Masahiro Sasaura

Wide-angle, low-voltage electro-optic beam deflection based on space-charge-controlled mode of electrical conduction in KTa1−xNbxO3

An electro-optic beam deflector with unprecedented performance is demonstrated. A full deflection angle of 250mrad (=14.3°) has been achieved by applying only ±250V to a 0.5-mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0mm. The operating principle is investigated and the origin of the deflection phenomenon is attributed to a nonuniform electric field induced by space-charge-controlled electrical conduction in the crystal.

Space-charge-controlled electro-optic effect: Optical beam deflection by electro-optic effect and space-charge-controlled electrical conduction

This paper describes the experimental and theoretical studies of an anomalous optical beam deflection phenomenon based on electrooptic effect and space-charge-controlled electrical conduction. In the experiment, a large deflection angle of 250mrad (=14.3°) has been observed by applying ±250V to a 0.5‐mm-thick KTa1−xNbxO3 crystal with a short interaction length of 5.0mm. The crystal has a rectangular shape with uniform electrodes and there is no prism shape involved which is a common geometrical shape of crystal, electrode, or ferroelectric domain in the conventional electro-optic deflectors. The operating principle is investigated and it is found that the space-charge-controlled electrical conduction in the crystal plays an essential role in this deflection phenomenon. The electrical conduction is carried by electrons injected from the Ohmic contact of the electrode with the crystal. The injected electrons induce the space-charge effect and the electric field becomes nonuniform between the electrodes. The...

Thermal expansion coefficients of high-Tc superconductor substrate NdGaO3 single crystal

We report the temperature dependence of lattice constants for a NdGaO3 single crystal grown by the Czochralski method and thermal expansion coefficients which were obtained for the first time. Lattice mismatch between the NdGaO3 substrate and YBa2Cu3Ox superconducting film is 0.27% at elevated temperatures and the appropriate expansivities are similar. The crystalline quality of deposited YBa2Cu3Ox films on NdGaO3 by the laser ablation method was extremely good. NdGaO3 is, therefore, an excellent candidate for epitaxial high‐Tc superconducting films.

New Beam Scanning Model for High-Speed Operation Using KTa1-xNbxO3 Crystals

We propose a new beam scanning model that is applicable to electrooptic materials with electron traps. With this model, we can achieve both high-speed operation and wide-angle scanning, because the operating speed is limited not by the electron mobility but by the frequency limit of the electrooptic effect of the materials. The voltage dependence of the scanning angle at 100 kHz using a KTa1-xNbxO3 crystal is consistent with the property predicted by the proposed model.

Preparation of YBa2Cu3O7-y High Tc Thin Films on NdGaO3 Substrate by Laser Ablation

As-grown thin films of YBa2Cu3O7-y with a smooth surface were obtained on lattice-matched NdGaO3 substrates by ArF laser ablation deposition. The as-grown thin film has a zero-resistance temperature (Tc) at 90 K. The full width at half-maximum (FWHM) of the X-ray diffraction peak (005) of the thin film was as narrow as 0.12 degrees. These results suggest that the as-grown YBa2Cu3O7-y films on NdGaO3 substrates were high-quality single crystals. NdGaO3 substrates are thought to be a promising substrate for epitaxial growth of YBa2Cu3O7-y high Tc thin films.

New substrate PrGaO3 for a high Tc superconducting YBa2Cu3Ox epitaxial film

The potential of a new substrate, PrGaO{sub 3}, for high {ital T}{sub {ital c}} oxide superconducting films is investigated and results indicate it is the most suitable material studied so far. Single crystals were grown by the Czochralski method. The lattice mismatch between PrGaO{sub 3} and YBa{sub 2}Cu{sub 3}O{sub {ital x}} superconductor was estimated to be only 0.02% at the elevated deposition temperature. The dielectric constant value was 24 at 10 kHz. The {ital c}-axis oriented YBa{sub 2}Cu{sub 3}O{sub {ital x}} films were deposited onto PrGaO{sub 3} substrates by the laser ablation technique. Their superconducting transition temperature was as high as 90 K, even for a film thickness of only 500 A.

Low-driving-voltage electro-optic modulator with novel KTa1-xNbxO3 crystal waveguides

We have successfully demonstrated a low-driving-voltage electro-optic (EO) modulator using newly developed KTa1-xNbxO3 (KTN) buried waveguides. We prepared high-quality and large KTN crystals. The crystals exhibited a large quadratic EO coefficient of 4.8×10-15 m2/V2 at 1.55 µm. The KTN crystals also exhibited a very large linear EO effect, for example 600 pm/V at a biased potential of 60 V/mm, which is twenty times larger than the r33 of LiNbO3. The waveguide layers for the core and cladding were formed by liquid phase epitaxy techniques on the KTN crystals. The propagation loss was less than 0.5 dB/cm and the polarization dependent loss was less than 0.1 dB/cm. The EO modulators had a low Vπ of <2.5 V (4.0-V biased potential, l=6 mm) and a fast response of 3 GHz.

New substrate PrGaO sub 3 for a high T sub c superconducting YBa sub 2 Cu sub 3 O sub x epitaxial film

The potential of a new substrate, PrGaO{sub 3}, for high {ital T}{sub {ital c}} oxide superconducting films is investigated and results indicate it is the most suitable material studied so far. Single crystals were grown by the Czochralski method. The lattice mismatch between PrGaO{sub 3} and YBa{sub 2}Cu{sub 3}O{sub {ital x}} superconductor was estimated to be only 0.02% at the elevated deposition temperature. The dielectric constant value was 24 at 10 kHz. The {ital c}-axis oriented YBa{sub 2}Cu{sub 3}O{sub {ital x}} films were deposited onto PrGaO{sub 3} substrates by the laser ablation technique. Their superconducting transition temperature was as high as 90 K, even for a film thickness of only 500 A.

Fast Response Variable Focal-Length Lenses Using KTa1-xNbxO3 Crystals

We fabricated variable focal length lenses with fast responses by using the strong Kerr effect of KTa1-xNbxO3 single crystals. We observed focus shifts of about 40 mm with the assistance of a 250-mm-focal-length lens, which corresponds to a focus shift from infinity to 1.56 m without the assisting lens. The time response was as fast as 1 µs.

Fast response varifocal lenses using KTa 1−x Nb x O 3 crystals and a simulation method with electrostrictive calculations

We fabricated cylindrical varifocal lenses with fast responses by using the strong Kerr effect of KTa(1-x)Nb(x)O(3) (KTN) single crystals. We observed focus shifts of up to 87 mm with the assistance of a 250 mm focal length lens, which corresponds to a focus shift from infinity to 720 mm by the KTN lens itself. The response time was as fast as 1 μs. We also present a simulation method for calculating refractive index distributions in KTN single crystals, which is essential when designing the lens. The method is characterized by the strain contribution, which has not conventionally been typical of electro-optic simulations. We used this method to explain the refractive index modulations that are characteristic of the varifocal lenses.