Silicon Subwavelength-Grating Microdisks for Optical Sensing

A silicon optical microdisk sensor for mid-infrared is proposed and demonstrated with subwavelength gratings (SWGs). This SWG microdisk is introduced to help obtain a high sensitivity. The bending radius is chosen as small as 6 μm to obtain a free spectral range of 40.3 nm enabling a large dynamic range of measurements. With the present SWG microdisk sensor, NaCl aqueous solution with a varied concentration is measured and the sensitivity is about 390.4 nm/RIU, which is consistent with the theoretical prediction.