Today, over 70 million organic and inorganic substances are on record, and for most of these, little is known about their potential danger to humans. Although only a small fraction of this plethora of molecules are marketed and released into the environment, our society is confronted daily with a growing number of potentially hazardous chemicals.
Already today, we possess the biochemical and technical means to identify small numbers of molecules or microbes in a sample. However, all these methods are expensive and time-consuming. Optical methods may provide breakthrough solutions to this highly relevant problem, overcoming the traditional, tedious chemical lab analysis. For example, it is known that measurement techniques in the mid-infrared (MIR) spectral range, known also as the fingerprinting/diagnostic region, are highly specific to individual molecules, even able to distinguish between isotopes in their atomic constituents.
Optical methods can also be extremely sensitive, exploiting the existence of photonic sensors capable of detecting the arrival of single photons with sub-nanosecond timing precision. Additionally, very sensitive and highly specific novel diagnostic techniques are emerging, such as Raman and LIBS spectroscopy, whose performance would be much improved if operation could be extended into the infrared spectral range. However, the major problem with the current photonic devices and detection systems capable of achieving the required specifications is that they are much too expensive for the realisation of affordable, practical sensing systems! Consequently, it is essential that multiband photonic sensing is developed, leading to a safer and more secure society. Once available, these photonic innovations will lead to numerous additional applications, further improving many aspects of our daily lives.
Major photonics needs
The near infrared (NIR) spectral range (0.8–2.5 μm) is already employed for many tasks in food inspection (moisture sensing, content of protein/oil /fat/starch/sucrose/fibres, detection of foreign particles and nut/fruit-stone inclusions, quality and ripeness of fruit and vegetables, etc.), as well as in recycling and waste treatment (sorting of wastepaper, cardboard, plastics/polymers, fuels, industrial waste). The diagnostic mid-infrared (MIR) region (2.5–7 μm) yields information about the presence of functional groups in samples, enabling, for example, the identification of numerous volatile organic compounds (VOCs) in gases. The fingerprint MIR region (7–11 μm) allows the different compounds in a sample to be distinguished, due to the specific spectral 'fingerprint' of each molecule in this spectral domain, utilising the large existing collections of reference spectra in vapour and condensed phases. Finally, the far infrared and THz region (up to 1000 μm) offers complementary fingerprinting capabilities using specific spectral signatures, with the additional benefit of deep penetration in standard packaging materials such as paper, plastics or textiles.
Some of these critical measurements in the extended infrared (EIR) spectral domain (1–1000 μm) can be performed today, albeit with very expensive active and passive photonic components. For example, a moderate-power MIR laser costs €10,000, an uncooled FIR bolometer camera costs at least €50,000, a 128x128 NIR image sensor (InGaAs) costs €4000, a single photodiode (InAsSb) for the 1–5 μm band costs €1000, and even a single silicon microlens (for wavelengths above 1.1 μm) costs €50. Clearly it is not currently possible to realise cost-effective EIR sensor devices and make them affordable for general use, despite the abundance of highly relevant practical applications operating in the infrared spectral domain. While the important ultraviolet and visible (UV/VIS) spectral domain is accessible using the ubiquitous silicon photosensors, we have to progress beyond silicon in order to meet the challenges of the EIR domain. The challenge is therefore clear – we need to develop new high-performance yet affordable photonic devices. Specifically:
- quantum-noise-limited active optoelectronic devices (coherent and incoherent sources,detectors) based on inorganic/organic semiconductor materials, offering the appropriateEIR properties.
- CMOS-based charge detector platforms with low-noise/low- power/high-speed-readout performance that can be combined with many classes of semiconductor materials.
- novel measurement techniques to exploit the beneficial properties of such newly developed EIR detectors for industrial applications.
- affordable non-toxic cooling solutions (in particular thermo-electric coolers) for EIR photosensing and light emission platforms
- a wide range of low-cost passive optical components, to enable the integration of complete EIR systems.
The overall goal is to conquer the EIR spectral range with a complete toolbox of low-cost active and passive photonic devices. These will be used to provide reliable, high-performance yet affordable diagnostics measurement methods and systems for professional and consumer use.
The detailed Photonics21 Work Group 5 photonics research and innovation priorities are outlined if you download the Photonics Roadmap.
You will find the Work Group 5 research and innovation priorities for Horizon 2020 Work programme 2016/2017 in the section Photonics PPP – Research and Innovation Priorities.
Information and presentations of the Work Group 5 workshops can be found in the Photonics21 member area.