  Curved reflective mirrors play an indispensable role in widely-employed
Cassegrain-type optics, which consequently are inevitably bulky, and thus
neither integratable nor well extendable. Through substituting geometric phase
based reflective metasurfaces for curved mirrors, here a planar Cassegrain-type
Schwarzschild objective is obtained, with both the focusing and imaging
functionalities experimentally verified. The planar reflective objective
achieved is intrinsically free of residual light and thus imposes less
stringent restrictions on illuminating light and nanofabrications compared to
its refractive counterpart. Our planar Cassegrain-type designs can potentially
reshape and simplify the core components of the microscope and telescope
systems working at a broadband spectral range, and thus opens new avenues for
designing compact imaging systems.
