Printable multi-layer flexible foil system for integrated optical sensors

Integrated optical sensors based on waveguides allow for the direct detection of biomolecular or chemical interactions. The evanescent field of the propagating wave interacts with an analyte resulting for example in a change in intensity of a Mach-Zehnder interferometer.

To form a waveguiding system three different layers (lower cladding, waveguide core, upper cladding) are required to confine the optical wave both vertically and horizontally and shield it from unwanted environmental interaction. The refractive indices and the dimensions of the waveguiding structure determine the behavior in terms of guided mode number and sensitivity of the sensor. There are two main specifications that have to be met for sensing applications: single-mode behavior of the waveguides and high sensitivity meaning that the evanescent field has to reach as far as possible into the analyte.

Polymers are suitable for forming optical waveguides as they can be transparent, low loss and adjustable in refractive index and viscosity. Starting with a transparent polymer foil as substrate and lower cladding the subsequent layers can be applied using printing technologies like flexographic or inkjet printing using transparent polymer-based inks that can be cured using UV-light or temperature.

[458]