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The proton-exchanged waveguide formed on MgO-doped lithium niobate crystals is resistant to the optical damage or the photorefractive effect. Therefore, this waveguide is believed to be a promising device for optical information and processing. However, the optical damage can also be an important problem for this waveguide in the communication wavelength since the high-power optical source is used. In this report, a brief general review on the optical properties and its practical application of the lithium niobate crystal as the optical waveguide are given. Then the experimental research work aimed to clarify the properties and its mechanism of the electrooptic effect and the optical damage or photorefractivity of the lithium niobate optical waveguide is described. In this work, the optical damage in this proton-exchanged waveguide is measured quantitatively at various optical wavelengths including blue and red light by using the holographic grating method and the infrared communication wavelength (1550nm) by using the prism coupler method. The optical damage is significant not only in blue wavelength but also in the red, and even at 1550 nm with high power (100 mW) laser diode for communication. So the optical damage cannot be negligible also in the communication wavelengths. The effect of annealing temperature is also discussed. At the relatively high temperatures, the optical damages are founde to be annealed out. The effect of the applied electric field to the optical damage is experimentally discussed and its enhancement is observed to the applied d.c. and a.c. fields. In conclusion, the optical properties as the electrooptic constant and the optical damage are experimentally measured and the many fundamental data are obtained to realize the useful and practical optical devices.

By near-infrared spectroscopy, we classified water molecules in hydrated gelatin membranes in a drying process. Absorbance spectra in the frequency range of 4500–5500 cm−1 were resolved into three peaks, S0, S1, and S2, that correspond to water molecules with different hydrogen bond states. From the areas of the absorbance peaks as a function of the water content of gelatin, together with the information on the freezing properties of water measured by differential scanning calorimetry, we found that, when the water content is less than 20%, free water disappears and only weakly and strongly bound waters remain. We also found that the weakly bound water consists of S0, S1, and S2 water molecules with a simple composition of . Using this information, most of the freezable water was determined to be free water. Our classification provides a simple method of estimating the retention and freezing properties of processed foods or drugs by infrared spectroscopy.

There is a great demand for the electrooptic devices for optical communication and also for optical sensor applications. The properties of these devices are highly dependent on the waveguide fabrication process. The exact estimation of the optical and physical properties of the waveguides becomes necessary. The purpose of this study is quantitative estimation of the photorefractive effect of the lithium niobate waveguides.

The temperature and electric field dependences of the photorefractive effect in proton-exchanged (PE) waveguides formed on MgO-doped lithium niobate (LN) are investigated in detail for the first time. As a result, the photorefractive effect (optical damage) is found to be enhanced by the electric field applied to the waveguide. On the other hand, resistance to the photorefractive effect is markedly increased when the samples are heated at temperatures as high as 80°C. We should take these properties into consideration in designing optical devices such as electrooptic modulators and parametric devices.

The Kerr constants in C 6 H 6 and C 6 H 5 NO 2 are discussed by means of the statistical mechanics of Maxwell-Boltzmann's distribution of the molecules under the biasing field. The anisotropic electronic polarizabilities are obtained as α 1 =12.06(A 3 ) (parallel to C 6 H 6 plane) and α 2 =7.143 (A 3 ) (perpendicular to C 6 H 6 plane) for the Kerr constant 6.0×10 -18 in C 6 H 6 , and also α 3 =13.644 (A 3 ) (parallel to the polar axis) and α 1 +α 2 =26.50 (A 3 ) for the Kerr constant 269×10 -7 in C 6 H 5 NO 2 .