A compact photodetector for an optical waveguide that is easy to integrate is necessary for optical on-chip devices. We demonstrate that a metallic contact covering an optical waveguide can monitor guided light in the 680 to 1550 nm wavelength range without blocking it. The contact is made of Au, titania, and Ti thin films that form a metal–insulator–metal structure. A concise design and facile fabrication process make our device particularly suitable for optical waveguides made of insulators such as polymers and dielectrics.

doi: 10.7567/APEX.9.122201