  A micro-ring-resonator (MRR) optical biosensor based on the evanescent field
sensing mechanism has been extensively studied due to its high sensitivity and
compact device size. However, a suitable on-chip integrated spectrometer device
has to be demonstrated for the lab-on-a-chip applications, which can read the
resonance wavelength shift from MRR biosensors based on minuscule changes in
refractive index. In this paper, we demonstrated the design and experimental
results of the near-infrared lab-on-a-chip optical biosensor platform that
monolithically integrates the MRR and the on-chip spectrometer on the
silicon-on-insulator (SOI) wafer, which can eliminate the external optical
spectrum analyzer for scanning the wavelength spectrum. The symmetric add-drop
MRR biosensor is designed to have a free spectral range (FSR) of ~19 nm, and a
bulk sensitivity of ~73 nm/RIU; then the drop-port output resonance peaks are
reconstructed from the integrated spatial-heterodyne Fourier transform
spectrometer (SHFTS) with the spectral resolution of ~3.1 nm and bandwidth of
~50 nm, which results in the limit of detection of 0.042 RIU. The MRR output
spectrum with air- and water-claddings are measured and reconstructed from the
MRR-SHFTS integrated device experimentally to validate the wavelength shifting
measurement.
