Highly sensitive compact refractive index sensor based on phase-shifted sidewall Bragg gratings in slot waveguide

The geometrical and physical parameters of phase-shifted sidewall Bragg gratings in a silicon slot waveguide are optimized to possess performance characteristics desirable for integrated optical sensors. By tailoring the spectral response of such phase-shifted sidewall gratings, highly sensitive compact refractive index sensors detecting the resonance wavelength shift or the variation of light intensity are designed with the transfer matrix method. Both refractive index sensors have a minimum detection limit on the order of 10(-6), and a linear response and a compact structure dimension as small as 11.7 μm, offering the capabilities for sensor array and lab-on-a-chip integration. The resonance-shift sensor has a much wider detection range of 1.32 refractive index units than the intensity-measurement sensor. The performance parameters are compared with other refractive index sensors, including Mach-Zehnder interferometers, ring resonators, surface gratings, and phase-shifted gratings in silicon nanowire.