Final Report Summary - DISCANT (High-energy dissipative soliton dispersion-managed fibre laser based on carbon nanotubes) The project DISCANT is focused on knowledge transfer in the field of fibre lasers from the Fellow to the EU host. We focus on the development and application of dispersion-managed dissipative soliton fibre lasers with high energy. The overall research aim of the project is to develop new concepts, techniques and approaches to the new design of fibre lasers based on a transfer of the methods of nonlinear science into the field of optical engineering.Dissipative solitons can be stable at much higher powers than ordinary solitons, making them promising for the creation of high-power, short-pulse sources. Dissipative soliton lasers can reach megawatt pulse powers if they are made from a fibre with a large core. This is several times the peak power of solid-state lasers such as the Ti:Sapphire lasers that currently dominate ultrafast science. Dissipative solitons actively studied across the globe will have a significant impact on the future applications of ultrashort pulses. Such high-energy ultrashort pulses from laser oscillators are required for physics, chemistry, biology, medicine and dentistry. They will enable a variety of nonlinear bio-imaging techniques, the generation of terahertz wavelengths, measurements of ultrafast phenomena and high-precision materials processing. We propose here to extend the theory of dispersion-managed (DM) solitons to dissipative systems with a focus on mode-locked fibre lasers.Work package 1 is focused on develop a new method for the propagation equations which includes the essential discrete components that are responsible for large intra-cavity pulse fluctuations. Such an approximate approach will be verified by extensive direct numerical modelling demonstrating the validity of the model. The numerical codes were developed in Matlab software and the solutions were calculated applying split-step technique. The parameters were chosen close to the experimental system. The work package was done in collaboration with researches from ultrafast laser group in Bilkent University. Work Package 2 is to fabricate and characterize single walled carbon nanotube (SWNT) saturable absorber. A new type of SWNT saturable absorber, i.e. SWNT/P3HT film has been fabricated. P3HT molecules can interact sufficiently with SWNTs to penetrate the SWNT bundles, thus reducing the van der Waals interaction between the SWNTs. Therefore, we used P3HT to separate bundles of SWNTs and facilitated the optimum saturable absorption effect efficiently. Additionally, after the preparation of SWNT/P3HT solution, polyamide with desirable optical properties and high heat resistance was chosen as host polymer. The glass transition temperature (Tg) of polyamide (aramid), which is a measure of the heat resistance of the polymer material, is as high as 300 °C, whereas it is 100 and 150 °C for polymethylmethacrylate(PMMA) and polycarbonate(PC), respectively. And using the polyamide film as a base enabled us to realize a self-standing SWNT/P3HT thin film. The aromatic polyamide SWNT film is a new saturable absorber, having both high heat resistance and transparency.Work package 3 is focused on development of femtosecond fibre lasers without bulk dispersion compensators. We have realized an all fibre dispersion-managed passively mode-locked Yb-doped fibre laser based on SWNTs. With optimal net normal cavity dispersion, the output dissipative soliton pulses with strong chirp have been obtained. As a result, the oscillator generated 8.7 ps pulse with a spectral bandwidth of 17.6 nm, which is strongly chirped. And through further compression outside the cavity, shortest pulses to 118 fs have been attained.Work package 4 is investigation of the noise performance of a dissipative laser and construction of wideband tunable fibre laser systems based on dissipative solitons. We have shown that different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tunable over a much broader range of wavelengths than other systems. SWNTs show large optical nonlinearity, ultrafast carrier relaxation time and high damage threshold. The variation of nonlinear absorption is determined by the number of tubes in resonance with the incident light. However, even for a wavelength detuning of up to 200 nm from the peak resonance, appreciable saturable absorption can still be observed. This implies great potential for wideband tunable lasers.Work Package 5 Tilted fiber gratings have unique polarization properties, which can be utilized for mode-locked fiber lasers. 45°-tilted fiber grating (45°-TFG), which taps out the s-light and propagates the p-light based on the Brewster’s law, can be used as a new type of in-fiber polarizer for mode-locking. Our results show that 45°-TFG can replace generally used polarizer in mode-locked fiber lasers based on nonlinear polarization rotation, and taking the advantage of the in-fiber essence, 45°-TFG can be easily integrated into the fiber laser cavity with very short additional length, which pioneers a new way to control the dimension and enhance the fundamental repetition rate for mode-locked fiber laser. Additionally, the large-angle tilted fiber grating (LA-TFG) exhibits polarization-dependent loss and polarization-mode splitting. Switchable dual-wavelength Q-switched and mode-locked pulses have been achieved with short and long cavities, respectively. For the mode-locking case, the laser was under the operation of nanosecond rectangular pulses, due to the peak-power clamping effect. With the increasing pump power, the durations of both single- and dual-wavelength rectangular pulses increase. It was also found that each filtered wavelength of the dual-wavelength rectangular pulse corresponds to an individual nanosecond rectangular pulse by employing a tunable bandpass filter. Related documents final1-publishable-summary.doc
