| This thesis presents a study of chirped grating index-coupled 1.55-μm InGaAsP/InP distributed feedback (DFB) lasers whereby the chirping is generated by the use of a curved ridge waveguide over a uniform Bragg grating. The geometry of the curved, or S-bend, waveguide is based on the tilted-sine function. The focus of this study is on the following static characteristics of the lasers: power/voltage/current (P-I and V-I characteristics) and spectral (spectrum, main longitudinal mode wavelength, and sidemode suppression ratio). It is demonstrated, both theoretically, through numerical simulations, and experimentally, that chirped gratings can resolve in a controlled manner the Bragg mode ambiguity normally associated with uniform grating index-coupled symmetrical DFB lasers. Furthermore, by adjusting the total phase shift through the chirping function, the wavelength of the main longitudinal mode can be set within the Bragg stopband bounds. More complex DFB structures such as arrays (4-, 6-, and 8-element) and Y-DFB configurations using curved waveguides were also realized and investigated for use in different applications including wavelength selection by waveguide bending (arrays), multi-wavelength devices with a common output (Y-DFBs), and generation of microwave/millimeter-wave signals by optical heterodyning (Y-DFBs). |
