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Coupling from single mode fiber to III-V semiconductor waveguide via intermediate polymer waveguide
Dissertation   Open access

Coupling from single mode fiber to III-V semiconductor waveguide via intermediate polymer waveguide

Ben-Hur Viana Borges
Doctor of Philosophy (Ph.D.), Drexel University
Apr 1997
DOI:
https://doi.org/10.17918/00000486
pdf
Borges_Ben-Hur_19975.35 MBDownloadView
PDFOpen Access (License Unspecified),  Open Access

Abstract

A novel approach for the coupling from a single mode fiber to a semiconductor waveguide is proposed in this thesis. The approach consists in utilizing a polymer waveguide with dimensions and refractive indices closely matching a single mode fiber. The objective is to reduce two major loss mechanisms that affect the coupling process, (1) Fresnel reflections, due to the index mismatch at the fiber and semiconductor interface, and (2) field mismatch, due to the geometrical contrast between fiber (cylindrical) and semiconductor (rectangular). The structure was analyzed theoretically by means of two distinct modeling techniques, namely, Alternating Direction Implicit (ADI) method, and coupled mode formulation. The first is a fully numerical approach that solves the Helmholtz wave equation in three-dimensions. This finite difference based technique provides a good insight with respect to field propagation and field confinement even for structures with lateral confinement (rib). The ADI technique, on the other hand, is not able to handle losses as required for a more realistic investigation of this problem. The second is a new analytical approach formulated in terms of the Lorentz reciprocity theorem and is valid for media with either gain or loss. This approach is exact since it utilizes the orthogonal modes of the compound structure. Three important loss mechanisms are also taken into account in this analysis, namely, the leakage of power towards the semiconductor substrate, the power lost to radiation modes (mode mismatching), and the grating radiation loss. Two different excitation conditions are investigated, (1) a single mode fiber butt coupled to the polymer waveguide, and (2) a semiconductor laser monolithically integrated with the semiconductor waveguide. In both cases the wavelength used is 1.3[mu]m. A sensitivity analysis is then performed on all parameters of the structure in the attempt to find an optimized configuration. The results obtained with the orthogonal coupled mode formulation predicted a maximum coupling efficiency of 11% for the first case, and 19% for the second.

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