This project plans to bring ideas and techniques from high-speed photonics and advanced telecommunications to bear on the field of optical communication systems operating through free space. Free-space optical communication systems emerged as the most promising alternative and supplement to high-speed radio frequency data links by offering several key advantages, such as higher security, operation over unlicensed frequency spectrum, and higher information capacity. Such systems can be remarkably well-suited for rapidly establishing high-speed communication in disaster recovery areas or over difficult terrains, linking Earth stations and low-orbit satellites, providing ultra-secure inter vessel connections, or supporting high-speed data links in urban areas. Although the information capacity of free-space optical communications is inherently higher since information is carried by frequencies from optical domain, there is need to investigate more comprehensive solutions for additional information capacity increase in order to advance high-speed free-space optical communication capabilities towards their full potential.
It is well known that higher information capacity can be enabled by exploiting fundamental optical parameters (time, frequency, polarization, and space) contained in a highly directed light beam. While the time, frequency, and polarization properties have been analyzed and understood in detail, theoretical and practical use of the spatial dimension is not fully explored. The goal of this project is to investigate free-space optical communication schemes by utilizing both frequency and space properties through their parallel employment within a single propagating light beam. Although this approach is highly promising, propagation through the turbulent atmosphere can drastically degrade the signal quality and thus reduce the information capacity. Therefore, an innovative approach is needed to advance solutions that can increase the information capacity and compensate for these turbulence effects.
The principal technical objective of the proposed project is advancement of technologically innovative multidimensional schemes that increase the information capacity of free-space optical communication systems. For that purpose, creation and propagation of spatial orbital angular momentum-based modes to carry an optimized number of spectral components will be explored. In parallel, modulation, coding, detection, and compensation schemes and algorithms that would maximize the information capacity of free-space optical communication channel will be investigated. This approach is transformative in nature since it brings multidimensional character to design of free-space optical communication channels. The key challenge in this task will be suppression and minimization of the mutual interaction between spatial modes due to the impact of air turbulence, which would otherwise cause unacceptable crosstalk and limit the channel capacity. For this purpose, a rigorous theoretical framework for the multidimensional free-space optical communication channel will be developed and experimentally verified. It will be used to lay down the crosstalk mitigation research tasks in both optical and electrical domains to counter the effects of long-term temporal correlation. A novel architecture that combines adaptive compensation of wave-front phase distortions with advanced detection and coding schemes and algorithms will be developed to suppress the impact of impairments caused by clear-air turbulence phenomena.
This program will help to transform high-speed free-space optical communication technologies in the United States by advancing the understanding and practicality of entirely novel communication schemes with a significant economic potential. In addition, the tight and creative interdisciplinary integration of knowledge and expertise in information theory and photonic technology will highly benefit undergraduate and graduate students at the University of Arizona, as well as those in the industrial research and development community.
