Document Details

Document Type : Thesis 
Document Title :
Theoretical Studies on Nonlinear Gain and Noise of Quaternary III-V Semiconductor Lasers
دراسات نظرية عن الكسب غير الخطي والضجيج لليزرات أشباه الموصلات ذات المركبات الرباعية
 
Subject : Faculty of Science 
Document Language : Arabic 
Abstract : Quaternary semiconductor lasers have received much attention because of their potential for use in fiber communication systems. The operation and dynamic characteristics of these lasers are controlled by optical gain and are affected by noise. Calculations of gain and noise by tuning the bandgap energy are perquisite for studying performance of these lasers. Both gain and noise are nonlinear properties, and their calculations are awesome implying tedious theoretical approaches to the interaction of the electromagnetic field with the active material. This thesis presents theoretical modeling of both nonlinear gain and noise of quaternary semiconductor lasers, aiming at developing empirical equations that help in calculation of gain and noise properties as functions of the bandgap energy using simple calculations. First, small signal modeling was introduced to both the frequency noise (FN) and the relative intensity noise (RIN) and also to the associated linewidth and their dependence on the gain formulation. Three common formulas of nonlinear gain were used. Influence of gain suppression on the frequency characteristics of the RIN and FN spectra as well as on the damping rate and frequency of relaxation oscillations were elucidated. Variations were seen in the levels of RIN and FN in the regime of the relaxation frequency with changing the form of optical gain because of variation in the damping rate and relaxation frequency. The tolerances in predicting both the RIN and FN levels due to these gain forms were 1% and 14%, respectively, which corresponded to tolerance of the linewidth of 21.6% at low frequency of 10 MHz, while they were 39% and 21.6% at the relaxation frequency. In the second part, modeling of the linear and nonlinear gain was introduced basing on a modified third perturbation approach that takes account of electronic transitions between the conduction band and both the heavy and light hole bands of the active layer. The proposed model was applied to In1-xGaxAsyP1-y/InP and In1-x-yGaxAlyAs/InP lasers. The results show that the linear gain and nonlinear gain coefficients decrease with the increase of the bandgap energy for both lasers. The In1-xGaxAsyP1-y/InP laser was found to exhibit higher linear and nonlinear gain coefficients and lower transparent carrier density than those of the In1-x-yGaxAlyAs/InP. The obtained results on gain characteristics of the complicated approach of gain were used to develop simplified empirical equations that function in the bandgap energy of the quaternary alloy. These simplified relationships were then used in the rate equation model that describe the laser dynamics to simulate the spectral properties of relative intensity noise (RIN) as a function of the bandgap energy over the relevant ranges. The RIN levels were shown to increase with the increase of the bandgap energy around the relaxation frequency of the laser which shifts to lower frequencies. The level of the low frequency RIN is almost same in both lasers, while the high frequency RIN in the In1-x-yGaxAlyAs/InP is one order of magnitude lower. In addition to the fitting equations of gain characteristics in terms of the bandgap energy, the simulated noise spectra were used to introduce fitting equations to the RIN levels around the relaxation frequency and in the regime of low frequencies. The obtained result of this study enables calculations of the complicated spectral characteristics of linear and nonlinear gain and noise via simple calculations. Therefore, this thesis adds to the theory of the semiconductor laser and helps to simplify its application to simulate performance of related application systems. 
Supervisor : Prof. Dr. Moustafa Farghal Ahmed 
Thesis Type : Doctorate Thesis 
Publishing Year : 1444 AH
2023 AD 
Added Date : Wednesday, August 16, 2023 

Researchers

Researcher Name (Arabic)Researcher Name (English)Researcher TypeDr GradeEmail
ريم عائض العتيبيAlotaibi, Reem AyedhResearcherDoctorate 

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