<p> Compositionally asymmetric multiple quantum well (AMQW) lasers are used for the demonstration of the gain flattening coating functionality. The gain spectra of the lasers are extracted using a non-linear least square fitting method. An optimum facet reflectance spectrum is calculated for a chosen current. For manufacturability, a modified reflectance spectrum of the gain flattening coating is proposed, in order to achieve operation over a wider spectral range without the 'difficult' gap which was a region where lasing was difficult or impossible to achieve due to insufficient gains at these wavelengths. </p> <p> Silicon oxides films with high, medium, and low refractive indices fabricated in an inductively coupled plasma (ICP) enhanced chemical vapor deposition (CVD) system are chosen as the building blocks of the gain flattening coating. An 18-layer coating is designed by the insertion of needle-like refractive index variation with a few optimization methods applied to minimize the merit function. A laser bar holder is custom designed and fabricated. Experiments and modification on the laser bar holder are carried out for better performance. The 18-layer gain flattening coating is then fabricated in the ICPCVD system with an in-situ spectroscopic ellipsometric measurement. It is observed that the non-lasing gap has disappeared after the coating is applied. Without external feedback, the coated laser shows tuning over 85 nm with the central wavelength of 1593 nm, while the uncoated laser has a non-lasing gap of about 25 nm in the central region of the tuning range of 70 nm. </p> <p> Finally, the coherence length of a low coherent source synthesized from the gain flattening coated AMQW laser is measured by using Michelson interferometer. The highest depth resolution that can be achieved is measured as 40 μm. The power intensity of the synthesized low coherence light source from the gain flattening coated AMQW laser is rendered from the interferogram using fast Fourier transform (FFT). </p> / Thesis / Doctor of Philosophy (PhD)

<p>A detailed analysis of coupled cavity semiconductor lasers with asymmetric multiple quantum well (AMQW) active regions is presented in this thesis. The analysis involved design, fabrication, characterization, and simulation of these devices. Although the coupled cavity devices can be multi sectioned, the devices discussed in this thesis are two sectioned.</p><p> A below threshold model for an AMQW coupled cavity device is developed. Non-linear fits of the below threshold spectral data to that obtained from the model were used to extract optimized device parameters. These fits helped to create an understanding of the operation of the devices and paved the way for improved device performance. Optimized device parameters obtained from the below threshold model were later used as input parameters in the development of an above threshold model. This model verified the wavelength selection mechanism employed by coupled cavity diode lasers and predicted the longitudinal modes for sets of injection currents.</p><p> Optical coherence tomography (OCT) is an application where much interest has recently been drawn. The coupled cavity devices fabricated in this work applied with proper modulation of the injection currents and followed by subsequent time averaging have demonstrated short coherence length (-15 μm) and can be an excellent source for synthesized OCT. Rapid wavelength switching (-70 ns, the measurement was limited by detector response time) over the whole range has also been experimentally shown. Because of the high speed (relative to mechanical) wavelength switching ability, AMQW coupled cavity devices have the potential for applications requiring real time measurements including real time synthesized OCT.</p> / Thesis / Doctor of Philosophy (PhD)