Modeling of DFB surface emitting lasers and semiconductor laser arrays
Lee, Shing Man
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https://hdl.handle.net/2142/21015
Description
Title
Modeling of DFB surface emitting lasers and semiconductor laser arrays
Author(s)
Lee, Shing Man
Issue Date
1991
Doctoral Committee Chair(s)
Chuang, Shun-Lien
Department of Study
Engineering, Electronics and Electrical
Physics, Condensed Matter
Physics, Optics
Discipline
Engineering, Electronics and Electrical
Physics, Condensed Matter
Physics, Optics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Physics, Condensed Matter
Physics, Optics
Language
eng
Abstract
Theoretical modeling of novel semiconductor laser systems, i.e., distributed-feedback (DFB) surface emitting lasers and semiconductor laser arrays, is presented. The DFB surface emitting lasers can produce stable single-mode outputs even under high bit-rate direct modulation and form two-dimensional laser arrays. A simple and accurate analytical model using the coupled-mode theory is developed to describe these surface emitting lasers. Due to the simplicity of the model, the desired laser output characteristics, i.e., low threshold condition, large side mode suppression ratio, and stable and low noise Bragg-mode outputs, can be obtained by systematically optimizing the device length, optical coupling and phase shifter in the device.
The nonplanar laser arrays are of much interest because of their simple fabricating procedures and very high output power. A theoretical study is performed to understand the efficiency and far-field and near-field patterns. A number of important physical mechanisms for high power semiconductor laser operations are studied using a self-consistent model. These include the two-dimensional current spreading in the cladding layers, the coupling between the carrier distribution and the photon distribution, and the carrier saturation effects at high power operation. The mesas, bends, and grooves are treated as adjacent waveguides, each described by the effective index method. The output field patterns in the nonplanar laser structures are composed of a linear combination of the individual waveguide modes. The multimode operation in practical devices can be explained by spatial hole burning effects, nonuniform current injection, and competition for available carriers in the neighboring waveguides between different optical modes. The possibility of obtaining phase-locked output by reducing the groove depth is also investigated. A finite-difference time-domain (FDTD) model is used to study the radiation losses due to the bend. A groove depth as small as 0.1 $\mu$m can be used for maximum optical coupling while the bending loss is still large enough to suppress the lateral lasing operation in the nonplanar laser array.
The highest semiconductor laser output powers have been achieved by the laser arrays employing optical turning mirrors. The effects of the rough turning mirrors on the laser array performance are estimated using the FDTD method. A number of steps are employed to reduce the computation time on these very large mirrors (about sixty wavelengths) to make the FDTD model a possible computer-aided design tool. The computation time is reduced by a factor of twenty.
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