Linearization of Directly Modulated Lasers for Enhanced Optical Wireless Communication

The demand for high-speed optical wireless communication (OWC) has surged due to the growing number of high bandwidth applications. Directly modulated lasers (DMLs) are a necessary alternative to light-emitting diodes (LEDs) for achieving higher speeds. However, at high data rates, the intrinsic non-linearity of DMLs degrades signal quality, limiting achievable data rates. We demonstrate the application of the ABCD linearization technique to a 2.5 GHz blue laser employing non-return-to-zero (NRZ) and carrierless amplitude/ phase (CAP) modulation. Using a 3.5 GHz PIN photodetector and feed-forward equalizer (FFE), this method improves the achievable data rate by ~1.8 times for NRZ, from 3.8 Gb/s to 7 Gb/s, and by 2.3× for CAP-16, achieving 9 Gb/s. These results validate the ABCD approximation method as a simple yet effective solution for mitigating laser non-linearity and enhancing data rates in high-speed OWC systems.