novel tunable wave division multiuse (WDM) device has been formed on a microscope slide substrate. On the surface of the substrate is a K-ion-exchanged directional coupler with zero separation. On the top of the interaction region a Ti-film heater is placed. The operational behavior of the device is controlled by thermo-optical effect, and thus by the current through the Ti-film heater. Operational wavelengths designed for the device are 0.85 and 0.6328 μm. The measured results show that the device has predicted characteristics and thatthe design is reasonable.