Design, theory, and applications of broad gain profile indium gallium arsenide phosphide diode lasers

A broadly tunable diode laser system has been developed by employing custom designed asymmetric multiple-quantum-well (AMQW) InGaAsP/InP lasers in an external cavity configuration. Feedback was provided by a diffractive optical element (DOE) with high coupling efficiency and wavelength selectivity, allowing for single mode tuning of the output wavelength by varying the external cavity length. A theoretical description of the external cavity tuning mechanism and the design of custom diffractive optical elements is presented. The tunable laser system has been experimentally used to demonstrate applications in broadband absorption spectroscopy on weak CO2 lines over an 80 nm wavelength region in the NIR. A multi-band k · p model was developed to solve for the sub-band dispersion and envelope wavefunctions of AMQW structures using the Galerkin method. The model is found to treat accurately the multi-band mixing effects and inter-QW coupling between sub-band states in AMQW structures. The model was used to solve for the laser gain spectrum with the simulated device spectra showing good agreement with the experimentally measured properties from several AMQW lasers. By altering the material composition of each QW, it was found that broad tuning ranges can be achieved, under certain operating conditions, using AMQW lasers. An experimental tuning range of 172 nm, using the DOE external cavity, was demonstrated. The design of a flexure mount is presented that employs a magnetic voice coil actuator to provide smooth and accurate tuning of the lasing wavelength of AMQW lasers using the DOE-laser external cavity system. The broadly tunable flexure mount laser system is shown to provide stable, single mode operation and was used to demonstrate an interferometer-based absolute distance measurement system.