Growth Of KTP Crystals And Study On The Electro-Optical Properties

Potassium titanyl phosphate (KTiOPO4 or KTP) has superior nonlinear-optical and electro-optical (E-O) properties. As a single crystal it has excellent mechanical properties, a good chemically stability and has a high damage threshold. At present, KTP has been widely used in second harmonic generation (SHG), sum (difference)-frequency mixing, optical parametric oscillators (OPO) and optical parametric amplification (OPA). However, KTP also is a strong candidate for the E-O crystal and has promising potential for applications.In this paper, pure and doped KTP crystals were grown from the flux using a top-seeded method, and special technique have been used to lower the electrical conductivity to three orders of magnitude than common flux KTP, the values is up to 10-10(cm)-1, this overcame the shortcoming that common flux KTP cannot be used in E-O application field because of having higher electrical conductivity. The growth condition, doped elements and annealing technology were investigated. Single crystals of KTP with high quality and big Z-cut cross section were obtained by optimizing the parameter of crystal growth.After processing, the cell parameter, transparency, optical damage threshold of KTP crystal have been measured as well as the distribution coefficient of doped elements. The results showed that, after dopping, the cell parameter and transparency of KTP crystal changed little; optical damage threshold increased three orders of magnitude than the common flux KTP, meanwhile, optical homogeneity decresed a little.The tests of E-O applications by our flux KTP has been realized, the results showed: optical waveguides fabricated by using an ion-exchange process, which have an exchange-ion concentration depth profile and refractive-index profile, is close to a complementary error-function distribution, optical homogeneity and device thermal stability is much better. Amplitude modulation switch formed by our flux KTP has the contrast ratio of 150:1 and insert loss is 2.5% at 1064 nm.High quality optical pulse with 1 ns width was cut successfully by using an E-O modulator from a laser pulse with 50 ns width, this modulator had run for three years, and the crystal didn't blackened, it showed our low conductivity flux KTP can endure high modulation voltage for a very long time. Q-switching test of E-O modulator was carried out, the results displayed regular rectangular optical pulse figuration without any acoustic ringing, the leading and trailing edges is 5 ns.Bulk high-speed traveling wave E-O modulator was also fabricated, the half-wave voltage is just 760 V, response time of the device is low up to 297 ps.The results of E-O tests showed that KTP crystals by our flux technique is an attractive material for various E-O applications, especially used in a high-repetition-rate and high responsible laser system.