This paper proposes an optical power limiter composed of serially connected two tapered velocity couplers consisting partly of nonlinear material. The method of device designing is explained and it is exemplified that the optical output can be regulated stably to a prescribed value over a wide range of optical input. The device performance is simulated by means of FD-BPM algorithm.

Optical logic gates for OR, AND, NOT, and NOR operations in waveguides consisting of nonlinear material are numerically investigated by means of FD-BPM (Finite Difference Beam Propagation Method). The proposed devices are designed utilizing the self-routing characteristics of nonlinear X-crossing structures when they are operated with one input beam or two. The numerical simulations show that the proposed structures can favorably be applied to optical data processing and computing as fundamental logic gates.

A three-dimensional beam propagation method based on a finite element scheme is described for the analysis of second harmonic generation devices. For the wide-angle beam propagation analysis, the Pade approximation is applied to the differential operator along the propagation direction. In order to avoid spurious reflection from the computational windows edges, the transparent boundary condition is introduced. Numerical results are shown for quasi-phase matched second harmonic generation devices using periodically domain-inverted LiNbO3 and LiTaO3 waveguides. The influences of the shape of domain-inverted regions and the inversion width on the conversion efficiencies are investigated in detail.

We examine crossing waveguides with three channels consisting of nonlinear material by means of FD-BPM (Finite Difference Beam Propagation Method). Specifically, we investigate how the insertion of a multimode waveguide into the crossing section of both 13 and 23 structures influences the switching characteristics of output power. We then confirm that these structures can be favorably applied to a wide variety of all-optical devices for integrated optics such as intensity-dependent optical switches, optical power distributors and so on.

We investigate a three-waveguide tapered velocity coupler which consists of a uniform linear, tapered linear and tapered nonlinear slab waveguide. The coupling characteristics depending on the gap width between the waveguides and sloping angle of the tapered waveguides are analyzed by means of the finite difference method. The numerical results show that with realistic structural parameters flat output power characteristics can be obtained over a wide range of input power. It is found that it is possible to use the present structure as a power limiter.

A beam adaptive frame for finite-element beam-propagation analysis is proposed. The width of the frame can be adapted itself to either the guiding structure or the propagating beam in optical circuits, so the size of the computational window can be reduced.