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Hollow waveguides catch ESA’s eye

24 Oct 2006

Hollow waveguides that eliminate alignment issues could be deployed on satellites in the future.

The European Space Agency (ESA) has awarded UK-based QinetiQ a EURO 310,000 contract to investigate the potential of its hollow waveguide technology for space-based sensors. If successful, the research could be deployed on micro-satellites to help improve weather forecasting and monitor climate change.

Mike Jenkins from QinetiQ’s Optronics Centre explains that the concept is essentially the optical equivalent of an electronic printed circuit board. The optical motherboard contains a network of hollow waveguides and discrete optical components all located on a common substrate.

According to Jenkins, this approach has several inherent advantages. “Each optical component is placed in an alignment slot formed on the substrate,” he told optics.org. “Light is then guided between the components in the hollow waveguides. As a result excellent alignment is achieved and maintained. The use of alignment slots also removes the need for heavy, bulky and expensive mounts for each component, which leads to much more compact, rugged and lower mass systems.”

The focus of the 18 month ESA contract is to design and develop hollow waveguide motherboards based on low-cost silicon and glass-ceramic substrates. The next step will be to demonstrate LIDAR and spectrometer systems by integrating all the required components onto the motherboard.

QinetiQ has previously used standard milling techniques (CNC) to produce a LIDAR subsystem composed of 11 discrete components. The overall system was approximately 100 x 100 x 30 mm with each component being 20 x 20 mm and 4 mm thick. The waveguide channels were 2 mm in cross section.

“For the ESA contract, one of the things we are exploring is miniaturisation based on the use of deep reactive ion etching (DRIE) of silicon substrates,” said Jenkins. “Now we are talking about producing waveguides with cross sections on the order of tens to hundreds of microns. We will also use DRIE to form alignment slots for components that might be 1 x 1 mm across and just 0.5 mm thick. We are looking at incorporating tens of components. DRIE gives you tight tolerances of +/- 0.5 microns in terms of lateral resolution.”

The ESA LIDAR system will operate at a wavelength of 1.5 microns, although Jenkins adds that the hollow waveguide technology offers a very broad transmission window. “You can go from UV to the far infrared,” he said. “The broad waveband means that the miniaturised silicon technology can be tailored to specific wavelengths. Compared with solid-core waveguides, the hollow waveguides can also carry much higher powers.”

The goal for QinetiQ is to see if it can transfer its success using milling techniques to produce compact, rugged, low mass optical circuits for space-based optical instrumentation.

“There are challenges in various aspects of the implementation but none are insurmountable, and there is a big pay off,” concluded Jenkins. “The upshot will be a fundamentally new approach to manufacturing optical and laser systems composed of any set of discrete components.”

Jacqueline Hewett is editor of Optics & Laser Europe magazine.

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