Interrogation of photonic biosensors using optical frequency combs

In this contribution, we show how the stability and ease-of-use of an integrated interferometric photonic biosensor platform can be enhanced using optical frequency combs, without any necessary changes to the sensor chip design. We show that if the comb line spacing of the optical frequency comb is adjusted to be at 120° intervals of the periodic spectral response of the used Mach-Zehnder interferometer and the transmission power values of the three comb lines are recorded over time, it is possible to extract the interferometer phase linearly and continuously for every sample point. This measurement approach provides an accurate phase measurement and is independent of the interferometer bias. Furthermore, it is robust against intensity fluctuations which are common to all three used comb lines. Our demonstration uses a simple silicon photonic interferometric refractive index sensor, and we show that the benefits of our approach can be achieved without degrading the lower limit of detection of 3.70×10^-7 RIU of our sensor platform. Our technique can be applied to any interferometric sensor and only requires a single input and single output and does not need any special couplers. This technique offers a drop-in replacement to the commonly used single wavelength phase measurement.