An investigation of noise properties in actively modelocked semiconductor diode lasers for application in next-generation optoelectronic analog-to-digital converters

There are several interesting applications for well-behaved optical bit streams in addition to high-speed telecommunications. One such possibility is in forming the backbone of a high-speed analog-to-digital converter (ADC) system. Because the digital accuracy (bit resolution) of traditional electronic ADCs begins to be severely limited by transistor bandwidth once the sampling frequency exceeds a few GHz, there have been several recent efforts to overcome these limitations through the use of high-bandwidth optical sampling systems.; This research focuses on achieving the ultralow-noise pulsetrains needed to perform high-accuracy analog signal sampling with an actively-modelocked semiconductor diode laser. Innovative techniques have been used to measure the ultralow carrier noise at bit rates as high as 10 GHz, and the properties of supermode noise in harmonically-modelocked ring laser geometries has been measured out to Nyquist offset frequencies for the first time. Finally, optical and electronic methods have been developed to reduce the amount of laser noise, resulting in the lowest noise measured to date for an external-cavity actively-modelocked semiconductor diode system.