Boosting satellite networks with flexible microwave photonics

In a project with ESA, LioniX International has developed a reconfigurable microwave photonics module that could transform satellite communications. This innovation illustrates how far PIC technologies have come and how effectively they can now be adapted to serve a diverse range of industries.

By Sadoon Al-Obaidi, Marketing & Communications Director, Charoula Mitsolidou, Systems Engineer, and Ioana Mateciuc, Marketing Assistant, LioniX International

The ubiquity of generative AI in today’s world, both as a content-making tool and as a successful business case for PICs, has quickly become well-trodden ground. Of course, for industry insiders this is nothing new. Pluggable transceivers were already the biggest market for PICs before 2022, when popular software like DALL-E 2, Stable Diffusion, and ChatGPT were released for public use. For the PIC specialists, they are not where the intrigue lies. Instead, what everyone wants to know is: what will be next? Of all the possible applications of PIC technology, bursting with potential as it is, what device will combine the performance boost, market necessity, and ease of production to make the big time?

Will quantum computers finally take the crown from GPU computation? Is PIC-powered LiDAR on the verge of appearing in every car? How many disposable PIC sensors will personalised medicine need for rapid drug testing? Each of these applications requires entire ecosystems, with variations on product developers, design houses, chip foundries, assemblers, test labs, you name it. The technology is flourishing; if only we could know which of the many innovations will take off.

To be clear, we will not be consulting any oracles here. Aside from the Euro 2024 office pool, LioniX International is not in the betting business. But our module development work does make us regular optimists. We have seen design and processing principles, developed through more than 20 years of operation, prove capable of realising a range of disparate applications. We have converged on some basic rules to follow, like using each photonic integration platform for what it’s good at, designing the whole device before designing the photonic circuit, and involving the application experts as much as possible.

Figure 1. A general schema for satellite communication signal processing.

The PIC ecosystem has been arriving at the same conclusions, too. We now see a thriving PIC field, with many new and established firms following the same principles to tackle a wide range of problems from different angles. So, we are in no rush to have a horse in the race. Instead, our vertically integrated structure allows us to see the potential of PICs actualised for different markets, in novel modular devices, time and time again. Which brings us to the subject of this article: a particularly exciting recent in-house development in the form of a fully adjustable satellite communications (satcom) channel selector, functional across three microwave bands (Ka, Q, and V), from 300 MHz to 300 GHz.

Microwave communications is its own highly sophisticated field, rivalling even quantum processing in complexity and technical considerations. Diving into this world, we will explore how the function, design, and production of microwave communications come together, and how this technology can revolutionise satellite communications. But this is just one compelling example of a broader take-home message: PICs have reached a level of maturity that lets us build high-performance, energy-efficient devices for virtually every industry.

The question isn’t whether PICs can prove themselves again with a second killer app; the question is which market will be next to find its great leap forward with PICs.

Figure 2. Schematic representation of the 4-channel (DE)MUX filter module. The 4 independent paths leading out of the tuneable splitter each connect to an independent set of CROW and lattice filters. The power distribution is selected by the splitter, the CROW filters carve off the user-selected channel, and the lattice filters clean up the spectrum.

Crowded bandwidth, crowded orbit
The satcom industry faces an old monster in an evolved form. As telecom providers plan for bigger data rates through 6G networks and beyond, satcom must accommodate that need within a limited available bandwidth. There are a few options, but the industry has yet to converge on a solution for allocating the limited bandwidth where it is needed.

The status quo of satcom is that each conventional satellite is sent to orbit with a payload of electronics that processes signals in one specific way (Figure 1). They receive a low-power broadband signal from a ground station, which the satellite splits into different channels (demultiplexing, DEMUX). These component signals are frequency-shifted, filtered clean, then power-amplified separately, recombined into a single signal (multiplexing, MUX), and sent back to Earth.

This process of DEMUX, filtering, amplification, and MUX, is pre-programmed before the satellite is launched. The signal processing system is set, with no possibility of reconfiguring any of it once it is in orbit. If there is a signal that needs to be processed differently in some way, this can only happen if a different satellite equipped for the task is already launched into orbit.

One solution would be to populate space with as many satellites as necessary to handle the different processing routes. But there are many reasons why this would be far from ideal. Besides the high financial and material costs of launching so many satellites, this approach would clearly contribute to the serious problem of space debris, potentially triggering an ablation cascade – in which one collision results in more debris that makes further collisions more likely. Moreover, large numbers of satellites also interfere with astronomical research by simply blocking the view. The phrase “single-use satellite” may sound absurd, but the problem is inescapably reminiscent of plastic production and consumption.

The alternative is flexible satellites that can be reconfigured in orbit, ‘at runtime,’ to process different kinds of signals as needed. Far from trivial, this goal is a focus of much R&D effort in the space sector. The electronics of flexible payloads are difficult to realise, while the equipment required to do the necessary signal splitting, filtering, amplifying, and combining is bulky, heavy, and energy intensive.

For a reconfigurable electronic payload, the required components start to pile up, making the whole endeavour less efficient. But our emphasis on ‘electronic’ here is not incidental. ICs may be the original kind of integrated circuit, but PICs have exactly the right set of advantages to tackle this problem.