Tunable guided-wave optical polarization converters using static strain-induced mode coupling in lithium tantalate

Guided-wave optical polarization converters in birefringent crystals are wavelength selective and are thus useful for wavelength-division-multiplexing applications. Several such components have been produced on LiNbO3 and LiTaO3 substrates by using electro-optic or acousto-optic interactions.1–3 Their operation, however, has required a continuous use of external power to sustain the polarization coupling. This paper reports the use of static shear strain to promote polarization conversion in a channel waveguide. The strain is produced by a spatially periodic surface film deposited at an elevated temperature and patterned at room temperature; it is induced from the thermal expansion mismatch between film and substrate. No external power drive is needed, and the conversion is highly wavelength selective. Both thermal and electro-optic tuning have been used to shift the wavelength of maximum conversion.