Optical satellite communications

A first step toward developing and deploying free-space optical communication systems is the ability to model and simulate them to enable analysis, testing, and to understand how design affects performance.

For point-to-point free-space optical links, models were developed in an HTSN Challenge program collaboration involving the NRC, Optiwave, the University of Ottawa, MDA Space, McMaster University and Stratotegic. These models, describing communication systems where a laser beam is used to transmit information between 2 points, have been incorporated into Optiwave's commercial software packages. Using an extensive library of components and atmospheric propagation models calibrated against field data, the users of Optiwave's Optisystem can design links to be used either between satellites, between ground sites or between ground and space (high-altitude platforms, satellites, etc.) and obtain realistic performance predictions.

For full-scale satellite systems, the HTSN Challenge program supported the development of a constellation testbed through a collaboration between the NRC, Carleton University and MDA Space. This testbed makes it possible to simulate data traffic and overall system performance in real time while the testbed is running, allowing the user to explore performance as a function of input such as constellation topology, satellite and ground station specifications, data transfer protocols, handover protocols, controller configuration, routing protocols, and so on. The testbed also provides traffic data sets that can be used to train AI models to optimize constellation operations.

Beyond models and simulations, the NRC and our collaborators are working to establish real-life testbeds to validate free-space optical technologies and to acquire operational data and field experience with this cutting-edge technology.

A small observatory named ARTEMIS at the NRC is available to perform ground-to-ground and ground-to-high-altitude platform tests. An HTSN Challenge program collaboration between the NRC, Lux Aerobot, McMaster University, MDA Space and Optiwave is using ARTEMIS to help develop and demonstrate mid-infrared (mid-IR) links that are less affected by weather conditions. In a second HTSN Challenge program collaboration between the NRC, the University of Ottawa, Optiwave, McMaster University, MDA Space and Stratotegic, this testbed is being used to help develop and demonstrate dual-use free-space links, where the laser beam transfers both data and power to a target recipient such as a high-altitude platform. The NRC and our collaborators have also developed a range of modelling tools, components and modules to enable these demonstrations, including mid-IR sources and detectors, mid-IR optics for optical ground stations and photonic power converters.

For systems to be able to provide broadband services to remote regions that rival the services in urban areas, the HTSN Challenge program recognizes that the capacity of individual satellites to process data must be significantly improved. However, while current satellite technology relies on millimetre wave electronics and copper wire communications to store and move data on board satellites, current earth-based systems use photonics to overcome the data handling limitations of electronic and copper-wired systems. The objective of this research area is to develop on-board photonic circuit technologies that will significantly improve the data handling and data delivery capacity of satellites, and minimize the cost of producing and operating satellite systems. Initially, researchers will focus on a few key circuits:

• Optical beamforming networks (OBFNs) to control phased array antennas
• Optical phased arrays (OPAs) to precisely direct light beams over long distances
• High-capacity transceivers (TRx) to move data very quickly between 2 points inside a satellite

This research is being conducted in an HTSN Challenge program collaboration with McMaster University, MDA Space, Carleton University, Optiwave, Axonal Networks, Concordia University and McGill University.

One of the challenges in free-space communications is the effects of atmospheric disturbances on the laser beam. This atmospheric turbulence comes from fluctuations in temperature, pressure and moisture content that distort the laser beam as it propagates in the air. In order for the information carried by the laser signal to be readable, the beam must be restored to its original state before it reaches the detector. The adaptive optics research area focuses on the development of systems that can sense the distortions caused by the atmosphere and correct them. Examples of approaches being explored include photonic circuits that can sense and correct the beam, deformable mirrors and compressive sensing techniques. This research is being performed through HTSN Challenge program collaborations with the University of Toronto, the University of Manitoba, McMaster University, Optiwave and MDA Space.