Silicon photonic biochemical sensor on chip based on interferometry and phase-generated-carrier demodulation

Integrated biochemical sensors based on Mach- Zehnder interferometers (MZIs) rely on the evanescent field detection principle to monitor the phase shift induced by a re- fractive index change on the surface of the sensing arm, providing a high sensitivity thanks to the long interaction length with the analyte. This paper presents an integrated refractive index and biochemical sensor based on a pair of balanced MZIs realized on silicon-on-insulator. The device includes a thermal phase modula- tor in one of the branches of each MZI to extract univocally the induced phase change by applying active phase detection based on the phase generated carrier technique. The direct modulation of the MZI results in a simple configuration of the sensor, only requiring a fixed wavelength laser and a photodetector, enabling the possi- bility of full monolithic integration. The results of refractive index measurements show a detection limit down to 4.88 × 10–7 RIU. Additionally, an immunoassay reports the binding of anti-bovine serum albumin (BSA) to BSA, with anti-BSA concentrations down to 33.33 nM.