Fiber-optic, LEO-based, communications ring

Abstract

This paper continues the development of a concept for a low-earth-orbit-based optic-fiber-communication system that may ameliorate some limitations of present space communications systems. Starting with an assumption that a circum-terra ring can be deployed in LEO, a high-bandwidth, optical-fiber-based, communication system has been proposed as the first of a system of LEO and higher-orbit (MEO) rings for different purposes. These rings about the Earth would complement existing terrestrial and space communications networks and thereby improve global connectivity and throughput. In particular, networking issues necessary for both initial and expanded-ring system communications are addressed. A proposed component of a system of circum-Terra rings, the LEO ARCHIPELAGO, would consist of about 200 sub satellites in a single orbital plane interconnected using a 40,000 km fiber-optic ring. Traditionally, both Inter-Satellite Links (ISL) and Inter-Ring Links (IRL) links have relied on RF communication links. However, with the prospect of the LEO ARCHIPELAGO� using high tensile-strength fiber cables for ring stabilization, the use of fiber-optic-based ISL becomes a possibility. A low-loss hybrid architecture for a Reconfigurable Optical Add Drop Multiplexer (ROADM) would be the major part of each LEO satellite node that provides for bi-directional links over a ring fiber. This architecture for ROADM subsystem is one of its kind. It performs better than the latest available ROADM models and would reduce the overall network operating cost. The hybrid ROADM architecture combines the best features of Planar Light-wave Circuit (PLC) and Wavelength Selective Switch (WSS) technology. Signals coming out of the hybrid ROADM node need not be amplified for a significant distance, thereby adding to the cost-reduction factor. Higher throughput data along with the facility to assign any wavelength (color) to any port at the add/drop site, completely by software control and unattended operation are a few of the advantages of using 'colorless' ROADM architecture. Copyright �2010 by the International Astronautical Federation. All rights reserved.