Publications

The Integrated LCRD LEO User Modem and Amplifier Terminal (ILLUMA-T) payload was the first space-based user terminal to demonstrate successful two-way optical communications with a ground terminal via NASA's Laser Communications Relay Demonstration (LCRD). In order to acquire the link, the ILLUMA-T optical module open loop points a wide beacon at the LCRD acquisition sensor. The initial pointing of the beacon is based on real-time ISS position and attitude information and precalculated LCRD ephemeris. This paper examines the on-orbit pointing performance of ILLUMA-T during the mission.

Accurate conversion of wideband multi-GHz analog signals into the digital domain has long been a target of analog-to-digital converter (ADC) developers, driven by applications in radar systems, software radio, medical imaging, and communication systems. Aperture jitter has been a major bottleneck on the way towards higher speeds and better accuracy. Photonic ADCs, which perform sampling using ultra-stable optical pulse trains generated by mode-locked lasers, have been investigated for many years as a promising approach to overcome the jitter problem and bring ADC performance to new levels. This work demonstrates that the photonic approach can deliver on its promise by digitizing a 41 GHz signal with 7.0 effective bits using a photonic ADC built from discrete components. This accuracy corresponds to a timing jitter of 15 fs - a 4-5 times improvement over the performance of the best electronic ADCs which exist today. On the way towards an integrated photonic ADC, a silicon photonic chip with core photonic components was fabricated and used to digitize a 10 GHz signal with 3.5 effective bits. In these experiments, two wavelength channels were implemented, providing the overall sampling rate of 2.1 GSa/s. To show that photonic ADCs with larger channel counts are possible, a dual 20- channel silicon filter bank has been demonstrated.