Photonic lanterns used in spectroscopy breakthrough

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Physicists at Heriot-Watt University and the Universities of Bath and Edinburgh in the UK have broadened the potential applications of time-stretch spectroscopy by increasing its detection capabilities by over two orders of magnitude. The breakthrough was reported in Nature Communications at the end of January.

Time stretch spectroscopy has previously been used to measure the colours of light that form optical pulses instead of using bulky and expensive instruments. Until now, however, the technique has had limited applications outside the lab. 

‘Conventionally, time-stretch spectroscopy has used single-mode optical fibres, where the light is guided in a single high refractive index core region in the middle of the fibre,’ said Heriot-Watt’s Professor Robert Thomson. ‘Unfortunately, the use of these fibres severely limited the real-world applications of this technique.’

Professor Thomson and his team have created a new way to analyse these colours, using multicore optical fibres, photonic lanterns and single-photon-sensitive detector arrays.

‘Time-stretch spectroscopy relies on the fact that the different colours of light that form an optical pulse travel at different velocities in an optical fibre,’ explained Thomson. ‘By measuring the arrival times of individual photons at the opposite end of the fibre, we can infer the colours of the individual arriving photons, and construct the spectrum of the input pulse.’

The researchers showed in Nature Communications that multicore fibres and advanced single-photon sensitive detector arrays can be used to perform multiplexed time-stretch spectroscopy, where 100 individual single-mode channels can be detected and processed simultaneously.

‘Crucially, we have also demonstrated that advanced photonic devices, known as photonic-lanterns can be used to efficiently couple light from the real world to these multicore fibres,’ continued Thomson. ‘This is a key step that holds great promise for real-world applications.’

According to Thomson, the multiplexing technologies reported have the potential to increase the achievable efficiency of time-stretch spectroscopy, enabling new applications such as highly sensitive spectrometers for pathogen detection, and photon-number resolving detectors for quantum optics.