Compared with the conventional strip waveguide, subwavelength grating (SWG) waveguide has an enhanced evanescent field penetrating deeper within the upper cladding and the propagation direction, and an increased light-matter interaction can be achieved, resulting in a larger optical loss simultaneously. We experimentally demonstrate a subwavelength grating ring resonator around 1310nm. In order to reduce the influence of optical loss in the subwavelength bus waveguide and ring waveguide, we optimized the ring resonator by scanning the gap between the ring resonator and bus waveguide when the silicon duty cycle is fixed. The results experimentally show that the maximum extinction ratio of 18.8 dB when the gap and silicon duty cycle are equal to 120 nm and 0.7 around 1310nm. The extinction ratio has a 4.2dB larger than that for the resonance around 1550nm, which marks an increase of 28.7% compared to the C-band micro-ring sensors, thus showing a potential for bio-sensing applications in Lab-on-Chip system.
Microring resonators on silicon-on-insulator substrate have been demonstrated to be promising in sensing applications. We study a microring resonator biosensor based on a novel subwavelength grating (SWG) waveguide structure, which consists of periodic silicon pillars in the propagation direction with a subwavelength period. In this structure, effective sensing region includes not only the top and side of the waveguide, but also the space in between the silicon pillars which is on the path of the propagation mode. This leads to greatly increased bulk refractive index sensitivity as well as extended surface sensing region with constantly high surface sensitivity.
Subwavelength grating (SWG) ring resonators have demonstrated better sensitivity compared to the conventional silicon strip ring resonators due to the enhanced photon-analyte interaction. As the sensors are usually used in absorptive ambient environment, it is extreme challenging to further improve the sensitivity of the SWG ring resonator without deteriorating the quality factor because the coupling strength between the bus waveguide and the circular ring resonator is not sufficient to compensate the loss. To explore the full potential of the SWG ring resonator, we experimentally demonstrate a silicon-based high quality factor and low detection limit transverse magnetic (TM) mode SWG racetrack resonator around 1550 nm. A quality factor of 9800 is achieved in aqueous environment when the coupling length and gap are equal to 6.5 μm and 140 nm, respectively. The bulk sensitivity (S) is ~429.7 nm/RIU (refractive index per unit), and the intrinsic detection limit (iDL) is 3.71×10-4 RIU reduced by 32.5% compared to the best value reported for SWG microring sensors.