|M.Sc Student||Michael Yasin|
|Subject||High Power Integrated Laser Amplifier|
|Department||Department of Physics||Supervisor||Professor Fekete Dan|
In this work weak optical confinement structures with broad and narrow waveguides were utilized to optimize the diode lasers for high power operation. The consequent larger size of the fundamental mode results in reduced optical power density, which is critical for preventing of catastrophic optical damage and spatial hole burning.
However, the enlarged waveguide thickness increases the overflow current, which does not contribute to lasing and increases the temperature of the active region that decreases quantum efficiency and results in the higher nonradiative recombination.
In addition, the price paid for the broadened fundamental mode is the decreased optical confinement factor. The concomitant decrease in modal gain results in the increase of the threshold current density in the short cavity lasers. At least partially, high quality resonator, low internal cavity losses and multi quantum well design of the lasers compensated it.
Using of AlGaAs cladding and waveguide layers in these structures is important for reducing of the electron leakage from the active region as well as for the optical confinement.
d-doping plays significant role in increasing of the characteristic temperature and in the optimization of the transparency current density to minimize the threshold current density of the QW lasers. It was shown in the work, that due to the d-doping control on the transparency current density, it can be used as one of the “independent” parameters for optimization of the laser diode performance.
Asymmetric structure design together with appropriate doping of waveguide and cladding layers allowed the predominance of the fundamental lasing mode over the higher order modes.
The new waveguide design with a large transverse spot size resulted in low internal losses and extremely narrow for AlInGaAs structures vertical far field beam divergence. Long cavity lasers, which are necessary for high power operation, can significantly benefit from the low loss and high efficiency offered by the new structures.
Excellent performance of these laser diode structures make them very well suited for applications as single emitters, as well as for the more complicated high brightness devices such as laser bars and monolithically integrated laser-amplifier devices.