Waveguiding properties of fiber-shaped aggregates self-assembled from thiacyanine dye molecules

The waveguiding properties of the fiber-shaped aggregates self-assembled from the thiacyanine (TC) dye in solution were investigated by spatially resolved fluorescence microscopy. The TC fibers transferred onto a glass substrate were excited by a focused laser beam. The spectra of the outcoupled light from the fiber end were recorded as a function of the distance between the laser spot and the fiber end. The spectral images in a false-color intensity scale constructed from the outcoupled light spectra exhibited the waveguiding properties of the fibers well. The optical losses for the wavelength range over the entire emission band (470-620 nm) were quantitatively determined. It was found that the fibers have a cutoff wavelength at similar to 480 nm, below which the light is not guided, and these fibers act as low-loss waveguides for the wavelength range of 530-600 nm. The spectral images also revealed that the TC fiber functions as an optical cavity (Fabry-Perot cavity) by the recurrence of the guided light due to the reflection at the end facets of the fiber.