Two-peak envelope spectrum of a subwavelength grating microring resonator for wide-range and high-sensitivity refractive index sensing

The detectable range and sensitivity play a key role in the accuracy and range of applications available for lab-on-a-chip sensing systems. Here, we propose and numerically demonstrate an on-chip refractive index sensor simultaneously possessing wide detectable range and high sensitivity through monitoring the two-peak envelope spectrum of a subwavelength grating microring resonator. The principle lies in the combination of the envelope spectrum tracking scheme and the light field releasing in subwavelength grating waveguides. The structure of the subwavelength grating microring resonator is designed to adjust the wavelength dependence of its critical coupling condition, so that the two-peak envelope spectrum can be formed and centered at critically coupled wavelengths. By probing the drift of the two-peak envelope spectrum within the C+L band (1530–1625 nm), we lift the free spectral range constraint on the detectable range and broaden it up to 0.46 RIU. Meanwhile, a sensitivity of 444 nm/RIU is achieved. This investigation provides an attractive candidate for high performance integrated sensors, and thus may pave the way for lab-on-chip sensing, especially in application scenarios demanding both wide detectable range and high sensitivity.