20-GHz bandwidth optical activation function based on a semiconductor laser

TL;DR

This paper demonstrates a broadband optical activation function using a semiconductor laser with a 20 GHz bandwidth, enabling nonlinear processing in optical neural networks directly in the optical domain.

Contribution

The authors introduce an optical activation function based on a semiconductor laser operated in an unstable regime, achieving high-speed nonlinear activation in the optical domain.

Findings

Achieves 20 GHz operation bandwidth.

Mimics ReLU for <5 GHz, ELU for >5 GHz.

Operates in the unstable-locked regime of a semiconductor laser.

Abstract

Optical neural networks usually execute the linear multiply-accumulate operation in the optical domain, whereas the nonlinear activation function is mostly implemented in the digital or electrical domain. Here we demonstrate a broadband activation function operated in the optical domain. The optical activation function (OAF) is achieved by a semiconductor laser with optical injection, which is operated in the unstable-locked regime above the Hopf bifurcation. The operation bandwidth of the OAF reaches as high as 20 GHz, which is limited by the relaxation oscillation resonance frequency of the semiconductor laser. The OAF mimics a ReLU function for modulation frequencies below 5 GHz, while resembling an ELU function for frequencies above 5 GHz.