We present a temperature-dependent Sellmeier equation for the refractive index of stoichiometric LiTaO3. The extraordinary refractive index, for the range 0.39-4.1 microm and for temperatures of 30-200 degrees C, are based on previously published data [Jpn. J. Appl. Phys. 41, 465 (2002)] and on measured data derived from quasi-phase-matched (QPM) resonances. We used the new Sellmeier coefficients that we obtained to calculate the QPM wavelengths for an optical parametric oscillator (OPO) based on periodically poled stoichiometric LiTaO3 pumped at 1064 nm. The measured wavelengths of the OPO were in good agreement with our predictions.

Studies of dielectric spectroscopy, dc conductivity, and polarization switching allowed the observation of phase transition from the superionic to the insulating state in flux-grown KTiOPO4 (KTP) crystals at low temperature where the high mobility of potassium ions is suppressed. A low temperature method of fabrication of engineered periodic domain structures in superionic KTP and isomorphic crystals is proposed. It enabled us to tailor homogeneous domain gratings with various periods in the range 4–39 μm for quasiphase-matched nonlinear optical converters in KTP plates over whole area of 30×30 mm2.

We report the nondestructive investigation and visualization of periodically poled domains in ferroelectric potassium titanyl phosphate (KTP) crystals using polarization sensitive scanning force microscopy (SFM). Applying an alternating voltage technique to SFM allows ferroelectric domain wall resolution beyond 100 nm. Image contrast between KTP and Rb doped KTP, i.e., rubidium titanyl phosphate (RTP) regions arises from the differential piezoelectric response. We find the polarization vectors in both KTP and RTP to be aligned parallel to the negative z axes as deduced (a) when comparing our data with a ferroelectric reference sample, i.e., tri-glycine sulfate (b) from comparison of nanoscale hysteresis loops recorded on KTP and RTP, and (c) from direct domain switching in KTP applying very high electric fields between tip and counter electrode. The latter experiments show that nanoscale ferroelectric domains in KTP switch from the negative to the positive z-axes alignment for electric fields stronger than 750 V/cm. Nevertheless, spontaneous backswitching is observed after a couple of minutes.

Dominant factors influencing domain broadening in periodically poled ferroelectric domain structures for quasi-phase-matched nonlinear optical converters are studied. It is shown that fabricated patterned switching electrode gives rise to a high tangential field causing polarization inversion behind an isolated layer of the patterned electrode. The domain broadening depends on basic electron parameters of a ferroelectric crystal such as surface electron concentration and electron mobility.

A new mechanism for polarization rotation in rib waveguides is suggested and demonstrated in InP waveguides. The polarization rotation is achieved by loading a rib waveguide in a periodic asymmetric way. Complete TE↔TM conversion, with only 2–3 dB excess loss, is obtained in a 3.7-mm-long InP loaded waveguide. Strong polarization rotation (80%), in shorter devices (0.3 mm long), is also demonstrated.