High-capacity Free-space Optical Communications with Orbital Angular Momentum

As the demand for high data returns from space science missions continues, significant improvements over the current radiofrequency (RF) communications architectures will be a necessity. Although current NASA Ka-band communications systems provide data rates up to 800 Mb/s and new developments in RF communication technology such as cognitive radios and arraying concepts may provide an additional order of magnitude improvement, free-space optical communications provide access to an uncrowded portion of the spectrum and can support data rates required by next generation science instrumentation. Achieving higher data transmission capacity is of primary interest and can be accomplished in optical communications through multiplexing multiple independent data channels, with potential data transmission capacity in the 100s of Gb/s or more - several orders of magnitude over what is capable using RF technologies. In addition to providing higher data transmission capacity, next generation communications platforms will need to reduce the size, weight, and power (SWaP) required to produce and sustain high rate transmissions. Free-space optical communications offers certain SWaP reduction improvements such as the advantage of smaller apertures compared to RF systems, and more interestingly, the possibility of photonic integrated circuits (PICs) in which a number of optical/photonic devices such as lasers, waveguides, modulators, detectors, etc. are integrated into a single unit. Furthermore, it is also possible to combine electronics with PICs, thereby reducing SWaP even further and allowing for applications on miniature platforms such as CubeSats. Recently, capacity-increasing concepts such as multiplexing with orbital angular momentum (OAM) modes have gained tremendous interest in the optical communications community, and have shown great initial success. However, current OAM transmitters and receivers require bulky optical set-ups for the generation of OAM states needed for data encoding and sorting. Investment in the proposed technology is important because we propose a photonic integrated circuit solution that has potential to fulfill the vision of high-capacity data transmissions with substantially reduced SWaP, and offer this concept as a potential candidate technology for next generation Near Earth and Deep Space platforms. The goal is to develop technology that demonstrates a scalable approach to optical communications multiplexing with orbital angular momentum (OAM), using integrated arrays of photonic OAM mode generating and filtering structures.