2 × 2 single-mode zero-gap directional-coupler thermo-optic waveguide switch on glass

A 2 × 2 single-mode thermo-optic waveguide switch fabricated on a glass substrate is reported. The device uses a zero-gap directional-coupler configuration with a heater electrode to increase the waveguide index of refraction by the use of the thermo-optic effect. With an interaction length of 6 mm and using 0.63-µm He-Ne laser light, the device experiences a complete switchover of light from a straight-through channel to a crossed channel at an electrical drive power of 0.25 W under a quasi-steady-state condition and 0.67 W under a pulsed condition of 800 -s in pulse width. The device response is independent of light polarization and insensitive to ambient temperature. Transient thermal analysis is carried out with a two-dimensional transient temperature solution derived previously [IEEE Trans. Components Hybrids Manuf. Technol. 13, 980 (1990)]. A thermo-optic equation is established to relate the optical intensity to the temperature rise in the waveguide. The deduced optical responses based on the thermo-optic equation and the calculated thermal response agree extremely well with the measured responses, thus verifying the thermo-optic equation and the thermal-analysis method. We also confirm the fundamental principle of the zero-gap directional coupler and find that the 2 × 2 single-mode switch will be a useful component in future fiber-optic and integrated-optic systems.