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Stratos Kehayas, PhD, G&H President of PhotonicsStratos Kehayas, PhD, G&H President of Photonics©️ G&H

Innovative design process fast-tracks UAV laser comms development


Author: Dr. Efstratios Kehayas, VP Research & Development

Establishing communication between air-to-ground, air-to-air and air-to-space using
photonics is increasingly attracting attention, due to the potential advantages related to transmission speed, low Size Weight and Power (SWaP) systems, spectrum regulation as well as immunity to electromagnetic interference.

Airborne communication platforms can be used for near real-time up/down-linking of time-critical information to ground stations or spacecraft in low or geostationary orbits. Inter-UAV or UAV to high altitude platforms such as pseudo-satellites can be used to set-up low-latency, high-speed data networks. Moreover, the motivation behind using free-space laser communications in the aerospace & defense sector is centered on establishing secure and reliable highspeed links in RF-denied environments for intelligence, surveillance and reconnaissance (ISR). Laser-based data links are inherently secure, immune to jamming and spoofing and transmission cannot be detected in contrast to traditional RF technology.

Considerable investment is driving the development of advanced airborne platforms capable of hosting payloads for diverse applications such as communication, sensing and security. The functionality offered by these platforms combined with the advantages gained with photonics technology has the potential to enable a completely new family of diverse bandwidth-hungry civilian or defence applications.

UAV in flightUAV in flight

Having identified satellite/UAV laser communications and space photonics as a key growth area, Gooch & Housego is addressing the market in a systematic way by developing application-specific sub-systems, underpinned by our considerable experience in the design and manufacture of aero- and space-grade components. Key building blocks of next-generation laser communication terminals and sensing equipment are realized by integrating these components into high-value systems. Within the frameworks of commercial and R&D contracts, we advance the state-of-the-art in fiber-optic modules in both sides of the Atlantic, taking advantage of the world-leading expertise we have in our core enabling photonic technologies.

Research and development of aerospace and space hardware is typically characterized by high cost and long timescales. The ability to innovate quickly and efficiently in order to demonstrate the potential of a technology through flight demonstrations is vital. In this way it’s possible to to gain insight into the possible initial performance, stimulate early interest, accelerate technology diffusion and reinforce subsequent commercialization phases. A prime example of the above rationale of quick route to flight is the recent development work carried out by G&H (Torquay) in close collaboration with Airbus Group in Newport, Wales. Under the auspices of the Aerospace Technology Institute (ATI) project called Airstart, we have been responsible for building a low SWaP high-power fiber optic Gb/s transmitter to be used for demonstrating UAV to ground laser communications. The challenges of mass and power targets, quick timescales and no margin for error, were counter-acted by the strong desire to push the performance envelope and think outside the box; characteristics and ambitions which resonate highly with our engineers across the G&H group.

UAV laser transmitter under test at G&H Torquay©️ UAV laser transmitter under test at G&H Torquay

The design phase of the laser transmitter required a rapid concurrent engineering effort between a multi-disciplinary team involving optical, electrical and mechanical engineers. In order to comply with the stringent performance and SWaP targets, the team had to optimize the optical performance of the system, employ G&H optoelectronic and fused components and use additive manufacturing for the mechanical parts. The system design relied on a novel G&H distributed feedback (DFB) laser requiring 50% less power to operate than conventional terrestrial-grade high-power DFB lasers, G&H HI-REL fused fiber couplers and a G&H high-power amplifier to boost the signal to multi-Watt levels. The mechanical and overall system design followed a holistic approach with ‘blurred’ boundaries between G&H and Airbus. This was imperative in order to generate a unit that would make optimal use of available resources in terms of mass, volume and power. Use of additive manufacturing resulted in a combination of plastic and metal parts for assembling and integrating fiber optic and electronic components. 3D printing also enabled heat management through structures otherwise not manufacturable with traditional CNC machining. Close collaboration, open channels of communication and multiple brainstorming meetings between the G&H and Airbus Group Innovations (AGI) teams were key in order to rapidly progress into the hardware development phase.

G&H laser transmitter; G&H laser and electronics board©️ G&H laser transmitter; G&H laser and electronics board

Having established key performance requirements, the laser transmitter was assembled and tested. Due to time and budget constraints, the team had a single shot in getting this right. The laser system was successfully assembled and tested at G&H in December 2016. Following preliminary performance testing and fit checks, it was transported to Airbus in Newport for system integration and further pre-flight electrical and optical evaluation. The Airbus laser pod containing the G&H laser transmitter successfully completed its maiden flight on 25 May 2017 on-board Southampton University’s Spotter UAV.

G&H UAV laser transmitter ready for transport to Airbus and G&H development team©️ G&H UAV laser transmitter ready for transport to Airbus and G&H development team (from left to right): Marios Kechagias (Engineering Technician), Matthew Welch (Photonic Systems Engineer), Stratos Kehayas (VP R&D), Richard Webb (Mechanical Designer), Liam Henwood-Moroney (Electronics Engineer)

The importance of this flight demonstration is three-fold. Firstly, from a technology point of view, it allows for a preliminary evaluation of the laser transmitter in the field, which will feed subsequent re-designs, optimization work and ultimately product development. Secondly, it demonstrates the upsides of G&H’s vertical integration capabilities, as the design and development of the system required components, modules and sub-systems from five different groups, in two different G&H sites in the UK and the US. Last but not least, it demonstrates that innovation in A&D can be efficiently achieved quickly and cost-effectively by establishing trusting links between small engineering groups within the organizations involved. The trigger for G&H and Airbus to start working together was the result of an informal meeting between the two team leaders that met at a DSTL event.

The first follow-up brainstorming session at G&H (Torquay) resulted in a one page target specification document that was the basis for kick-starting the activity. This document was actually drafted during the meeting from a blank piece of paper. The indispensable ingredient required for the project to work was there right from the beginning: mutual trust, team spirit and high level of dedication. Project meetings going through specification documents and compliance matrices, were substituted with open brainstorming technical meetings between engineers that shared the excitement of flying the systems they would design. Both teams took collective responsibility of the system as a whole and worked seamlessly to resolve the issues as they were arising, without focusing on contract boundaries and specification responsibilities. The G&H team is grateful to Yoann Thueux (AGI team leader), Gavin Erry (AGI Senior Scientist), Edward Kingston (EK Electronics Design Engineer), and Malcolm Watson (AVoptics Principal Research Engineer) for this smooth collaboration.

The short but intense experience with Airstart has vividly shown that facilitating innovation can sometimes equally relate to the business methodologies and company structures as well as to the actual technology challenges ahead. Maintaining small agile teams of motivated, capable and enthusiastic engineers within larger organizations can be key in order to foster innovation in the A&D sector and within medium/large industrial organizations.