Multiple-soliton dynamic patterns have been observed experimentally in an erbium-doped fiber ring laser with graphene as a saturable absorber. Under relatively low pumping power we have obtained disordered multiple-solitons, bunched solitons and high order harmonic mode locking by adjusting the orientation of the polarization controllers. With increased pumping power, we have also observed flow of solitons. We have experimentally investigated in detail the conditions under which these patterns form.

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model and the extended Hubbard model (EHM), we analyze the scattering and combination in conjugated polymers of two polarons with the same charges and parallel or antiparallel spins using a nonadiabatic evolution method. Results show that collisions between the two same charge polarons with parallel spin are essentially elastic due to strong Pauli repulsion, whereas the two same charge polarons with antiparallel spins can combine into a singlet bipolaronic state. The dynamics of bipolarons on two coupled polymer chains and at the interface of a polymer/polymer heterojunction are discussed in detail. This knowledge will serve to understand the dynamics of the system when many polarons are created in the system, e.g., by electroluminescence.

Both polarons and excitons, which are composite particles with internal lattice structure, play an important role in the transport and light-emitting properties of conjugated polymers for the use in, e.g., polymer based light-emitting diodes (LEDs). The scattering and recombination processes between a triplet exciton and a polaron are investigated using a nonadiabatic evolution method based on an extended Su-Schrieffer-Heeger model including interchain interactions. The results show that an excited polaron state can be formed, besides a triplet exciton is converted into a singlet exciton by the polaron. Moreover, the yields of both the singlet exciton and the excited polaron states increase with increasing interchain coupling strength. The excited polaron is luminescent due to radiative decay as is the singlet exciton. Therefore, our results indicate that the quantum efficiency of polymer LEDs could be enhanced by polaron-exciton recombination.

We demonstrate a passive mode-locked Er:Yb doped double-clad fiber laser using a microfiber-based topological insulator (Bi(2)Se(3)) saturable absorber (TISA). By optimizing the cavity loss and output coupling ratio, the mode-locked fiber laser can operate in L-band with high average output power. With the highest pump power of 5 W, 91st harmonic mode locking of soliton bunches with average output power of 308 mW was obtained. This is the first report that the TISA based erbium-doped fiber laser operating above 1.6 μm and is also the highest output power yet reported in TISA based passive mode-locked fiber laser.

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model and the extended Hubbard model (EHM), the scattering and combination of oppositely charged bipolarons in conjugated polymers are investigated using a nonadiabatic evolution method. On the basis of this physical picture, bipolarons can scatter into a singlet biexcitonic state, in which two electrons and two holes are trapped together by a lattice distortion. This biexcitonic state can emit one photon to an exciton state, which can subsequently decay to the ground state. The results indicate that the scattering and combination of oppositely charged bipolarons may provide guidance for improving the internal quantum efficiency for electroluminescence to as high as 75% in polymer light-emitting diodes.