Low-Loss Junctions between Dielectric and Metal-Clad Dielectric Waveguides

Metal-clad waveguides,1,2 metal-clad optical components3 and optical strip lines have many advantages for forming optical circuits. First, they can be formed on any substrate since the metal cladding isolates the optical fields completely from the substrate. Next, since the metal has a negative dielectric constant at optical wavelengths, a dielectric film of an arbitrarily low refractive index can be used for the waveguides. This is particularly attractive as most of the high-quality optical films, such as glass, organic silicon, and solution-deposited-polymer films, have relatively low refractive indices. Finally, metal-clad waveguides have losses on the order of 1 dB/cm in the TE m=0 mode, provided that the dielectric films used have thicknesses of 1 µm or larger. We had proposed earlier in our letter3 that metalclad waveguides, polarizers and corner-reflectors can be formed together with LiNbO3 optical scanners and switches on a common LiTaO3 substrate to form an integrated switching circuit.