A double-ring Mach–Zehnder interferometer sensor with high sensitivity

We theoretically proposed a cost-effective refractometer sensor, which includes an unbalanced two-ring Mach–Zehnder interferometer and can exhibit sharp asymmetric Fano lineshape. Our calculated results show this device has high sensitivity and can measure refractive index change in one of the resonators down to 10−9 refractive index units, which is two orders of magnitude higher than previous Fano lineshape based sensors.