PORTABLE SPECTROSCOPY FEATURE


with extensions to longer wavelengths. Scaling down this technology is not


without its drawbacks, according to Pervez. ‘One of the trade-offs that we need to make in scaling down size is reduction in field of view,’ she explained. ‘The design rejects light outside of the target field of view, so it still is “point and shoot”. ‘It really depends on the application as to


whether the small field of view is a feature or a drawback. It means we don’t collect as much light, but the light we do collect is spatially resolved.’ ‘There are [also] trade-offs in throughput,


resolution, and size for all spectral sensing technologies,’ added Kymissis. ‘What we offer is the best approach at the miniature size scale; it’s as spectrometers scale up that other approaches start to surpass us in performance.’


Superior scaling Smyser, of SWS, explained that many spectroscopy players have been miniaturising their technology using discrete optics – reducing the size and amount of optics used – which can be quite limiting as discrete optics can’t really be scaled in terms of volume or cost. In a 2016 paper published by the Institute of Electrical and Electronics


Engineers (IEEE), Derek Kita, a fourth year PhD Candidate working at the Juejun Hu photonic materials research group at MIT, demonstrated that simply replacing the bulky discrete optical elements of conventional IR spectrometers with their on-chip counterparts, is not a viable route towards on-chip infrared spectroscopic sensing, as it cripples the system performance due to the limited optical path length accessible on the chip. ‘The primary issue with simply replacing components from free-space dispersive spectrometers with their on-chip (planar waveguide) counterparts, is that the spectral resolution of both dispersive and modulated (such as Fourier-transform) devices scales linearly with the device size, assuming a fixed spectral bandwidth,’ Kita explained. The MIT group has therefore designed


Spectroscopy_ad_189x129.qxp_Layout 1 22/02/2018 09:56 Page 1


its own method of performing on-chip spectroscopy that it calls digital Fourier- transform (dFT) spectroscopy. ‘This technique uses time-domain modulation of a photonic Mach-Zehnder interferometer to perform very high-resolution spectroscopy,’ said Kita. ‘Unlike other tunable Mach- Zehnder structures that use thermo-optic or free-carrier-dispersion effects to modulate the phase of light, our architecture


consists of a cascaded set of switches that physically alter the waveguide length difference between top and bottom interferometer arms. ‘With this architecture, each binary switch state corresponds to a unique measurement of the interferogram, so a simple 10-switch dFT spectrometer can offer 1,024 spectral channels, a figure that is already competitive with commercial free- space spectrometers.’ As with IBM’s, SWS’ and Chromation’s


chip-level spectroscopic technology, the MIT group’s dFT architecture can be readily fabricated with standard photonic building blocks available at most foundries. Other benefits include increased


temperature stability, picometre-level wavelength resolution, and a large signal-to-noise ratio improvement, according to Kita, whose group recently demonstrated successfully working dFT spectrometer prototypes working in the telecommunication wavelength range. The next step for the team is moving


towards fabricating and demonstrating dFT spectrometers at other wavelength regions that are relevant to chemical and biological detection, such as NIR for Raman spectroscopy, as well as mid-IR for absorption spectroscopy. EO


Mini, Micro and MEMS Spectrometers


Hamamatsu offers an extensive range of Mini, Micro and MEMS Spectrometers which cover the spectral range from UV to NIR. They are suitable for a diverse range of applications including medical devices, environmental and colour monitoring, food, agriculture


and chemical analysis, and more. To meet growing market demands we also offer an OEM micro-spectrometer head which can be easily incorporated into compact, portable measurement instruments.


Now with a line-up boasting more than 20 devices, you will easily find the optimum solution to bring your product concept to reality.


www.hamamatsu.com


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44