Chemical sensing is usually achieved in photonics platforms by monitoring spectral changes on the output of a passive photonic element due to the modulation of the refractive index of core and cladding. Therefore, compact interferometers are usually sought for the embodiment of refractometer sensors. We present our work on refractive index sensors based on arrayed waveguide interference, which are built on a Silicon-On-Insulator (SOI) platform. A comparative study of two configurations, resonant and non-resonant is presented. In both cases the main design is based on a set of closely placed single mode waveguides. The distance between waveguides is such that directional coupling occurs. Moreover, when the distance between the waveguides is small comparatively to the transversal exponential decay length of the eigenmode of the waveguide, there is an enhancement effect of the electric field in the region between the waveguides, as usually seen for slotted waveguides. The reported sensors include multiple parallel slotted waveguides which are the core of the sensor. Non-resonant configuration incorporates straight waveguides from which the output can be directly imaged onto a CCD array for direct sensor read-out, while the resonant layout presents a set of concentric racetrack waveguides designed for light extended lifetime, enhancing the sensor sensitivity. A top polymer cladding is used to encapsulate the waveguides providing a permeable low index material. This cladding material acts as the transducer element, changing its optical properties when in contact with a chemical of interest, therefore allowing for high sensitivity and chemical selectivity.
Ricardo Janeiro, Raquel Flores, and Jaime Viegas, "Silicon photonics waveguide array chemical sensor with integrated read-out (Conference Presentation)," Proc. SPIE 10107, Smart Photonic and Optoelectronic Integrated Circuits XIX, 101070U (Presented at SPIE OPTO: February 02, 2017; Published: 28 April 2017); https://doi.org/10.1117/12.2251939.5393342317001.
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