Photonic Analog-to-Digital Converter

Analog-to-digital conversion (ADC) is an essential operation in many applications including radar, sensing, communications, and instrumentation. Two key parameters of an ADC are its sampling rate and resolution, measured in samples per second and number of bits, respectively. Unfortunately, as the sampling rate increases the maximum resolution is reduced. High-speed electronic ADCs (>10 GS/s) are currently limited to about 4-6 effective bits of resolution, while moderate speed ADCs ( 8 bits of resolution. Obtaining high resolution at high speeds could allow for many advances in communication systems. For example, software-defined radios could have a fully digital receiver which digitizes the carrier frequency directly rather than forcing a down-conversion operation. A fully digital radio is a key goal in the community, but is not practical at commonly used high carrier frequencies (>1 GHz). Maintaining high resolutions at high sampling rates will enable efficient bandwidth utilization and the compensation of various distortions such as those arising from multiple reflections at much higher carrier frequencies that are used in the super high frequency (SHF) band employed in various satellite communication systems. Additionally, great interest has recently been given to using fast ADCs in high speed optical communication systems. These ADCs are used to compensate for various distortions such as dispersion and usually only have a few bits of resolution. However, as data rates increase and more complex optical signaling become available (coherent systems), higher sampling rates and higher resolutions will be required. More bandwidth-efficient optical M-ary systems (as opposed to binary systems) can also be developed. In addition to communications, there are also applications in advanced instrumentation and radar systems. As a diagnostic and signal analysis tool, high speed and high resolution ADCs which bridge the gap between the analog and digital worlds are indispensable.