  This thesis contributes to the field of gravitational lensing (GL) and
observational cosmology. We discuss the use of gravitational lensing as a tool
in search of exotic objects in the Universe. In the next chapter the
concordance of an alternative cosmological model with the current gravitational
lensing observations is explored and also a non-minimally coupled effective
gravity theory that supports non-topological solitonic solutions is considered.
In the last chapter we study propagation of light in strong gravitational
field. Using geometrical optics approach we show that massless particles with
spin deviate from the geodesic motion. We demonstrate that the velocity of
photon propagating in a Kerr black hole background remains subluminal.
