100 Gbps ptical coherent modem for low earth orbit optical inter-satellite links

Abstract

Free space optical communication (FSOC) provides a viable and cost-effective solution for future satellite systems with advantages in bandwidth, unregulated frequencies, and reduced system mass, volume, and power consumption in comparison with radio frequency systems. Several FSOC systems successfully demonstrated links between spacecraft and Earth ground stations as well as inter-satellite links. Commercial industry, including companies such as SpaceX and Telesat, have taken an interest in utilizing the benefits of FSOC for proposed LEO constellations and using optical inter-satellite links (OISLs) to reduce the need for expensive worldwide ground tracking networks. State-of-the-art FSOC space terminal data rate performance is 5.625 Gbps using coherent BPSK detection, achieved by the Tesat and DLR laser communication terminal (LCT) in 2008. The Tesat and DLR LCT demonstrated LEO to LEO OSLs over a link distance of 5100 km.

Within the past decade, the terrestrial communications industry advances in optical coherent DSP ASICs and integrated fiber optic component packages have enabled high capacity optical coherent communications systems with data rates of 100 Gbps and greater. It is desirable to leverage the data rate performance and cost point of these technologies to develop a state-ofthe- art optical coherent modem system for FSOC space applications. The goal of this work is to develop an optical coherent communications modem for LEO-to-LEO inter-satellite links with improvement in data rate of 10 times the current state of the art of 5.6 Gbps using commercial off the shelf components, such as optical coherent DSP ASICs, coherent transmitters, coherent receivers, and lasers, with minimal modifications as needed for space use.

This work focuses on developing an optical coherent communications modem for data rates up to 100 Gbps using commercial telecommunications industry components compatible with lOOG wavelength division multiplexed (WDM) coherent systems. We develop a process for selecting commercial optical coherent technologies that can meet performance requirements in a LEO space environment. We develop optical coherent modem hardware and assess the selected commercial optical coherent technologies for uses in the space environment. We identify and develop cost-effective modifications based on radiation characterization, ensuring that we can achieve successful space operation and meet performance requirements.