5 January 2017 Silicon nitride directional coupler interferometer for surface sensing
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A silicon nitride directional coupler (DC) used to create a biosensing device is presented. The DC detects changes in the refractive index of the cladding ( n clad ) as changes in the relative output intensity. The DC length ( L ), n clad -dependent sensitivities of the DC, and preferred dimensions of the single-mode DC waveguides are obtained through numerical simulations. The performance of the DC is evaluated through end-fire coupling measurements. The intensities measured after varying the n clad using air, water, and glycerol solutions agree well with the fitting for a wide range of L values between 60 and 600    μ m , i.e., corresponding to 6 to 60 times the coupling length. The bulk refractive index sensitivity was investigated using glycerol solutions of different concentrations and was found to be 18.9 optical intensity units per refractive index unit (OIU/RIU). Biotin/streptavidin bindings were detected with a sensitivity of 60 OIU/RIU and a detection limit of 0.13    μ M , suggesting the feasibility of the DC for immunosensing.
© 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)
Kyohei Okubo, Kyohei Okubo, Ken Uchiyamada, Ken Uchiyamada, Kiyoshi Asakawa, Kiyoshi Asakawa, Hiroaki Suzuki, Hiroaki Suzuki, } "Silicon nitride directional coupler interferometer for surface sensing," Optical Engineering 56(1), 017101 (5 January 2017). https://doi.org/10.1117/1.OE.56.1.017101 . Submission: Received: 9 August 2016; Accepted: 12 December 2016
Received: 9 August 2016; Accepted: 12 December 2016; Published: 5 January 2017

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