Fig. 2: Classification criteria for the FSO encoders.

a Optical/digital configuration categories based on contributions of the digital backend. The digital backend can perform either simple or complex operations, or even no operation at all. b Imaging configuration categories based on adaptability to the conventional imaging system. The FSO encoder can be added to the conventional system or replace one of the optical components. Multiple layers of encoders can be used to build an entire optical system. c Design frameworks, including fundamental physical laws, digital operation being implemented in optics, and computer-optics co-optimization.