Stable, Tunable High-Repetition-Rate Operation of Gain-Switched Semiconductor Laser via Hybrid Current-Pulse-Width Control

The phenomenon of pulse tailing, primarily caused by relaxation oscillations, presents a significant challenge to increasing the repetition rates of gain-switched semiconductor lasers. This paper proposes a novel approach to mitigate this issue by simultaneously regulating both the magnitude and pulse width of the pump current, enabling stable, tail-free pulse generation across a broad range of repetition frequencies. Numerical solutions to the carrier rate equations are first employed to investigate the origins of optical pulse tailing. By reducing the current injection duration from 200 ps to 50 ps, carrier injection is effectively truncated, suppressing relaxation oscillations. However, this reduction also leads to a decrease in peak optical pulse power, limiting the laser’s applicability. Increasing the injection current’s magnitude provides a solution. Consequently, a high-precision circuit design has been developed to digitally adjust both the magnitude with a precision of ~3 μA and the pulse width with a resolution of 5 ps. This configuration successfully generates 200 ps optical pulses with a single-pulse energy of 0.96 pJ at 1550 nm, over a repetition rate range from 10 kHz to 1 GHz. With this laser as the transmitter, RZ-OOK modulated signal transmission at a slot rate of 250 MHz has been realized. The proposed scheme offers a stable, reliable optical emission source, making it ideal for high-speed, high-capacity optical time-division multiplexing communication, time-resolved spectroscopy, and laser ranging and imaging applications.