Przemyslaw Falak

Speckle-pattern interrogation offers a route to high-resolution spectral sensing, but its uptake has been constrained by poor temporal stability under real-world conditions. Here, we introduce an ultra-stable speckle-based architecture that overcomes these limitations and enables real-time structural health monitoring of uncrewed aerial vehicles. Unlike conventional approaches that rely on large-scale, free-space passive speckle decorrelation, our system utilizes an ultra-compact speckle pattern via laser-written scattering centers in a high aspect ratio flat fiber, encapsulated within a 3D-printed polylactide housing. This architecture suppresses environmental drift and enables robust, high-fidelity interrogation of fiber Bragg gratings in dynamic aerospace conditions. The system demonstrated exceptional stability under sustained mechanical excitation, maintaining measurement integrity at ±7 G sinusoidal acceleration along the axial direction. Furthermore, in-flight validation across uncrewed aerial vehicle flight tests confirmed real-time strain interrogation in the −100–400 µε range with a standard deviation in measurement of 1.63 µε. These results mark the demonstration of stable, real-time speckle-based interrogation in flight, establishing a path toward broader deployment of specklemeters in harsh environments.

The development of ultra-compact lightweight optical instrumentation that can be used on-machine and to carry out in-process measurements is vital in realizing improved manufacturing processes, increasing the quality of parts being made while saving time and energy by reducing scrappage rates. Only incremental progress is being made in developing suitable instrumentation based on conventional components such as traditional refractive elements as fundamental limits in terms of size and weight are already reached. Here we demonstrate a chromatic confocal sensor that utilizes the natural chromatic aberration found with a basic hyperbolic metalens to realize an ultra-compact and simple probe. Further, we demonstrate how this can be combined with a compact specklemeter as the detection element, thus realizing the whole sensing system in a compact manner. Even with the proof-of-principle instrument in its preliminary and unoptimised state we achieve the successful recovery of the location of a scatterer as it is scanned over a 227 μm range, with a standard deviation of error in the position of 1.37 μm. Sensors of this form can be deployed in areas where traditional instrumentation would typically impede the manufacturing processes, increasing the number of processes that can have metrology applied directly and providing real-time feedback to improve manufacturing outcomes.

We demonstrate a reconstructive distometer with 0.78 micron resolution and 2.5 cm cubic footprint, utilising an engineered metalens and laser-written scattering medium for tailored speckle pattern generation, benefiting from low-cost, compact size and high stability.

Random scattering of light in disordered media can be used for highly sensitive speckle-based wavemeters and spectrometers. However, the multiple scattering events that fold long optical paths within a compact space also make such devices exceedingly sensitive to vibrations and small disturbances to the disordered media. Here, we show how scattering can be engineered so that it can be used for a compact computational spectrometer that is largely insensitive to environmental factors. We designed and fabricated a three-dimensional pseudo-random nano-void pattern with 62% scattering efficiency. The controlled amount of multiple scattering ensured a sufficiently long optical path for the target resolution of 100 pm, with optimal long-term stability. The 200-μm-thick scattering silica substrate was integrated in a compact assembly with a low-cost camera sensor. The target resolution was achieved for full spectrum measurements while single wavelengths could be determined with 50 pm resolution. Such tailored scattering systems can improve the trade-off among cost, size, stability, and spectral resolution in computational spectrometers.