Optical waveguide humidity sensor with symmetric multilayer configuration

A polymer waveguide sensor with a symmetric multilayer configuration is fabricated and integrated, and its application in sensing low humidity concentration has been demonstrated. The sensor measured the induced optical phase changes when the water molecules diffuse into the polymer waveguide. Sensitivity of several parts per million humidity concentration is achieved. The sensor also supplies the absolute sign of the movement of the produced interference fringes, which offers an easy indication of the index changes (increase or decrease) in the sensing layer. This study demonstrates a very promising prospect to make a compact, disposable optical-sensing device with low cost for humidity sensing application.