Systems and methods for measuring a characteristic of a fluid are provided. The system includes a plurality of waveguides embedded in a substrate, and an exposed surface of the substrate comprising a portion of a side surface of at least one of the plurality of waveguides. The system also includes a sensitized coating in the at least one of the plurality of waveguides. The exposed surface is curved in a direction perpendicular to a light propagation in the waveguide. A method of fabricating a system as above is also provided.