SRI’s light emitter arrays aim to democratize optical communication among “constellations” of small satellites.
Already in the skies overhead, the large, expensive satellites of old are being replaced by groups of smaller, less expensive satellites working to accomplish many goals at once. A considerable challenge is that these satellite networks need to communicate with one another across the great distances of space.
The most promising space communication technology on the horizon is to beam data back and forth using light. Scientists at SRI are focused on building thin optical arrays that are smaller in size, weight, and power, or SWaP, that meet the technology challenges of ultra-high-speed inter-satellite communication.
“One of the major hurdles is to create a large diameter beam, but to keep energy demands and weight to a minimum,” said Nicole Heidel, a research engineer and photonics expert in SRI’s Applied Physics Lab. The SRI team has developed a new optical communication telescope that includes a photonic integrated circuit to create a large-aperture optical phased array — OPA for short — on a thin silicon wafer that is super lightweight while improving beam quality and reducing control complexity.
Paradigm shift
“Our approach delivers ultra-compact telescopes that make communication among the multi-terminal CubeSat and SmallSat space networks of the future possible,” Heidel said.
Unlike pencil-thin laser beams most are familiar with, like those in a laser pointer, the beams in SRI’s technology are almost five centimeters in diameter — about two inches — and include an array of 64 smaller emitters whose light adds up to a wide, strong beam. The width of the beam is critical in communications, helping receivers acquire and maintain contact with signals from other satellites in the constellation while reducing light loss that can degrade the signal over long distances.
“One of the major hurdles is to create a large diameter beam, but to keep energy demands and weight to a minimum.” — Nicole Heidel
Split and amplify
Technically speaking, the SRI OPA splits light from a single fiber-optic cable and steers the split beams to the array of 64 optical emitters with individual phase control. Because of the precise phase control of each emitter, the array can emit one single large and robust beam. Unlike other OPAs that make very small emitters achieve wide-angle beam steering, SRI targets large emitters to achieve larger area emission.
“This approach allows us to achieve a high-quality beam that can travel the long distances required in space. It also allows for reduced complexity leading to an ultra low size, weight, and power telescope that is so thin as to be essentially two-dimensional.”
It is extremely energy-efficient to boot. All the phase shifters in the five-centimeter aperture telescope combined use less than a single watt of power in total. The SRI telescope can even actively spread and steer the outgoing beam to help cooperating satellites acquire and maintain signal contact.
New approach
SRI’s architecture does away with existing technology’s need for the larger optics necessary to expand the beam, plus other optical controls and the support structure and housing that make traditional telescope assemblies so bulky, inefficient, and expensive.
SRI’s telescope’s optimal size and weight make it compatible with current and future beam steering mechanisms, Heidel says, and has the potential to reduce the size and weight of steering subsystems.
“We believe the architecture can eventually expand to larger apertures of 10 centimeters or more without significantly increasing thickness of the optical array and we are working toward that goal,” Heidel says, hinting at the directions of her ongoing research.
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SRI has a long history of contributing to the development and deployment of small CubeSat satellites. This includes advancements in satellite communications, space navigation, and miniaturized sensors, enabling the use of CubeSats for a range of applications, such as earth observation, space weather monitoring, and scientific experiments. Learn more about our work in space.
