This invention is directed toward joining, with glass, a waveguide supported by a substrate to an optical fiber. In a preferred embodiment, a glass material which melts at a temperature that is lower than the temperature to which the waveguide can be safely heated is applied to either the optical fiber and/or the waveguide. The glass material is then heated to cause it to connect the optical fiber to the waveguide. A feature of the invention is the presence of heat breaks in the substrate upon which the waveguide resides to thermally isolate the end of each waveguide and the underlying substrate from adjacent waveguides and the portions of the substrate which underlie said adjacent waveguides. The heat breaks restrict heat from being conducted along the end of the substrate from one waveguide region to adjacent waveguide regions when heat is being applied to make a connection.