  We present the design methodology of a light reconfigurable geometric phase
optical element with multi-stable diffraction efficiency states, enabled by a
photoresponsive self-organized chiral liquid crystal. Experimental
demonstration shows the device exhibits a broad diffraction efficiency tunable
range that can be smoothly modulated under alternate stimulation of ultraviolet
and green lights. Distinctive to previous designs, the regulation of
diffraction efficiency fundamentally stems from the modulation of geometric
phase together with dynamical phase retardation, and any intermediate
diffractive state is memorized. Such multi-stability facilitates applications
including energy-saving all-optical signal processing in classical and quantum
level, and phase hologram for anti-counterfeit.
