  One of the most fascinating predictions of the theory of general relativity
is the effect of gravitational lensing, the bending of light in close proximity
to massive stellar objects. Recently, artificial optical materials have been
proposed to study the various aspects of curved spacetimes, including light
trapping and Hawking's radiation. However, the development of experimental toy
models that simulate gravitational lensing in curved spacetimes remains a
challenge, especially for visible light. Here, by utilizing a microstructured
optical waveguide around a microsphere, we propose to mimic curved spacetimes
caused by gravity, with high precision. We experimentally demonstrate both
far-field gravitational lensing effects and the critical phenomenon in close
proximity to the photon sphere of astrophysical objects under hydrostatic
equilibrium. The proposed microstructured waveguide can be used as an
omnidirectional absorber, with potential light harvesting and microcavity
applications.
