PPKTP

PPKTP stands for periodically poled potassium titanyl phosphate, a nonlinear optical crystal used to realize quasi-phase matching by periodically inverting its ferroelectric domain structure. The nonlinearity of KTP combined with periodic poling enables efficient frequency conversion and parametric processes that would be inefficient in uniformly poled crystals. PPKTP is widely used in research and applications spanning classical and quantum optics.

Potassium titanyl phosphate itself offers a broad transparency range from the visible to the near-infrared and favorable optical properties. By altering the poling period, orientation and temperature, designers can tailor phase matching for type-0, type-I and type-II interactions at target wavelengths. Poling periods are typically on the order of a few micrometres, and PPKTP devices are available as bulk crystals and as waveguides, enabling integrated photonics. Temperature tuning within a modest range provides fine control of the phase-matching condition.

Common applications include second-harmonic generation, sum- and difference-frequency generation, and optical parametric oscillation or amplification. In quantum optics, PPKTP is a popular source of photon pairs and squeezed light via spontaneous parametric down-conversion, often delivering high efficiency and good mode quality at telecom or near-infrared wavelengths. Compared with other periodically poled crystals, PPKTP offers robust performance at room temperature with relatively low photorefractive effects and good damage thresholds for many wavelengths, though the exact advantages depend on the operating regime.