Abbe diffraction limit has always been an important subject in conventional far-field focusing and high resolution imaging systems. The width of a focal spot is usually limited to 0.5λ∕NA because of the diffraction effect, which limits the resolution of optical microscopy and nano-lithography a lot. Recently, Recently, the studies of the optical superoscillation lens (SOL) enable us to break the limitation in both theory and practice successfully by modulating the amplitude and phase of incident light periodically. However, a lot of parameters need to be figured out to design a suitable SOL, which was a troublesome process and needed a great amount of calculation. Hence it is difficult to obtain the optimal SOL design.

Here we developed a genetic algorithm (GA) to design phase-type super-oscillation lens (SOL) for subdiffraction focusing in the optical far-field. The simulation result was exciting (0.105λ/NA, near 0.01λ2 when NA approaching 1). Experimentally, the phase control was dynamically achieved by a feedback-based wavefront shaping method using a spatial light modulator. The minification was 65.5% in the experimental demonstration, which meant the width of the focal spot could be only dozens of nanometers. Thereofore, this technique provides a possible way to make progress in the nanotechnology such as microscopy and optical lithograohy.

This research was published in "Zhengdong Gao, Yanqi Qiao, Lanting Li, and Xianfeng Chen, Far-field super-focusing by a feedback-based wavefront shaping method, Optics Letters, 44(4), 1035-1038 (2019)".