In this work, a silicon oxynitride-on-silica refractometer is presented, based on sub-wavelength coupled arrayed waveguide interference, and capable of low-cost, high resolution, large scale deployment. The sensor has an experimental spectral sensitivity as high as 3200 nm/RIU, covering refractive indices ranging from 1 (air) up to 1.43 (oils). The sensor readout can be performed by standard spectrometers techniques of by pattern projection onto a camera, followed by optical pattern recognition. Positive identification of the refractive index of an unknown species is obtained by pattern cross-correlation with a look-up calibration table based algorithm. Given the lower contrast between core and cladding in such devices, higher mode overlap with single mode fiber is achieved, leading to a larger coupling efficiency and more relaxed alignment requirements as compared to silicon photonics platform. Also, the optical transparency of the sensor in the visible range allows the operation with light sources and camera detectors in the visible range, of much lower capital costs for a complete sensor system. Furthermore, the choice of refractive indices of core and cladding in the sensor head with integrated readout, allows the fabrication of the same device in polymers, for mass-production replication of disposable sensors.
Jaime Viegas, Mona Mayeh, Pradeep Srinivasan, Eric G. Johnson, Paulo V. S. Marques, and Faramarz Farahi, "Silicon oxynitride-on-glass waveguide array refractometer with wide sensing range and integrated read-out (Conference Presentation)," Proc. SPIE 10106, Integrated Optics: Devices, Materials, and Technologies XXI, 101060W (Presented at SPIE OPTO: February 01, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2254451.5393342284001.
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