Interferometer-based chemical sensor on chip with enhanced responsivity and low-cost interrogation

We report experimental results of an interferometric chemical sensor integrated on a silicon chip. The sensor measures refractive index variations of the liquid that contacts exposed spiraled silicon waveguides on one branch of a Mach-Zehnder interferometer. The system requires neither laser tuning nor spectral analysis, but a laser at a fixed wavelength, and a demodulation architecture that includes an internal phase modulator and a real-time processing algorithm based on multitone mixing. Two devices are compared in terms of sensitivity and noise, one at 1550\&\#x2005;nm wavelength and TE polarization, and an optimized device at 1310\&\#x2005;nm and TM polarization, which shows 3 times higher sensitivity and a limit of detection of 2.24\&\#x00B7;10\&\#x2212;7 RIU.