Numerical Modelling, Simulations and Experimental Analysis of Quantum Well, Quantum Dot and Quantum Dash Mode-Locked Lasers

Abstract

Mode-locked lasers are essential light sources for generating ultrashort pulses, widely used in high-speed optical communication systems such as Time-division multiplexing and Dense Wavelength Division Multiplexing (DWDM). These lasers are preferred over other light sources for their broad bandwidth, high-peak power and highly coherent light pulses. This work investigates the mode-locking phenomenon in various quantum-sized structures, including multi-quantum wells, quantum dot and quantum dash-based lasers. The primary objective of conducting this research is to gain a deeper understanding of the complex dynamics occurring within the laser cavity. The study employs various numerical modelling, simulations, and experimental analyses to achieve the objective.

Numerical modelling is based on two key approaches: the Time Delay Oscillator (TDO) model and the Delay Differential Equation (DDE) model. Both models use the time-domain lumped element approach to understand the physical processes within the laser cavity. Specifically, the DDE model is developed using the Time Domain Travelling Wave (TDTW) approach to analyze the passive mode-locking phenomenon in lasers. Both models were implemented in the Simulink platform.

The simulation section focuses on the quantum well laser designs due to the current limitation of the Photon Design Tools, Harold and PICWave to support only quantum well-based structures. The parameter values for the quantum well-based simulations from PICWave were extracted to be used in Simulink as PICWave uses a TDTW engine, thus providing a basis for the parameter extraction.

The experimental analysis focuses on quantum dash lasers, examining various aspects of the laser device parameters such as the repetition rate, pulse width, and threshold currents. Additionally, the study investigates the impact of factors such as temperature and injection currents on key parameters like L-I curves, optical spectra, dispersion, and mode-locking behaviour of the laser device.