M. Koshiba

Enhancement of the guided‐wave second‐harmonic generation in the form of Cerenkov radiation

A method for enhancing guided‐wave second‐harmonic generation (SHG) phase matched by a Cerenkov radiation scheme by means of tailoring the transverse (y direction) nonlinear susceptibility profile in the waveguide channel is proposed. Specifically, linear and domain‐inverted (poled) channels embedded in a nonlinear substrate are considered, and the SHG efficiency for each structure is compared with that for the conventional nonlinear channel without domain inversion. Through electromagnetic field analysis, a significant enhancement of SHG is demonstrated, particularly with the domain inverted channel.

Stress analysis method for elastically anisotropic material based optical waveguides and its application to strain-induced optical waveguides

A numerical approach for the stress analysis of elastically anisotropic material-based optical waveguides is newly formulated with the finite element method (FEM). The stress analysis method developed here is linked to the guided mode analysis method to produce a two-step analysis of acoustooptic modulation of optical waveguides. Numerical examples are shown for strain-induced optical waveguides on LiNbO/sub 3/ substrates.

Vectorial wave analysis of side-tunnel type polarization-maintaining optical fibers by variational finite elements

Vectorial wave analysis of side-tunnel type polarization-maintaining optical fibers is presented using the vector H -field finite-element method, which is applicable to the fibers having arbitrarily cross-sectional shape. First, to improve the accuracy of solutions, several techniques are investigated such as the zero-extrapolation method, curvilinear elements, and an improved virtual-boundary method. After checking the accuracy of solutions, the relation between the shape of the fibers and their polarization-mode properties, such as the axial propagation constants, the modal birefringence, the polarization-mode dispersion, and the magnetic-field distribution, is studied in detail. Also studied are the optical fields of side-tunnel fibers, which have never been investigated, and the mechanism for the phenomenon that the propagation constants of the fundamental modes come extraordinarily close to those of the first higher-order modes is clarified.

Dispersion compensation based on dual-mode optical fiber with inhomogeneous profile core

It is well known that the first higher order mode of optical fibers exhibits large negative waveguide dispersion by operating close to its cutoff wavelength. By using this dispersion, the positive dispersion in conventional 1.3 /spl mu/m zero dispersion optical fibers for 1.55 /spl mu/m signal light can be compensated. In this paper, we focus on the dispersion compensation technique using the first higher order mode in a dual-mode optical fiber, which supports both the fundamental LP/sub 01/ and first higher order LP/sub 11/ modes. Numerical calculations show that the waveguide dispersion of the first higher order mode is very sensitive to the refractive-index profile of optical fibers. In addition, it is demonstrated that a directional coupler composed of a single-mode fiber and a dual-mode fiber operates as a mode converter, which converts the signal light from the LP/sub 01/ mode to the LP/sub 11/ mode.

Finite element beam propagation method with perfectly matched layer boundary conditions for three-dimensional optical waveguides

The perfectly matched layer boundary condition is incorporated into the beam propagation method based on a finite element scheme for 3-D optical waveguides. Not only an approximate scalar formulation but a full-wave formulation is presented. Its effectiveness is verified by way of numerical examples. Copyright

Vectorial wave analysis of stress-applied polarization-maintaining optical fibers by the finite-element method

A vectorial wave analysis of stress-applied polarization-maintaining optical fibers is presented using a vector H -field finite-element method. In this approach, the divergence-free constraint for H is imposed and the spurious, nonphysical solutions which are included in the solutions of earlier vectorial finite-element methods do not appear in a guided region. In order to verify the accuracy of solutions, numerical results for a step-index circular-core fiber are presented and compared with exact ones. We also propose an approximate method for calculating the splice loss between two optical fibers and show the normalized radiated power caused by transverse offset between two stress-applied optical fibers.

Group‐velocity‐matched second‐harmonic generation: An efficient scheme for femtosecond ultraviolet pulse generation in periodically domain‐inverted β‐BaB2O4

With the combined use of the group‐velocity‐matched and the quasi‐phase‐matched frequency doubling in β‐BaB2O4, femtosecond ultraviolet pulse generation is found to be realizable with high efficiency. Calculation of the group‐velocity mismatch shows that at ∼630 nm wavelength of the pump pulse the mismatch vanishes completely. Typical design parameters such as the walk‐off length, the dispersion lengths, and the quasi‐phase‐matching period are evaluated numerically around the zero walk‐off wavelength. Temperature tuning of the operation wavelength is investigated as well.

Algebraically decaying modes of dielectric planar waveguides

We show analytically that, at a critical point where the effective refractive index of a mode coincides with the bulk index of a substrate region, for certain graded-index planar waveguides there exists a family of bound modes with algebraic (power-law) tails in the evanescent field.

Modeling and design optimization of hole-assisted lightguide fiber by full-vector finite element method

The full-vector finite element method with perfectly matched layer has realized accurate modeling of chromatic dispersion and bending loss of the hole-assisted lightguide fiber for the first time. Optimal design for large anomalous dispersion fiber is also presented.

Multidimensional solitons in cubic nonlinear media.

We show numerically that, contrary to what has been believed so far, multidimensional optical solitons can propagate in cubic nonlinear media. To avoid a collapse along the propagation axis, we take advantage of the cross-phase modulations between fundamental- and harmonic-field components. A compact analytical expression for new solitonlike fields with an arbitrary transverse dimension is derived through a self-consistent-field approximation.