Since the dawn of digital computing, scientists have dreamed of building artificial neural network that would function like biological brain and solve difficult problems. As nanophotonic circuits became a reality, researchers have tried to create neural networks that would run at the speed of light, but translating a key mathematical component of artificial neurons, the nonlinear activation function, from the electronic to the optical realm proved elusive.
Now, a nine-member team from the Hong Kong University of Science and Technology, Hong Kong, has built an all-optical artificial neural network and applied it to a complex simulation (Optica, doi:10.1364/OPTICA.6.001132). The network incorporates both linear functions, powered by spatial light modulators, and nonlinear activation functions based on the quantum interference effect known as electromagnetically induced transparency (EIT).