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Silicon-photonics-based laser spectroscopy platform: towards a paradigm shift in environmental monitoring and health care

Final Report Summary - INSPECTRA (Silicon-photonics-based laser spectroscopy platform: towards a paradigm shift in environmental monitoring and health care)

A key challenge for the 21st century is to provide billions of people with sufficient fresh water and food and with a good health care and to do so in an intrinsically sustainable and affordable way. Given the finite resources, the change of climate, the fragility of the ecosystem, the increasing life expectancy and the growing world population the challenge is actually immense. Sensing and monitoring systems will be of ever increasing importance in this context, not only for governing bodies, communities and companies but also for individual citizens. Optical spectroscopy has a special role to play here, because it allows to detect and measure the composition of gases, fluids and solids in a precise, non-destructive and contact-less way. However conventional optical spectroscopy systems are often bulky and expensive. If alone it would be possible to integrate optical spectroscopy systems at low cost in portable and wearable devices, in smartphones, or even in bodily implants, the impact on point-of-care and preventive medicine, on food, water and air quality, on environmental monitoring etc could be expected to be massive.
The InSpectra Advanced ERC Grant project has focused on the development of on-chip optical spectroscopy systems. The heart of such a system is an optical chip – a photonic integrated circuit or PIC– fabricated with the mature technology base of the silicon microelectronics world. All optical functions, from light source and interaction with the analyte to spectroscopic functions and detectors are integrated on a small chip of a few tens of square millimeters. This approach holds the promise of making a wide variety of sensing and monitoring functions ubiquitous. This will eventually enable a situation where one will find one or several optical spectroscopy systems in every home, in every classroom, in every medical practice, perhaps as an implant in the body of every diabetes patient.
Key challenges in the development of compact on-chip spectroscopic systems include the integration of a low power light source as well as the collection of sufficient signal strength from weak processes such as Raman scattering or from ultra-low analyte concentrations. These challenges have formed the main focus of the project.
With respect to the integration of light sources on silicon-based photonic ICs we have demonstrated semiconductor lasers and broadband light sources (including comb sources) through the integration of III-V semiconductors with silicon-on-insulator or silicon nitride waveguide circuits. This was done for three distinct wavelength ranges: the 1550 nm ‘telecom’ band (relevant for glucose detection for example), the 780 and 850 nm band (relevant for Raman spectroscopy of biological media) and the short-wave infrared band between 2000 and 2500 nm (relevant for vibrational absorption spectroscopy). We have also demonstrated on-chip four-wave mixing based supercontinuum and comb sources in all these spectral bands.
In terms of on-chip spectroscopic systems we have demonstrated the sensing of ammonia down to sub-ppm level and the sensing of glucose down to physiologically relevant levels. We have conducted seminal work on on-chip Raman spectroscopy. We have demonstrated that waveguide-based on-chip Raman spectroscopy outperforms confocal Raman microscopes in terms of detection sensitivity. We have also demonstrated several implementations of waveguide-coupled surface-enhanced Raman spectroscopy (SERS). This latter work is very promising for single-cell analysis of key biological functions such as enzymatic response.
A last – and more fundamental - topic of research in InSpectra has been the exploration of frequency combs generated by opto-mechanical methods on a silicon chip. We have focused on Stimulated Brillouin Scattering and have demonstrated for the first time Brillouin optical gain in silicon waveguides.