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 (>10Gs/s) are currently limited to about 6 effective bits of resolution, while moderate speed ADCs (<500Ms/s) can have 10 or more effective bits of resolution. It is a goal of this STTR to simultaneously achieve both high sampling speeds and high resolution. ADCs which use photonic technology to improve their performance have achieved drastic advances in sampling rate. This is especially true for time-limited signals as sample rates of many hundreds of Gs/s have been recorded, exceeding purely electronic ADCs by 1-2 orders of magnitude. However, this does not translate into high resolution samples, especially for continuous-time signals. In fact, high speed continuous-time photonic-assisted ADCs typically have resolutions of just 3-5 bits even at the more modest 10Gs/s sampling rates. The resolution limitation comes from several sources, including mismatches between components and signal-to-noise ratio (SNR) issues. We have proposed a new method of photonic-assisted ADC which has improved tolerance for component mismatches and a higher SNR. As such it is uniquely poised to address the problems previous optical ADCs have had with achieving high resolutions.