Bragg Gratings in Semiconductor WaveguidesMaster's Thesis from the year 2001 in the subject Electrotechnology, grade: with distinction, City University London, 50 entries in the bibliography, language: English, abstract: Bragg gratings are important devices for both optical communications and sensing. These devices are used to design very narrow band optical filters, which can be used in wavelength division multiplexing (WDM). It is also perceived that Bragg gratings will be used to compensate the dispersion in modern fibre optic telecommunication networks. Semiconductor gratings are usually integrated into lasers to control the operating wavelength. City University Photonic Modelling Group is a world leading research group on the use of rigorous numerical techniques to design and optimise advanced photonic devices for optical communications. The research group has already achieved results on hypothetical one-dimensional (1-D) and realistic two-dimensional (2-D) structures. In this project a combination of three numerical methods has been used, all of which are rigorous, to simulate realistic three-dimensional (3-D) structures in semiconductor waveguides. The combination of these three accurate methods, the finite element method (FEM), the least squares boundary residual (LSBR) method and the transfer matrix method (TMM) turned out to be superior to the widely used coupled mode theory (CMT). The numerical study of different Bragg gratings shows interesting dependencies of the characteristics of the gratings on the different design parameters. The work was carried out for different mesh distributions, different numbers of mesh divisions and different computational parameters. Another focus of the work was on the stability of the transmission and reflection coefficients obtained from the LSBR program. Furthermore the effect of inaccuracy occurring during the fabrication process has been studied. The results of this work have been compared to results found by other groups and fellows. We can say that this proj |
Contents
| 5 | |
DIFFERENT TYPES OF BRAGG GRATINGS | 21 |
SIMULATION METHODS | 28 |
SIMULATION RESULTS | 41 |
CONCLUSION | 92 |
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Common terms and phrases
100 periods accurate allow amplitude apodisation profiles apodised gratings applications approach band bandwidth boundary Bragg gratings calculated centre changed chapter characterised chirped gratings compared compensate components computed condition considered coupling decreased devices discontinuity junction discussed dispersion effect electric element equations Erbium error Fig fabrication fibre field filter Gaussian apodised given grating length grating periods height higher impedance approach important increased Introduction lasers layer light linearly loss low side lower LSBR materials maximum mesh mesh division method modes multiple gratings needed normal number of periods occurs optical fibre parameters phase-shifted grating possible problems propagation constant pulse reflection coefficient Reflection spectrum refractive index results obtained semiconductor gratings shown in Fig side simulation single spectra structure Table technique theory transfer matrix transition transmission coefficient types uniform gratings Variation varying waveguide wavelength waves widely
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Page 18 - According to the law of reflection, the angle of incidence equals the angle of reflection, and the incident ray, the reflected ray as well as the normal ray always lie in the same plane.
Page 18 - The first condition for total internal reflection is that the refractive index of the cladding is lower than that of the core.
Page 18 - The refractive index is defined as the ratio of the speed of light in vacuum to the speed of light in the medium.
Page 5 - Finally, I would like to express my deepest gratitude to my parents for their encouragement and support throughout my studies.
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