It is found that cooling dramatically changes the waveguiding properties of organic nanofibers of thiacyanine (TC), which function as active waveguides. At liquid nitrogen temperature (T = 83 K), nanofibers with a width of less than 100 nm efficiently propagate fluorescence (λ = 460–480 nm) over their entire length of ∼100 μm, whereas they propagate no fluorescence at room temperature. Moreover, the fluorescence is observed to be transmitted through sharply bent nanofibers with a bend radius of a few hundred nanometers at T = 83 K. We show that these waveguiding properties result from a modulation of the light–matter interaction in the nanofibers by cooling, which leads to a high refractive index and a low extinction coefficient. Our result demonstrates that nanoscale light manipulation with sub-100-nm-width waveguides is possible by simply cooling TC nanofibers to liquid nitrogen temperature, which can be easily accessed.

To fabricate organic nanofibers that function as active optical waveguides with semiconductor properties, a facile procedure was developed to grow single crystalline nanofibers via π–π stacking of the polycyclic aromatic molecule, coronene, through solution evaporation on a substrate. The fabricated nanofibers with millimeter-scale lengths have well-defined shapes, smooth surfaces, and low-defect structures. The nanofibers are demonstrated to function as efficient active waveguides that propagate their fluorescence (FL) along the fiber axis over their entire length. We further demonstrate that the nanofibers can be highly aligned on the substrate when solution evaporation is conducted in a magnetic field of 12 T. The mechanism of the magnetic alignment can be elucidated by considering the anisotropy of the diamagnetic susceptibility of a single coronene molecule and the crystal structure of a nanofiber. Owing to the high degree of alignment, the nanofibers rarely cross each other, allowing for measurement of the waveguiding properties of single isolated nanofibers. The nanofibers propagate their FL of λ > 500 nm with a low propagation loss of 0–3 dB per 100 μm, indicating that the nanofibers function as sub-wavelength scale, low-loss waveguides. Thus, they are promising building blocks for miniaturized optoelectronic circuits.

We fabricated micrometer-scale optical ring resonators by micromanipulation of thiacyanine (TC) dye nanofibers that propagate exciton polaritons (EPs) along the fiber axis. High mechanical flexibility of the nanofibers and a low bending loss property of EP propagation enabled the fabrication of microring resonators with an average radius (rave) as small as 1.6 μm. The performances of the fabricated resonators (rave = 1.6–8.9 μm) were investigated by spatially resolved microscopy techniques. The Q-factors and finesses were evaluated as Q ≈ 300–3500 and F ≈ 2–12. On the basis of the rave-dependence of resonator performances, we revealed the origin of losses in the resonators. To demonstrate the applicability of the microring resonators to photonic devices, we fabricated a channel drop filter that comprises a ring resonator (rave = 3.9 μm) and an I/O bus channel nanofiber. The device exhibited high extinction ratios (4–6 dB) for its micrometer-scale dimensions. Moreover, we successfully fabricated a channel add filter comprising a ring resonator (rave = 4.3 μm) and two I/O bus channel nanofibers. Our results demonstrated a remarkable potential for the application of TC nanofibers to miniaturized photonic circuit devices.Keywords: micromanipulation; nanofiber; organic dye; photonics; ring resonator;

Highly oriented fiber-shaped J-aggregates of pseudoisocyanine (PIC) molecules were prepared by simply growing the aggregates in a narrow glass cell, which allows evaporation of the solution in one direction.

•The mechanism explaining the emission pattern of perylene α-crystals was revealed.•Light propagating in the crystal was coupled to microspheres on the crystal surface.•The pattern is due to the waveguide effect and total internal reflection at the edges.Square single crystals of perylene (α-crystals) exhibit a peculiar emission pattern when excited by a focused laser beam. Fluorescence spots are observed at the point of excitation and at four edges, with the lines connecting the excitation point and edge emissions being perpendicular to the edges irrespective of the excitation position. Two different mechanisms explaining this emission pattern have been proposed so far. Our newly designed experiment and analysis revealed that the involved mechanism features a combination of the waveguide effect and total internal reflection by crystal edges.