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Characterization of loss/gain in optical waveguides

Themistos, C. (1998). Characterization of loss/gain in optical waveguides. (Unpublished Doctoral thesis, City, University of London)


The recent advances in lightwave technology have revealed the need for the accurate modelling of a range of optoelectronic devices, via efficient computer algorithms. The characterization of optical waveguides, which are the key elements in integrated optics design, requires the accurate determination of the impact of various material parameters and fabrication tolerances, for example. During the early years of the development of the field, the estimation of loss and gain was not considered critical, since it was maintained at low levels, due to the simplicity of the structures and the properties of the materials. The loss and gain analysis is becoming of considerably greater importance nowadays, with the introduction of new laser technology and integrated optics design which has enabled the fabrication of complicated structures, where various metallic elements and active regions are combined in a large scale integration.

The finite element method, which is a very popular numerical approach for the solution of many engineering problems, is currently recognized as a very powerful tool for the analysis of several optical waveguide structures, particularly structures with arbitrary shapes, index profiles, nonlinearities and anisotropies. Most of the formulations used in the finite element method are restricted to structures without modal loss or gain. The Ht vector formulation, defined in terms of the transverse magnetic field components, which was recently introduced for such analysis though it is considered accurate, may result in an increase of the computing time, due to the involvement of complex matrices and the limitation of efficient solvers. Therefore, more efficient algorithms are required, especially in the cases where the optical waveguides suffer small loss or gain, which is common in most of the practical applications considered.

In this work, a finite element analysis employing the H-field formulation, with the aid of the perturbation technique, has been developed to calculate the modal loss or gain for several different types of optical waveguides. Further, a semi-analytical approach has also been developed and used to obtain the complex propagation constant of simple optical waveguides from the solution of the complex transcendental equation and the use of the effective index approach. The accuracy limit of the perturbation technique, which is limited to structures with low to medium loss or gain is also examined. An approximate approach for the calculation of the modal loss or gain, in terms of the mode confinement factor has also been employed for certain types of optical waveguides.

The above approaches are used for the solution of several planar optical waveguides and optical waveguides with two-dimensional mode confinement. The results obtained were compared with previous results for some of the structures examined, and found to be in good agreement. Finally, the finite element approach with the introduction of a perturbation technique has been used for the characterization and optimization of certain types of optical waveguides of practical interest, such as optical polarizers, electro-optic directional coupler modulators and metal clad fibers used in near-field scanning optical microscopy, which enhance surface-plasmon properties.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TJ Mechanical engineering and machinery
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments: School of Science & Technology > Engineering > Electrical & Electronic Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
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