A new technique for fabricating active planar waveguide devices is reported. This process, based on the thermal bonding of precision finished crystal or glass components, allows waveguides to be assembled from very dissimilar materials and could be applied to a wide range of solid state laser or other optical media. The waveguide propagation losses, inferred from the laser performance, are found to be 0.7 dB/cm forNd:Y3Al5O12bonded toY3Al5O12,Nd:Y3Al5O12bonded to glass, and 0.4 dB/cm forNd:Gd3Ga5O12bonded toY3Al5O12devices. ©1997 American Institute of Physics.