FEATURE PORTABLE SPECTROSCOPY
gShowcase Award in Grenoble, France at the SEMI European MEMS and Sensor Summit
2017.
‘The NeoSpectra Micro was developed to bring spectroscopy even more so into the hands of consumers at a much lower price tag,’ said Smyser. ‘We’ve been able to do this through further optimisation of the optics and electronics, for example as opposed to using fibre to connect the MEMS chip to photodetector and the connector – as was done in the NeoSpectra module – we’ve instead gotten rid of the fibre and are now using plastic optics with mirrors.’ There are three pieces to the NeoSpectra
Micro: The optical core module, consisting of the monolithic single-chip interferometer and a single element uncooled InGaAs photodetector; a proprietary ASIC; and an optical head – a mini optical structure for sample illumination and the collection of diffuse reflected light. ‘When a customer used the NeoSpectra
Module to produce portable devices, they had to design their own light source and sampling interface, this has now all been integrated into the NeoSpectra Micro,’ Smyser said. The NeoSpectra Micro has a spectral
range between 1,350nm and 2,500nm and a resolution of 16nm, which is not as high
“We have invented a new packaging and assembly process that enables us to bring the laser onto the chip, which is one of the big challenges with silicon photonics”
resolution as a benchtop device, but is still enough to enable inline applications on portable consumer devices, according to Smyser, who explained that the device has already been designed into an iPhone case and used to perform tasks such as identifying the gluten levels in flour, or caffeine levels in coffee. ‘In the future consumers could use it to detect potential allergens in their food,’ he said. SWS also sees potential for the
technology in wearable medical devices, as non-invasive biochemistry measurements can be performed using NIR spectroscopy, for example measuring blood glucose and alcohol levels. ‘As we continue to bring down the size and cost of spectroscopy with our spectral sensors, we’re enabling new applications and new use cases across multiple industries,’ Smyser confirmed. ‘What we will find is a lot of new applications
24 Electro Optics March 2018
Fused silica wafer with photonic crystals. The photonic crystals are the same but appear different colours because of the variation in viewing angle
developing as this technology gets out.’ SWS intends to shrink its spectral
technology even further, with plans for a NeoSpectra Nano already on the company’s roadmap – a cheaper, smaller system that will be even easier to integrate into portable devices.
The increasing adoption of affordable
chip-level spectrometers could prove beneficial to the photonics industry as a whole, according to Smyser, as their use of components such as photodetectors, plastic optics and mirrors will provide a boost to the photonics firms supplying them, thanks to the high volume of orders expected for the new technology.
A crystal clear approach New York-based Chromation is taking its own approach to compact spectral sensing with the Chromation Spec, which, according to the firm, is the world’s first commercial photonic crystal spectrometer to be commercialised. ‘In the Chromation Spec, light travels
through a fused silica die where it is structured by mirrors and absorbers along a folded optical path to a photonic crystal, which creates spectral selectivity,’ explained Chromation CEO Nadia Pervez. ‘This die is assembled with a detector with a simple stacked alignment to make a spectrometer.’ According to Pervez, Chromation’s design is based around scattering spectroscopy rather than absorption spectroscopy, using a single element to divide the incident light into all constituent wavelength bands at
once. Scattering the incident light removes the need to re-image the input, while creating a spectrally selected output, as is the case with Czerny-Turner spectrometers, according to Pervez, which have to instead collect, collimate and reimage incoming light. In addition, by using non-imaging photonic crystal, less precision glass is needed, according to CTO John Kymissis, reducing the overall size and cost. The features of the Chromation Spec
are defined using wafer scale optical lithography processes and dry etch, Pervez noted. Fused silica was chosen for the substrates as it is transparent from UV to NIR, and is compatible with silicon production lines, she explained. While the current generation of the
technology offers broadband UV/VIS/NIR response from approximately 300-1,000nm, Chromation has already demonstrated its approach out to 10µm.
‘Similar designs can be used for longer
wavelengths, outside of the fused silica transmission range, but they require other materials and processes,’ Pervez explained. ‘The choice of detector also becomes an issue – at a minimum you need to consider the value proposition of an inexpensive optical die matched to an expensive detector.’ While the Chromation Spec is currently
offered as an evaluation board measuring 21 x 9 x 4.5mm, Chromation’s roadmap includes a chip version of the technology to address the growing demand from mobile, wearable and disposable applications along
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