SOI-based centimeter-scale Mach-Zehnder interferometers for fluid sensing

In this work, we demonstrate centimeter-long Mach-Zehnder interferometers (MZIs) suitable for optical uid sensing applications, fabricated on a silicon-on-insulator platform through photolithography. The sensing mech- anism is based on the perturbation of the evanescent field of the optical mode in the sensing arm of the MZI by the measurand. We explore two different configurations for the MZI sensing arm, a partially exposed and a fully suspended, both defined as ridge waveguides with a 450 nm-wide and a 220 nm-thick ridge on a 90 nm-thick silicon slab. The partially exposed MZI arm has oxide under-cladding and air over-cladding, while the fully suspended version has its buried oxide locally removed through an isotropic etch. The MZIs are slightly unbalanced, with arm lengths around 1 cm. The sensitivity of the devices is evaluated through mode solver simulations, with values around 240 nm/RIU and 740 nm/RIU, for the partially exposed and fully suspended structures, respectively.