  Polymer micro- and nano-fibers, made of organic light-emitting materials with
optical gain, show interesting lasing properties. Fibers with diameters from
few tens of nm to few microns can be fabricated by electrospinning, a method
based on electrostatic fields applied to a polymer solution. The morphology and
emission properties of these fibers, composed of optically inert polymers
embedding laser dyes, are characterized by scanning electron and fluorescence
microscopy, and lasing is observed under optical pumping for fluences of the
order of 10^2 microJ cm^-2. In addition, light-emitting fibers can be
electrospun by conjugated polymers, their blends, and other active organics,
and can be exploited in a range of photonic and electronic devices. In
particular, waveguiding of light is observed and characterized, showing optical
loss coefficient in the range of 10^2-10^3 cm^-1. The reduced size of these
novel laser systems, combined with the possibility of achieving wavelength
tunability through transistor or other electrode-based architectures embedding
non-linear molecular layers, and with their peculiar mechanical robustness,
open interesting perspectives for realizing miniaturized laser sources to
integrate on-chip optical sensors and photonic circuits.
