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Broad band optical transmission measurements in semiconductor waveguides

University of British Columbia

A broad band optical transmission measurement system has been realized to determine properties of light propagation in semiconductor waveguides in the 800-1200 nm wavelength range. Illumination from a halogen source is coupled to a single-mode optical fibre and focused onto the input facet of the waveguide via a confocal, diffraction limited lens system. The output light is imaged by another diffraction limited lens through a spatial filter and coupled into a high resolution Fourier Transform Interferometer. The samples studied were epitaxially grown, strained InGaAs quantum well waveguide structures. Measurements of the transmitted spectra over a -1600 cm-1 spectral range in the vicinity of the fundamental absorption edges of these samples resulted in the determination of the guided mode's group index of refraction (and its dispersion), and the absolute absorption coefficient for both transverse electric (TE) and transverse magentic (TM) polarizations. The measured group indices were compared to those calculated by solving Maxwell's equations using a simple quasi-two dimensional model for the InGaAs quantum well's index of refraction. Agreement with the TE group index data was good, but the large difference in the TE and TM dispersion near the bandgap energy clearly demonstrates the anisotropic nature of the quantum well's index of refraction. The TM absorption edge was well above the InGaAs bandgap and its detailed shape was successfully compared with a calculation based on a bandstructure obtained using k-p theory. The TE absorption was measured below the InGaAs bandgap and it's exponential energy dependence was tentatively interpreted in terms of a bulk model for the Urbach

Thesis/Dissertation

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2009-01-27

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http://hdl.handle.net/2429/3919

Engineering Physics

University of British Columbia

UBCV

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