Researchers Build Interferometer with 0.4° Field of View

Ramy Tannous and colleagues at the Research Council of Canada and the University of Waterloo have demonstrated a field-widened, multimode interferometer utilising a Herriott cell design. The prototype achieves a path length difference of 12ns while maintaining a 0.4° field-of-view, offering a passive and compact alternative to adaptive optics. The team created a new interferometer design that simplifies free-space optical communication, a method of transmitting data wirelessly via light.

The device successfully maintains a clear signal despite atmospheric disturbances, offering a potentially simpler alternative to systems needing constant adjustments. The prototype generates a substantial 12 nanosecond delay in the optical signal while preserving a wide 0.4° field of view, representing progress towards practical long-distance data links. Ramy Tannous and colleagues at the Research Council of Canada and the University of Waterloo have developed a new interferometer design to simplify free-space optical communication, a wireless data transmission method utilising light.

Maintaining signal quality over distance typically demands complex adaptive optics to counteract atmospheric disturbances, however, this team has created a passive and compact alternative. Their prototype employs a Herriott cell, which functions like a hall of mirrors, bouncing a light beam repeatedly to effectively lengthen its path without increasing the device’s physical size. The team’s innovation raises a key question: can this simplified approach deliver the performance needed for practical, long-distance data links without the complexities of adaptive optics.

Compact Herriott cell interferometer extends time-bin separations for secure communication

A prototype interferometer developed by the team achieved a path length difference of 12ns, surpassing previous limitations restricting such delays to systems requiring complex and often lossy adaptive optics. This breakthrough enables long time-bin separations, important for secure communication, within a remarkably compact device, a feat previously unattainable without sharply increasing system size and complexity. The design utilises a Herriott cell, a multi-pass optical system that folds the light path to create this substantial delay while maintaining a wide 0.4° field-of-view, effectively mimicking a much longer physical path without associated spatial constraints.

This passive approach offers a potentially simpler and robust solution for free-space optical links, particularly those susceptible to atmospheric turbulence and demanding high interference visibility with multimode beams. The prototype interferometer demonstrated a substantial 12ns path length difference alongside high interference visibility for spatially multimode beams. Detailed analysis, utilising both numerical ray-tracing simulations and a matrix analytical approach, confirmed the design maintains this performance across a 0.4° field-of-view; the optimisation process ensured the system behaved similarly to a flat mirror, vital for accurate beam alignment.

The team employed Gaussian Beamlet Decomposition, a technique modelling wavefront distortions and polarisation, for further verification, revealing high-quality destructive interference even with complex, multimode beams, as. Unlike a conventional Michelson interferometer of comparable path delay, which degrades with angular or spatial mode changes, simulations showed visibility remained consistently high.

While these results validate the design’s potential, the team acknowledges that practical implementation requires addressing aperture clipping effects and the geometric limits of standard optical components, meaning a fully deployable system remains some way off. Free-space optical communication demands increasingly sophisticated methods to counter atmospheric turbulence, and the team present a passive interferometer as a potential simplification of current adaptive optics systems.

Nevertheless, quantifying interference visibility is not always essential at this early stage of development, despite the abstract relying on the descriptor “high”. The researchers demonstrated a prototype interferometer utilising a Herriott cell, a system of mirrors folding light to create a long path in a small space, achieving high interference visibility. This arrangement of mirrors allows for a substantial delay within a compact footprint, offering advantages over traditional methods. The demonstration of a working prototype is a strong step forward in free-space optical communication, establishing a new benchmark by demonstrating high interference visibility with complex, multimode light beams despite significant time delays. A novel design employing a Herriott cell, a multi-pass optical system that effectively extends the path of light within a compact device, achieved this, circumventing the need for bulky and energy-intensive adaptive optics typically used to correct for atmospheric disturbances.

The researchers successfully demonstrated a field-widened, multimode interferometer capable of maintaining high interference visibility with complex light beams. This design utilises a Herriott cell to create a 12 nanosecond path length difference within a small device, offering a potential alternative to adaptive optics systems for free-space optical communication. Maintaining visibility across a 0.4° field-of-view suggests the system is less susceptible to disturbances than conventional interferometers. The authors note that further work is needed to address aperture clipping and geometric limitations before a fully deployable system can be realised.