Abstract
We performed numerical analysis and design parameter optimization of a silicon-based grating waveguide refractive index (RI) sensor. The performance of the grating waveguide RI sensor was determined by the full-width at half-maximum (FWHM) and the shift in the resonance wavelength in the transmission spectrum. The transmission extinction, a major figure-of-merit of an RI sensor that reflects both FWHM and resonance shift performance, could be significantly improved by the proper determination of three major grating waveguide parameters: duty ratio, grating period, and etching depth. We analyzed the transmission characteristics of the grating waveguide under various design parameter conditions using a finite-difference time domain method. We achieved a transmission extinction improvement of >26 dB under a given bioenvironmental target change by the proper choice of the design procedure and parameters. This design procedure and choice of appropriate parameters would enable the widespread application of silicon-based grating waveguide in high-performance RI biochemical sensor.
Highlights
Optical refractive index (RI) sensors that measure the change in RI have been proven useful in successfully developing a biochemical sensor that measures biomolecular interactions [1,2,3,4].These optical RI sensors exhibit significant advantages over conventional mechanical and electrochemical sensors
We recently proposed a compact and inexpensive biochemical sensor prototype using the Si-based grating waveguide to selectively detect and quantify the multivalent binding of proteins from a monovalent binding [19], which is known to be a critical step for better understanding of fundamental mechanisms in the immune system, cancer, and thrombosis [20,21,22]
We propose a method to achieve maximum transmission extinction by choosing appropriate grating waveguide parameters, which are the duty ratio, grating period, and etching depth
Summary
Optical refractive index (RI) sensors that measure the change in RI have been proven useful in successfully developing a biochemical sensor that measures biomolecular interactions [1,2,3,4]. The silicon-based grating waveguide RI sensor possesses two major advantages over other types of optical RI sensors These advantages are high-resolution performance in detecting changes in the RI and mass production capability regarding device fabrication. The former advantage is due to the shift of a sharp fringe in the transmission spectrum near the stopband edge of the grating [14], and the latter is due to a solid and matured processing technology of silicon (Si)-based electrical/optical device fabrication such. Our previous work and other studies on the Si-based grating waveguide sensor exhibit feasibility and high performance in detecting the changes in the RI of the target layer, the detailed analysis of the sensor performance considering the grating structure parameters and its design procedures have not been demonstrated yet. By using the procedure and with the optimization of the parameters, we achieved 49.2 dB of transmission extinction, which is an improvement of >26 dB when compared with the value attained without careful parameter selection
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