Dielectric overlayer for polarization discrimination in KTP channel waveguides

A 2-microm-thick dielectric film with a refractive index of 1.81 was deposited upon a KTP substrate containing channel waveguides fabricated by ion exchange. The resulting composite structure guided TM modes in the ion-exchanged KTP channel and TE modes in the dielectric film. The spatial separation of the guiding regions and the weak lateral confinement of the TE modes in the dielectric overlayer result in a greater round-trip loss for TE-polarized light when this composite waveguide structure is placed in an extended-cavity GaAlAs laser. This condition is sufficient to force the extended-cavity laser to oscillate in a TM mode, as required for frequency doubling of the diode-laser radiation in the periodically poled KTP waveguide.