We demonstrate a way of light harvesting in integrated microfluidic chips fabricated by femtosecond laser micromachining. The architecture consists of waveguide arrays fabricated in the vicinity of the microchannel filled with a fluorescent organic solution (e.g., polyfluorene solution). Amplified spontaneous emission from the microchannel is efficiently coupled by the waveguides to the outside of the chip.
Femtosecond laser based micromachining technologies have the inherent capability of producing elements in 3D. Their
ability of rapid prototyping can be exploited to develop novel Optofluidics devices. Microfluidic channels were
fabricated and integrated with optical waveguides using a single femtosecond laser. Optically pumping the microchannel
filled with polyfluorene solution and by dispersing nanoparticles in the solution, random lasing in the microchannel is
obtained. We demonstrate a novel approach to organic photonic devices, where the unique properties of a conjugated
polymer in solution are exploited in a microfluidic configuration in order to produce easy-to-integrate photonic devices.
We fabricated polymer optical fiber (POF) amplifiers operating between 440 and 480 nm, using POFs doped with a series of fluorene oligomers, including tri-, penta-(9,9-dioctylfluorene) and hepta-(9,9-dihexylfluorene). The gain properties of pure oligofluorene films demonstrate gain coefficients on the order of 250 dB/cm and amplified spontaneous emission thresholds between 1 and 8 µJ cm-2, significantly lower than other fluorene gain media. The optical and morphological characteristics of PMMA thin films doped with the oligomers demonstrate that the oligomers are largely isolated within the PMMA. The optical and gain properties of POFs produced using an adapted preform-drawing technique and doped with the oligofluorenes provide gain values on the order of 0.07 dB for 2 mm of doped POF. The oligofluorenes are largely isolated within the POFs, paving the way for all optical gain-switching.
Using ultrafast pump-probe and pump-push-probe spectroscopy we highlight evidence of monodimensional photophysics coming from isolated chains of poly(9,9-dioctylfluorene) (PFO). We identify a large gain band with peak value of 2600 db/cm.
By exploiting the peculiar one-dimensional physics of the isolated chain, we envisage a novel principle for ultrafast all-optical gain switching. Experiments suggest that the expected maximum rate of on-off switching over a broad wavelengths range (around 100 nm) can be as high as 300 GHz with large modulation depth.
Poly(9,9-dicotylfluorene)(PFO) exhibits very good, non- dispersive hole transport but very poor electron transport. To achieve the maximum efficiency in a PFO light emitting diode it is important to balance the electron and hole currents. Here we report three schemes to achieve this in single layer devices. Firstly, by using different treatments to change the work function of the indium tin oxide anode contact, the hole current can be varied by up to 4 orders of magnitude, thus allowing it to be adjusted to the same level as the electron current. Secondly, the hole mobility can be decreased by doping PFO with a hole trapping, emissive material. Upon the addition of 5% by weight of a red-emitting tetraphenylporphyrin, hole transport in PFO becomes as highly dispersive as electron transport, resulting in a decrease in the current for a given applied bias but an increase in the electroluminescent efficiency. Thirdly, the electron mobility can be increased by doping PFO with an emissive, electron transporting material. The electroluminescent polyfluorene copolymer poly(9,9-dioctylfluorene-co-benzothiadiazole (BT) exhibits strong but dispersive electron transport. PFO devices doped with BT show very high efficiencies, high peak brightnesses and very low turn on voltages.