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Sensors and Actuators B: Chemical, Volume 168, 20 June 2012, Pages 402-420
Vittorio M.N. Passaro, Benedetto Troia, Francesco De Leonardis
Photonics Research Group, Dipartimento di Elettrotecnica ed Elettronica (DEE), Politecnico di Bari, Via Edoardo Orabona n°4, 70125 Bari, Italy
Abstract
Nowadays, photonic gas sensors represent an attractive alternative for the detection of harmful gases, such as acetylene (C2H2), methane (CH4), ethane (C2H6) carbon monoxide (CO), carbon dioxide (CO2) and sulfure dioxide (SO2), for applications concerning home-safety, industrial needs and environmental gas monitoring. Among several technological platforms, optical sensing actually represents the most intriguing solution. In fact, incomparable advantages are enabled by photonic technologies, such as high sensitivities, ultra-low limit of detections, CMOS-compatibility, compactness, metal-free operation, low-cost and electromagnetic immunity. In this context, it is worthy to note that some harmful gases exhibit characteristic absorption lines in the mid-infrared (mid-IR) wavelength region, specifically in the range from 2 µm to 8 µm. For example, mid-IR absorption strength of methane is 160 times larger than that in near-IR. Consequently, photonic sensors, able to operate in mid-IR, represent a promising solution for the fabrication of integrated and miniaturized gas sensing photonic systems.
We present a generalized procedure for the design of photonic gas sensors, based on Vernier effect, in silicon-on-insulator (SOI) technology. In particular, a mathematical approach based on Mason’s rule and delay line signal processing has been considered for the modeling of photonic architectures based on multiple ring resonators. The proposed model has been validated and generalized by demonstrating the Vernier effect in mid-IR. An algorithmic procedure has been also implemented for selecting design parameters and criteria of integrated gas sensors mentioned above. Our procedure has been tested through simulations of two specific gas sensing examples, i.e. methane and ethane detection at 3.39 µm. Very efficient performances have been achieved in terms of ultra high wavelength sensitivities, larger than 200 um/RIU (refractive index unit) and limits of detection as low as 10-5 RIU, allowing the accurate detection of gas concentration traces in air volume, as low as 2 % – 3 %. Finally, the proposed method results to be highly flexible. In fact, it is possible to customize the design of photonic sensors as a function of the general gas sensing application, using the same generalized approach.
Actually, the Photonics Research Group at Politecnico di Bari (URL: http://dee.poliba.it/photonicsgroup) is working on further development of advanced photonic sensors based on silicon and its compounds, for ultra-high performance gas sensing in near and mid infrared.
Figure legend
Silicon photonic sensor formed by two cascaded ring resonators based on the Vernier effect in SOI technology for ultra-high performance gas sensing in mid-IR.
