High-Q width modulated photonic crystal stack mode-gap cavity and its application to refractive index sensing

An optical sensor based on One-Dimensional photonic crystal (1D PhC) stack mode-gap cavity has been designed, fabricated and characterized. By introducing quadratically modulated width tapering structure, a waveguide coupled 1D PhC stack mode-gap cavity with calculated Q-factor 1.74 x 10(7) and an effective mode volume 1.48(lambda/n(Si))(3) has been designed. This cavity has been used for sensing applications by immersing into water-ethanol mixture of different volume concentrations. Transmission measurement shows a quality factor as high as 27, 000 can be achieved for the cavity immersed in analytes. A sensitivity of 269nm/RIU has been demonstrated. (C) 2012 Optical Society of America