  Despite over 40 years' development of optical logic computing, the studies
have been still struggling to support more than four operands, since the high
parallelism of light has not been fully leveraged blocked by the optical
nonlinearity and redundant input modulation in existing methods. Here, we
propose a scalable multi-input optical programmable logic array (PLA) with
minimal logical input, enabled by parallel spectrum modulation. By making full
use of the wavelength resource, an eight-input PLA is experimentally
demonstrated, and there are 2^256 possible combinations of generated logic
gates. Various complex logic fuctions, such as 8-256 decoder, 4-bit comparator,
adder and multiplier are experimentally demonstrated via leveraging the PLA.
The scale of PLA can be further extended by fully using the dimensions of
wavelength and space. As an example, a nine-input PLA is implemented to realize
the two-dimensional optical cellular automaton for the first time and perform
Conway's Game of Life to simulate the evolutionary process of cells. Our work
significantly alleviates the challenge of extensibility of optical logic
devices, opening up new avenues for future large-scale, high-speed and
energy-efficient optical digital computing.
