Shoichiro Yamaguchi

Surface-emitted terahertz-wave difference-frequency generation in periodically poled lithium niobate ridge-type waveguide

We demonstrated surface-emitted terahertz (THz)-wave difference-frequency generation from a periodically poled magnesium-oxide-doped lithium niobate (PPMgLN) ridge-type optical waveguide. The periodic structure in the direction of propagation of the incident laser light was sufficient for surface emission because the incident laser light was confined within a waveguide. Tunable THz waves were generated at around 1 and 1.5 THz using two ridge-type PPMgLN waveguides. The generated THz wavelengths were determined under the quasi-phase matching condition.

Generalized Fresnel Transformations and Their Properties

A theory of generalized Fresnel transformations, which is an important part of transformation of scalar-wave propagating between two quadratic surfaces, is presented. The generalized Fresnel transformation is formulated in terms of generalized Fresnel transform operator T(Z). A set of { T(Z)} has group properties. The differential formulation of the generalized Fresnel transform is obtained by means of functional analytic method. In a special case of the generalized Fresnel transform, one may obtain the differential formula of Fresnel diffraction and Fourier transform.

Epitaxial Growth of MgO-doped Lithium Niobate Thin Films by Metalorganic Chemical Vapor Deposition

Epitaxial MgO-doped lithium niobate [LiNbO3 (LN)] single-crystal thin films with a good surface morphology and crystallinity were grown on lithium tantalate [LiTaO3 (LT)] substrates by low-pressure metalorganic chemical vapor deposition (MOCVD). Dipivaloylmethanatolithium [Li(C11H19O2); Li(DPM)], pentaethoxyniobium [Nb(OC2H5)5; Nb(OEt)5] and bisacetylacetonatomagnesium [Mg(C5H7O2)2; Mg(Acac)2] were used as volatile metalorganic precursors. The crystallinity of the films was investigated by X-ray diffraction measurements. Reciprocal space mapping indicated that good epitaxial growth had been achieved. The film surface was sufficiently smooth to act as a waveguide. The ordinary and extraordinary refractive indices (no and ne) of these as-grown MgO-doped LN thin films were measured to be no=2.2844 and ne=2.1908 at 633 nm, respectively, which were close to those of 3 mol% MgO-doped stoichiometric LN.

Functional Analysis of Diffraction Integral Transform II.

The kernel expansions of a diffraction integral transform, involving the Rayleigh and the Fresnel transforms as special cases, by nonorthogonal mode functions and by complete biorthonormal functions are presented. These biorthonormal functions are the solutions of a differential equation satisfied by Tzf, and the relations between them are obtained. Furthermore in the cylindrical coordinates, an induced orthogonal function system is obtained by the constraint on , and the kernal expansion of the transform by the complete biorthonormal functions is derived by means of the functional analytic method.

Kernel Expansions of Generalized Fresnel Transform

The structural analysis of generalized Fresnel transform space is presented. It is considered that essential properties of generalized Fresnel transform space are included in generalized Fresnel kernel. Systems of orthonormal functions and biorthonormal functions in generalized Fresnel transform space are derived from the generalized Fresnel kernel which is the generating function for those functions. The system of orthonormal functions, which are also called mode functions, is closely related to the modes of propagation in nonorthogonal optical systems. In the special case where the system is orthogonal, these functions can be expressed as the product of two Hermite polynomialss and exponential function. Moreover, it is shown that any generalized Fresnel transform may be expanded in a series by the system of these functions.