Paper 14090-1
Paper 14090-1
Passive and Self-Mode locking in two section InGaAsP/InP Quantum Well Laser in an External Cavity
12 April 2026 • 14:00 - 14:20 CEST | Leicester/Salon 12 (Niveau/Level 1)
Abstract
Mode-locked laser diodes (MLLDs) are at the heart of ultrafast laser science, generating laser pulses that can be harnessed for emerging technologies. In this study, we explore a two-section InGaAsP/InP quantum well laser (840 μm length, λc = 1570 nm, 50 GHz internal roundtrip frequency) with a single-side antireflection coating in a tunable 15 cm external cavity with a 1 GHz repetition rate. Compared to our previous monolithic operation, clean passive mode-locking was achieved, yielding pulse durations below 1.37 ps at 100 mA gain current and −0.8 V absorber bias under a 20 m SMF-28 dispersion-compensating scheme. We demonstrate that self-mode locking in this external cavity configuration is also possible and significantly enhanced when the combined system cavity lengths are chosen in specific ratios and a flexible external cavity allows for precise tuning for sub-picosecond pulse formation. These findings point to the potential utility of the system in ultrafast terahertz spectroscopy with variable repetition frequency.
Presenter
Joshua N. Onkangi
Ruhr-Univ. Bochum (Germany)
Mr. Joshua Onkangi is a doctoral researcher at the Photonics and Terahertz Technology Chair, Ruhr University Bochum. His research focuses on advanced photonics and laser physics, particularly the characterization of mode-locked and external cavity semiconductor lasers for ultrafast applications. He investigates coherent pulse formation, dispersion management, and coupled-cavity dynamics in quantum well lasers, aiming toward efficient terahertz radiation generation and detection. Joshua earned his master’s degree in nuclear science from the University of Nairobi, where he applied machine learning to laser-induced breakdown spectroscopy, and a bachelor’s degree in physics from Egerton University. He is an active SPIE member, with publications in laser spectroscopy and nuclear forensic analysis, and has presented his work at several conferences (LIBS, EMSLIBS). His current research seeks stable, flexible mode-locking schemes for tunable ultrafast terahertz spectroscopy.