Study of Outputs Power of Broadly Tunable InGaAsp/InP AMQW Lasers

Abstract

<p>Broadly tunable InGaAsP/InP asymmetric multiple quantum well (AMQW) ridge waveguide laser diodes suffer from low output power. The output power problem of the AMQW laser diodes limits the use of these lasers in certain applications. Both theoretical and experimental studies were carried out in this work to understand the reasons behind this output power problem and to put forth solutions to this problem. As a starting point a commercial beam propagation method (BPM) optical simulator was used to optimize the confinement factor of the laser diodes. The laser diode output power almost doubled as a result of optical confinement optimization, which opens the door for improvement from electrical and thermal optimization.</p> <p>A commercially available partial differential equation solver, FlexPDE, was used to solve the main electronic and thermal equations and simulate a laser diode device. The FlexPDE simulations -which were validated with published data-showed poor current injection efficiency to the center of the device active region. The FlexPDE simulations showed that the main reason for this poor current injection efficiency is the ridge structure. Since the ridge structure is an essential part of this type of laser diode, effort was put forth to reduce the effect of the ridge structure on the current injection efficiency. Both simulation and experimental data showed that extending the doping profile closer to the active area would improve significantly the output power. On the other hand, a proposed forced electrical confinement method showed potential to improve the output power of the device theoretically and experimentally. The over all output power improvement went from a range of 2-5 m W to a range of 15-18 m W as a result of this study. A discussion of the two distinct output power profiles is included in the study, while detailed explanations of the dip in the power profile supported by experimental data are reported.</p> <p>A new method of distance measurement using one of the first, optimized, broadly tunable InGaAsP/InP short-external-cavity diode lasers is reported. Non-linear, least squares fitting method was used to extract estimates of distance from the raw data. This fitting method together with the wide tuning range (100 nm) made it possible to achieve sub-micron resolution of distance even in the presence of noise.</p>