by the exponential fitting of the curves of the guided intensity (Itip/Ibody) versus the waveguiding distance (x). When the sectional size of the waveguide was down/close to the wavelength of the exerted light, the traditional evaluation is no longer valid, since < is also influenced by the diameter of the waveguide. For example, silica fibers with diameter more than one micron allow multimode waveguiding of visible and infrared light, while those with diameter of sub-micron allow single-mode operation. In case of organic waveguide, the situation becomes complicated, especially for those with size close to micron and sub-micron (range for majority organic waveguides). Except for the refraction index, the sectional size and the auto-absorption within the waveguide should also be considered. Models that accurately describes the waveguiding ability are highly demanded, but still dangling with no clues.