  Development of artificial materials exhibiting unusual optical properties is
one of the major strands of current photonics research. Of particular interest
are soft-matter systems reconfigurable by external stimuli that play an
important role in research fields ranging from physics to chemistry and life
sciences. Here, we prepare and study unconventional self-assembled colloidal
optical waveguides (CWs) created from wavelength-size dielectric particles held
together by long-range optical forces. We demonstrate robust non-linear optical
properties of these CWs that lead to optical transformation characteristics
remarkably similar to those of gradient refractive index materials and enable
reversible all-optical tuning of light propagation through the CW. Moreover, we
characterize strong optomechanical interactions responsible for the CW
self-assembly; in particular, we report self-sustained oscillations of the
whole CW structure tuned so that the wavelength of the laser beams forming the
CW is not allowed to propagate through. The observed significant coupling
between the mechanical motion of the CW and the intensity of light transmitted
through the CW can form a base for designing novel mesoscopic-scale photonic
devices that are reconfigurable by light.
